Complications of the percutaneous kidney biopsy

Automatic renal carcinoma biopsy guidance using forward-viewing endoscopic optical coherence tomography and deep learning

Percutaneous renal biopsy is commonly used for kidney cancer diagnosis. However, the biopsy procedure remains challenging in sampling accuracy. Here we introduce a forward-viewing optical coherence tomography probe for differentiating tumor and normal tissues, aiming at precise biopsy guidance. Totally, ten human kidney samples, nine of which had malignant renal carcinoma and one had benign oncocytoma, were used for system evaluation. Based on their distinct imaging features, carcinoma could be efficiently distinguished from normal renal tissues. Additionally, oncocytoma could be differentiated from carcinoma. We developed convolutional neural networks for tissue recognition. Compared to the conventional attenuation coefficient method, convolutional neural network models provided more accurate carcinoma predictions. These models reached a tissue recognition accuracy of 99.1% on a hold-out set of four kidney samples. Furthermore, they could efficiently distinguish oncocytoma from carcinoma. In conclusion, our convolutional neural network-aided endoscopic imaging platform could enhance carcinoma diagnosis during percutaneous renal biopsy procedures.

Feasibility and Safety of Percutaneous Kidney Biopsy in Small Kidneys: Breaking the Paradigm

INTRODUCTION

The percutaneous kidney biopsy (PKB) is an essential tool in nephrology; small kidney size has been a relative contraindication to PKB and there is limited data on the safety and utility of performing PKB in this setting. Our aim was to describe the complications of PKB in small kidneys and to assess if kidney biopsy results have an impact on medical decisions and outcomes.

METHODS

This was a retrospective, descriptive, and observational study. Patients older than 16 years of age with a decreased kidney size (≤8 cm) and undergoing PKB of native kidneys from July 2019 to December 2022 were included.

RESULTS

Twenty-five patients were included, 19 women and 6 men. The mean age was 42.3 ± 18.04. The mean kidney length was 7.56 ± 0.33 and the mean width was 4.2 cm. All patients received only 1 puncture, obtaining an average of 12 glomeruli. The mean blood urea nitrogen and serum creatinine were 36 mg/dL and 1.94 mg/dL, respectively and the mean Hgb (hemoglobin) was 12.87 ± 2.81 g/dL. Minor complications occurred in 5 patients, perirenal hematoma in 3 patients, hematuria in 1 patient, and hematoma plus hematuria in 1 patient. Histological examination showed FSGS, lupus nephritis, other Glomerular disease, crescentic glomerulonephritis, and tubulointerstitial nephritis in 36%, 20%, 16%, 16%, and 12% of the cases, respectively. Biopsy resulted in management modification in 64% of cases. In a bivariate analysis, kidney size was not associated with higher complication rates.

CONCLUSIONS

PKB in small kidneys is a feasible and safe procedure when properly planned, providing an adequate sample in all cases, with an insignificant number of minor complications, and that is clinically relevant.

Percutaneous kidney biopsies in children: a 24-year review in a tertiary center in northern Portugal

INTRODUCTION

Percutaneous kidney biopsy (KB) is crucial to the diagnosis and management of several renal pathologies. National data on native KB in pediatric patients are scarce. We aimed to review the demographic and clinical characteristics and histopathological patterns in children who underwent native percutaneous KB over 24 years.

METHODS

Retrospective observational study of patients undergoing native percutaneous KB in a pediatric nephrology unit between 1998 and 2021, comparing 3 periods: period 1 (1998-2005), period 2 (2006-2013), and period 3 (2014-2021).

RESULTS

We found that 228 KB were performed, 78 (34.2%) in period 1, 91 (39.9%) in period 2, and 59 (25.9%) in period 3. The median age at KB was 11 (7-14) years. The main indications for KB were nephrotic syndrome (NS) (42.9%), hematuria and/or non-nephrotic proteinuria (35.5%), and acute kidney injury (13.2%). Primary glomerulopathies were more frequent (67.1%), particularly minimal change disease (MCD) (25.4%), IgA nephropathy (12.7%), and mesangioproliferative glomerulonephritis (GN) (8.8%). Of the secondary glomerulopathies, lupus nephritis (LN) was the most prevalent (11.8%). In group 1, hematuria and/or non-nephrotic proteinuria were the main reasons for KB, as opposed to NS in groups 2 and 3 (p < 0.01). LN showed an increasing trend (period 1-3: 2.6%-5.3%) and focal segmental glomerular sclerosis (FSGS) showed a slight decreasing trend (period 1-3: 3.1%-1.8%), without statistical significance.

CONCLUSIONS

The main indication for KB was NS, which increased over time, justifying the finding of MCD as main histological diagnosis. LN showed an increase in incidence over time, while FSGS cases did not increase.

Metabolomics study reveals blood biomarkers for early diagnosis of chronic kidney disease and IgA nephropathy: A retrospective cross-sectional study

BACKGROUND AND AIMS

Chronic kidney disease (CKD) causes low quality of life and alarming morbidity and mortality. The crucial to retard CKD progression is to diagnose early for timely treatment. IgA nephropathy (IgAN) is a typical CKD and the most common glomerulonephritis. Both CKD and IgAN lack accurate and sensitive blood biomarkers for early diagnosis. Here we report the potential of plasma biomarkers for early diagnosis of CKD and IgAN.

MATERIALS AND METHODS

Plasma levels of metabolites derived from tryptophan were quantified with an LC-MS/MS-based metabolomics for two cohorts. Based on the predictive probability of each metabolite, multivariate models including logistic regression and random forest were used to establish the early diagnostic biomarkers for CKD and IgAN.

RESULTS

The plasma melatonin diagnosed early CKD (stages Ⅰ-Ⅱ) with an accuracy exceeding 95%, and a panel of melatonin and tryptophan achieved a remarkable 100% accuracy in diagnosing early CKD. Furthermore, indole-3-lactic acid had an excellent ability to distinguish IgAN among CKD patients. Based on the CKD screening and IgAN diagnosis primarily contributed by melatonin and indole-3-lactic acid, early IgAN could be diagnosed with an accuracy of over 85%.

CONCLUSIONS

This study provides promising plasma biomarkers for early diagnosis of CKD and IgAN.

Bleeding complications after percutaneous kidney biopsies - nationwide experience from Brunei Darussalam

BACKGROUND

Kidney biopsy serves as a valuable method for both diagnosing and monitoring kidney conditions. Various studies have identified several risk factors associated with bleeding complications following the procedure, but these findings have shown inconsistency and variation.

AIM

To investigate the risk of bleeding complications following percutaneous kidney biopsy in Brunei Darussalam. We sought to explore the relevant clinical and pathological risk factors associated with these complications while also considering the findings within the broader international literature context.

METHODS

We conducted a retrospective study of all adult patients who underwent kidney biopsy in Brunei Darussalam from October 2013 to September 2020. The outcomes of interest were post-biopsy bleeding and the need for blood transfusions. Demographics, clinical, laboratory and procedural-related data were collected. Logistic regression analysis was used to identify predictors of outcomes.

RESULTS

A total of 255 kidney biopsies were included, with 11% being performed on transplanted kidneys. The majority of biopsies were done under ultrasound guidance (83.1%), with the rest under computer tomography guidance (16.9%). The most common indications for biopsy were chronic kidney disease of undefined cause (36.1%), nephrotic syndrome (24.3%) and acute kidney injury (11%). Rate of bleeding complication was 6.3% - 2% frank hematuria and 4.3% perinephric hematoma. Blood transfusion was required in 2.8% of patients. No patient lost a kidney or died because of the biopsy. Multivariate logistic regression identified baseline hemoglobin [odds ratio (OR): 4.11; 95% confidence interval (95%CI): 1.12-15.1; P = 0.03 for hemoglobin ≤ 11 g/dL vs. > 11 g/dL) and the presence of microscopic hematuria (OR: 5.24; 95%CI: 1.43-19.1; P = 0.01) as independent risk factors for post-biopsy bleeding. Furthermore, low baseline platelet count was identified as the dominant risk factor for requiring post-biopsy transfusions. Specifically, each 10 109/L decrease in baseline platelet count was associated with an 12% increase risk of needing transfusion (OR: 0.88; 95%CI: 0.79-0.98; P = 0.02).

CONCLUSION

Kidney biopsies were generally well-tolerated. The identified risk factors for bleeding and transfusion can help clinicians to better identify patients who may be at increased risk for these outcomes and to provide appropriate monitoring and management.

Automatic renal carcinoma biopsy guidance using forward-viewing endoscopic optical coherence tomography and deep learning

Percutaneous renal biopsy (PRB) is commonly used for kidney cancer diagnosis. However, current PRB remains challenging in sampling accuracy. This study introduces a forward-viewing optical coherence tomography (OCT) probe for differentiating tumor and normal tissues, aiming at precise PRB guidance. Five human kidneys and renal carcinoma samples were used to evaluate the performance of our probe. Based on their distinct OCT imaging features, tumor and normal renal tissues can be accurately distinguished. We examined the attenuation coefficient for tissue classification and achieved 98.19% tumor recognition accuracy, but underperformed for distinguishing normal tissues. We further developed convolutional neural networks (CNN) and evaluated two CNN architectures: ResNet50 and InceptionV3, yielding 99.51% and 99.48% accuracies for tumor recognition, and over 98.90% for normal tissues recognition. In conclusion, combining OCT and CNN significantly enhanced the PRB guidance, offering a promising guidance technology for improved kidney cancer diagnosis.

Discrepancies between clinical and pathological findings seen at renal biopsy in rheumatological diseases

OBJECTIVE

Renal biopsy contributes to the diagnosis, follow-up, and treatment of many rheumatic conditions. This study assessed the diagnostic role and safety of renal biopsies in a tertiary rheumatology clinic.

METHODS

Renal biopsies performed between June 2020 and December 2022 were screened, and demographic, clinical, histopathological, and safety data were collected from patient records.

RESULTS

In this study, 33 males and 38 females were included. Except for 1 patient who received acetylsalicylic acid, antiaggregant, and/or anticoagulant drugs were stopped before the biopsy. Complications included a decrease of hemoglobin in 8 patients (11.3%) and microscopic hematuria in 40 patients (56.3%). Control ultrasonography was performed in 16 patients (22.5%), and a self-limiting hematoma was found in 4 of them (5.6%) without additional complications. While less than 10 glomeruli were obtained in 9 patients (9.9%), diagnosis success was 94.4%. Histopathological data were consistent with one of the pre-biopsy diagnoses in 54 of 67 cases (80.6%) but showed discrepancies in 19.4% (n=13) of patients. A repeat biopsy was performed in 7 patients for re-staging or insufficient biopsy.

CONCLUSIONS

Renal biopsy significantly contributes to rheumatology practice, especially in patients with complex clinical and laboratory findings or in whom different treatments can be given according to the presence, severity, and type of renal involvement. Although the possibility of obtaining insufficient tissue and the need for re-staging and repeat biopsy in the follow-up might be expected, complication risk does not seem to be a big concern. Renal biopsy often evidenced discrepancies between pre-biopsy diagnosis and histopathological findings.

Acute presentation of renal pseudoaneurysms in a patient with systemic lupus erythematosus after percutaneous renal biopsy

The development of renal pseudoaneurysms following percutaneous kidney biopsy is a rare but potentially dangerous complication due to the risk of rupture with subsequent hemorrhage. We describe a female patient in her 20s with long-standing lupus nephritis who presented to the hospital for elective CT-guided left renal biopsy that was complicated by pseudoaneurysms in the bilateral kidneys. Post-biopsy, she developed a perinephric hematoma that extended to the upper pelvis with resultant superior displacement and diminished blood flow to the left kidney. Successful endovascular coil embolization was performed after left renal artery angiography confirmed contrast extravasation in one of the branches that supplied the inferior pole of the left kidney. Despite the embolization, her hemoglobin continued to decline, and a subsequent CT-scan demonstrated a persistent loculated hyperdense fluid collection in the beforementioned area. Repeat angiography revealed multiple left renal pseudoaneurysms and a single pseudoaneurysm in the upper pole of the right kidney, neither of which were previously visualized. The acute development of pseudoaneurysms due to accidental or non-accidental trauma is a well-established entity. Here we present a patient that acutely developed numerous arterial pseudoaneurysms after renal biopsy and has never been reported in the literature. Special caution should be undertaken in the case of high-risk patients predisposed to these pseudoaneurysms.

Model-Based Needle Identification Using Image Analysis and Needle Library Matching for Ultrasound-Guided Kidney Biopsy: A Feasibility Study

OBJECTIVE

The aim of the work described here was to determine the feasibility of using a novel biopsy needle detection technique that achieves high sensitivity and specificity in a trade-off of resolution, detectability and depth of imaging.

METHODS

The proposed needle detection method consists of a model-based image analysis, temporal needle projection and needle library matching: (i) Image analysis was formulated under the signal decomposition framework; (ii) temporal projection converted the time-resolved needle dynamics into a single image of the desired needle; and (iii) the enhanced needle structure was spatially refined by matching a long, straight linear object in the needle library. The efficacy was examined with respect to different needle visibility.

RESULTS

Our method effectively eliminated confounding effects of the background tissue artifacts more robustly than conventional methods, thus improving needle visibility even with the low contrast between the needle and tissue. The improvement in needle structure further resulted in an improvement in estimation performance for the trajectory angle and tip position.

CONCLUSION

Our three-step needle detection method can reliably detect needle position without the need for external devices, increasing the needle conspicuity and reducing motion sensitivity.

Risk of bleeding-related complications after kidney biopsy in patients with systemic lupus erythematosus

OBJECTIVE

Kidney biopsy is essential for the diagnosis and classification of lupus nephritis. Percutaneous biopsy has a risk of bleeding-related complications; however, data on the risk of percutaneous kidney biopsy in patients with systemic lupus erythematosus (SLE) are scarce. In this study, we aimed to investigate the rate of bleeding-related complications and to examine the risk factors for complications of kidney biopsy in patients with systemic lupus erythematosus (SLE).  METHODS: We retrospectively reviewed the medical records of patients with SLE who underwent ultrasound-guided percutaneous kidney biopsy between 2002 and 2020 at a tertiary referral center. Minor complications were defined as hematoma and passing hematuria not requiring an intervention. Major complications included bleeding events that required interventions after the biopsy. Statistical analysis with a multivariate logistic regression model was performed.

RESULTS

In a total of 277 patients with SLE, the rate of overall bleeding-related complications after kidney biopsy was 19.9% (minor 13.0%; major 6.9%). Among patients with major complications, 84.2% needed blood transfusion alone without embolization or surgery, whereas the remaining three patients needed embolization for bleeding control. Multivariate analysis revealed that thrombocytopenia (odds ratio [OR] 7.186, 95% confidence interval [CI] 2.315-22.300), and low eGFR (OR 3.478, 95% CI 1.094-11.056) were significantly associated with the risk of major bleeding-related complications after kidney biopsy.

CONCLUSION

Percutaneous kidney biopsy is accompanied by the risk of bleeding-related complications; however, most events in our study did not require vascular intervention for bleeding control. Low platelet count and low estimated glomerular filtration rate (eGFR) significantly increase the risk of complications after kidney biopsy in patients with SLE. Key Points • The rate of overall bleeding-related complications after kidney biopsy was about 20% of patients with SLE. • The most commonly observed events were gross hematuria followed by blood transfusion. • Thrombocytopenia and poor kidney function areis an important risk of bleeding-related complications after kidney biopsy.

What happens after the kidney biopsy? The findings nephrologists should know

Background

Percutaneous kidney biopsies are important tools for the diagnosis of kidney diseases. Nephrologists must be familiar with the expected complications of the procedure to provide an adequate informed consent. Here, we present a quality improvement analysis that reviews the complication rate of percutaneous kidney biopsies performed over a 2-year period by nephrologists at a single center, and that tabulates the nature and timing of these events.

Methods

From a single center cohort, pre- and post-biopsy anthropomorphic and clinical measurements were collected. Post-biopsy complications were tracked and sorted into either major or minor complications. Statistical tests were used to analyze complication incidence across the pre- and post-biopsy measurements obtained.

Results

Of the 154 nephrologist-performed percutaneous native kidney biopsies, 2 biopsies (1.3%) were found to result in a major complication. Both major complications were detected within 4 hours of the biopsy. Analysis of the pre-biopsy and post-biopsy measurements found that the proportion of complications was higher in patients with hematuria prior to biopsy. It was also found that patients with complications were statistically younger and had fewer comorbidities. Under univariable analysis, older age was associated with a lower incidence rate ratio for complications. However, no pre-or-post biopsy measurement or characteristic had a statistically significant change in incidence rate ratio under multivariable analysis.

Conclusions

Percutaneous kidney biopsies were found to be low risk when performed by nephrologists in this single center cohort. Consistent with past literature, life threatening major complications rarely occurred and were reliably identified within 4 hours of biopsy, suggesting that centers can consider reduced observation times without compromising patient safety. Minor complications, such as pain, were more likely to occur in younger, healthier patients, and in those with hematuria prior to biopsy. This extensive tabulation of all biopsy adverse events is the first of its kind and will be beneficial for nephrologists to inform discussions with patients about expectations and risk-benefit of this procedure.

Efficacy and safety of percutaneous renal biopsy performed using 18G needle versus 16G needle: a single-center retrospective study

Background

At present, both 16G and 18G needles are used for percutaneous renal biopsy in China. This study aimed to compare the efficacy and safety of biopsy performed with the 18G needle vs. the 16G needle.

Methods

The data of patients who underwent percutaneous renal biopsy at our hospital between January 2015 and December 2019 were retrospectively analyzed. The number of glomeruli obtained by puncture and postoperative complications were compared between patients undergoing biopsy with the 16G and 18G needles. Continuous variables were compared by the t test or the Mann–Whitney U test, and categorical variables by the chi-square test. Correlation analysis was used to examine the relationship of different variables with hematoma size.

Results

Of the total 3138 kidney biopsies, 2526 were performed with the18G needle and 612 with the 16G needle. The number of glomeruli obtained was not significantly different between the two groups (P = 0.078). Large hematomas were significantly more common the 16G group than in the 18G group (9.31% vs. 5.98%, P = 0.003). Arteriovenous fistula was also more common in the 16G group (1.14% vs. 0.23%, P = 0.005). Other complications were rare, with similar incidence in the two groups.

Conclusion

The 18G needle is as effective as the 16G needle for percutaneous renal biopsy. The risk of large hematoma and arteriovenous fistula appear to be lower with the 18G needle.

Kidney Ultrasound for the Nephrologist: A Review

Ultrasound imaging is a key investigatory step in the evaluation of chronic kidney disease and kidney transplantation. It uses nonionizing radiation, is noninvasive, and generates real-time images, making it the ideal initial radiographic test for patients with abnormal kidney function. Ultrasound enables the assessment of both structural (form and size) and functional (perfusion and patency) aspects of kidneys, both of which are especially important as the disease progresses. Ultrasound and its derivatives have been studied for their diagnostic and prognostic significance in chronic kidney disease and kidney transplantation. Ultrasound is rapidly growing more widely accessible and is now available even in handheld formats that allow for bedside ultrasound examinations. Given the trend toward ubiquity, the current use of kidney ultrasound demands a full understanding of its breadth as it and its variants become available. We described the current applications and future directions of ultrasound imaging and its variants in the context of chronic kidney disease and transplantation in this review.

Safety of Obtaining an Extra Biobank Kidney Biopsy Core

Background and objectives: Kidney biopsy (KB) is the “gold standard” for the diagnosis of nephropathies and it is a diagnostic tool that presents a low rate of complications. Nowadays, biobank collections of renal tissue of patients with proven renal pathology are essential for research in nephrology. To provide enough tissue for the biobank collection, it is usually needed to obtain an extra kidney core at the time of kidney biopsy. The objective of our study is to evaluate the complications after KB and to analyze whether obtaining an extra core increases the risk of complications. Material and methods: Prospective observational study of KBs performed at Vall d’Hebron Hospital between 2019 and 2020. All patients who accepted to participate to our research biobank of native kidney biopsies were included to the study. Clinical and laboratory data were reviewed and we studied risk factors associated with complications. Results: A total of 221 patients were included, mean age 56.6 (±16.8) years, 130 (58.8%) were men, creatinine was 2.24 (±1.94) mg/dL, proteinuria 1.56 (0.506–3.590) g/24 h, hemoglobin 12.03 (±2.3) g/dL, INR 0.99 (±0.1), and prothrombin time (PT) 11.86 (±1.2) s. A total of 38 patients (17.2%) presented complications associated with the procedure: 13.1% were minor complications, 11.3% (n = 25) required blood transfusion, 1.4% (n = 3) had severe hematomas, 2.3% (n = 5) required embolization, and 0.5% (n = 1) presented arterio-venous fistula. An increased risk for complication was independently associated with obtaining a single kidney core (vs. 2 and 3 cores) (p = 0.021). Conclusions: KB is an invasive and safe procedure with a low percentage of complications. Obtaining an extra kidney core for research does not increase the risk of complications during the intervention, which remains low in concordance with previously published reports.

The optimal anti-phospholipase A2 receptor cutoff for the diagnosis of idiopathic membranous nephropathy: a single-center retrospective study

BACKGROUND/AIMS

Anti-phospholipase A2 receptor (PLA2R) autoantibody is the main biomarker of idiopathic membranous nephropathy (IMN). We aimed to find a new cutoff value of anti-PLA2R for patients with IMN and to explore the relevance between this antibody and baseline clinical parameters.

METHODS

A total of 670 subjects including 374 IMN cases and 296 non-IMN controls were included between January 2017 and January 2020. All clinical parameters were collected at the time of renal biopsy. The levels of anti-PLA2R were detected by a commercial enzyme-linked immunosorbent assay (ELISA) kit. The optimal cutoff value was calculated by a receiver operating characteristic curve and compared in diagnostic efficiency.

RESULTS

The optimal cutoff value of anti-PLA2R for IMN was 7.45 RU/mL with the highest Youden index, and the corresponding sensitivity, specificity, positive predictive value and negative predictive value were 80.75%, 97.97%, 98.05% and 80.11%, respectively. Anti-PLA2R levels in IMN patients demonstrated a significant positive correlation with serum creatinine and 24-hour urinary protein, while they showed a negative correlation with serum albumin and estimated glomerular filtration rate.

CONCLUSION

The recommended cutoff value of anti-PLA2R is 7.45 RU/mL using ELISA detection for distinguishing IMN from non-IMN nephropathy. The level of anti-PLA2R is related to baseline renal function in IMN. This new threshold can improve the diagnostic efficiency and facilitate early diagnosis of IMN.

Risk factors for biopsy complications in initial versus subsequent biopsies in native and transplant kidneys

BACKGROUND

Few studies exist about risk factors for complications in subsequent biopsies.

PURPOSE

To explore risk factors for complications in initial versus subsequent biopsies in native and transplant kidneys, which may predict biopsy complications.

MATERIAL AND METHODS

In a multicenter study, 2830 native kidney biopsies (4.3% subsequent) were analyzed for major complications (1251 of these were also analyzed for minor) and 667 transplant kidney biopsies (29% subsequent) were analyzed for major and minor complications. No death or nephrectomy were described. Fisher's exact test, Student's t-test, chi-square analyses, and univariate and multiple binary logistic regression analyses were employed; P < 0.05 was considered significant.

RESULTS

In initial native kidney biopsies, the frequency of major complications was higher in women compared to men (odds ratio 1.6, 95% confidence interval 1.1-2.2), in younger patients (50 vs. 54 years, P = 0.007), and in patients with lower weight (78 vs. 82 kg, P = 0.005). In subsequent native kidney biopsies, patients with major complications had a higher systolic blood pressure (145 vs. 132 mmHg, P = 0.03). In initial transplant kidney biopsies, biopsies with major complications had less glomeruli in the biopsy (17 vs. 24, P = 0.046). In subsequent transplant kidney biopsies, patients with major complications had a higher mean arterial pressure (112 vs. 98 mmHg, P = 0.002). In subsequent native kidney biopsies, there was a higher number of SLE-nephritis (12% vs. 4.6%, P = 0.001) compared to initial biopsies.

CONCLUSION

The different types of risk factors for complications in initial versus subsequent renal biopsies could be important for the clinicians to improve patients' safety.

Learning curve for the laparoscopy-guided kidney biopsy procedure in small corpses of dogs and pigs

The use of renal biopsy through laparoscopy is increasingly present both in human and veterinary medicine. However, both techniques require skill and training to make the operator capable to do it. The learning curve allows the quantitative and qualitative assessment of the number of attempts and minimum time for the surgical procedure. The objective included establish the learning curve for laparoscopy-guided kidney biopsy procedures in dog and pig corpses. Six dogs and six pigs corpses weighing less than 10 kg were used for this study. All corpses underwent kidney biopsy performed through laparoscopy. Twenty-four operators, two per animal, performed 20 renal biopsies each (10 for each kidney), with 480 collection-procedures in total. Duration and difficulty of the procedure and the biopsy sample quality were evaluated and statistical analysis was performed using a mixed regression model with a random effect of individuals and multivariate analysis of data. There were 91.5% of the samples that were adequate for evaluation. There was no significant difference in the number of glomeruli or cortex percentage considering the attempts in either species, demonstrating the operator's ability since first collection. Swine samples showed higher amounts of renal cortex than canine samples. The procedure duration was shorter as more attempts were performed in dogs and pigs. From the fourth repetition, the professional reached a plateau for the variable related to 'collection', and from the second, the professional presented uniform duration for 'sample storage'. Operators of the swine model acquired more agility than the dog ones. The variable 'difficulty' decreased as more repetitions were performed, reaching a plateau in the sixth attempt. Seven renal biopsies laparoscopy-guided are required for an operator to be considered 'capable' to perform the procedure in the referred species included. The learning curve for image-guided kidney biopsy procedures improves the implementation of this technique and benefits patients that undergo this procedure.

Safety and utility of kidney biopsy in patients with estimated glomerular filtration rate < 30 ml/min/1.73 m2

AIM

Kidney biopsy (KBx) is the gold standard for evaluation of kidney disease, but is associated with a higher risk of complications in patients with reduced glomerular filtration rate (GFR). We studied the safety and utility of KBx in patients with eGFR <30 ml/min/1.73 m2 .

METHODS

Consecutive adult patients with eGFR <30 ml/min/1.73 m2 , who were planned for a KBx and consented to participate were prospectively enrolled. Patients with solitary/transplant kidney or acute kidney injury were excluded. Haemoglobin was checked on the day of KBx and repeated 18-24 h later along with a screening ultrasound. Post-KBx complications were noted and their risk-factors analysed. The utility of the KBx was graded as effecting significant, some, or no change to subsequent management.

RESULTS

Of the 126 patients included, 75% were male, 27.7% were diabetic, and the median eGFR was 13.5 ml/min/1.73m2 . Major complications occurred in 5.6%. Peri-renal haematomas were detected in 37.3%, and haematomas ≥2 cm were significantly more frequent in those with eGFR <15 ml/min/1.73 m2 (29.2% vs. 13%, p = .032). Dialysis was a risk factor, while pre KBx blood transfusion, diabetes and higher serum albumin were protective against any complication. KBx was more likely to make a significant difference in management in those with eGFR 15-29 ml/min/1.73m2 (44.1% vs. 11.1%, p < .001). Increasing age, lower serum creatinine and albumin were independently associated with KBx utility.

CONCLUSION

KBx is relatively safe in severe kidney disease but its risk to benefit balance needs to be carefully considered when eGFR is <15 ml/min/1.73m2 .

Tumor grade estımatıon of clear cell and papıllary renal cell carcınomas usıng contrast-enhanced MDCT and FSE T2 weıghted MR ımagıng: radıology-pathology correlatıon

BACKGROUND

Discrimination of low grade (grade 1-2) renal tumors from high grade (grade 3-4) ones carries crucial importance in terms of the management of these patients and also in the decision-making of appropriate treatment strategies. Our aim was to investigate whether contrast-enhanced multidetector computed tomography (MDCT) and T2 weighted fast spin echo (FSE) magnetic resonance imaging (MRI) could play a specific role in the discrimination of low grade versus high grade tumors in clear cell renal cell carcinoma (ccRCC) and papillary renal cell carcinoma (pRCC) patients.

METHODS

In this study, we retrospectively evaluated 66 RCC patients based on histopathologic findings who had underwent either partial or total nephrectomies. Our cohort consisted of 52 ccRCC and 14 pRCC patients, of whom 50 were male (%76) and 16 were female (%24). Among the 52 ccRCC patients, 18 had both cortico-medullary phase contrast-enhanced CT and MRI, 15 had only cortico-medullary phase CT and 19 had only MRI examination. In the pRCC group, 8 patients had both cortico-medullary phase contrast-enhanced CT and MRI, 3 had only cortico-medullary phase CT and 3 had only MRI. We both calculated mean tumor attenuation values on cortico-medullary phase MDCT images as HU (hounsfield unit) and also tumor mean signal intensity values on FSE T2 weighted MR images, using both region of interest and whole lesion measurements including normal renal cortex. The obtained values were compared with the grading results of the ccRCC and pRCC tumors according to the WHO/International Society of Urological Pathology grading system.

RESULTS

A significant positive correlation was found between the mean attenuation values of both tumor subtypes on cortico-medullary phase contrast-enhanced CT and their grades (p < 0.001). High grade tumors exhibited higher mean attenuation values (74.3 ± 22.3 HU) than the low grade tumors (55.2 ± 23.7 HU) in both subtypes. However, a statistically significant correlation was not found between the mean signal intensity values of the two tumor subtypes on FSE T2 weighted MR images and their grades (p > 0.05). Low grade tumors had a mean signal intensity value of 408.9 ± 44.6, while high grade tumors showed a value of 382.1 ± 44.2. The analysis of the ccRCC group patients, yielded a statistically significant correlation between the mean signal intensity values on T2 weighted images and tumor grading (p < 0.001). Low grade (grade 1-2) ccRCC patients exhibited higher mean signal intensity values (475.7 ± 51.3), as compared to those of high grade (grade 3-4) (418.5 ± 45.7) tumors. On the other hand, analysis of the pRCC group patients revealed that there was a significant correlation between the mean attenuation values of tumors on cortico-medullary phase contrast-enhanced CT and their grades (p < 0.001). High grade papillary subtype tumors (54.2 ± 25.2) showed higher mean attenuation values than the low grade (35.5 ± 18.8) ones.

CONCLUSIONS

Contrast-enhanced MDCT and T2 weighted FSE MRI can play a considerable role in the discrimination of low grade versus high grade tumors of both subtype RCC patients. Thus, these non-invasive evaluation techniques may have positive impact on the determination of the management and treatment strategies of these patients.

Renal transplant biopsy complications: assessment of risk factors and potential of desmopressin to decrease risk of hemorrhage

BACKGROUND

Renal transplant biopsies are essential in nephrology; however, they are invasive and complications can occur.

PURPOSE

To explore the risk of transplant kidney biopsy (TxB) complications in relation to possible preventive effects of desmopressin prophylaxis.

MATERIAL AND METHODS

A total of 515 consecutive TxB (375 patients, median age 53 years) were analyzed. In 252 TxB, the Resistive Index (RI) was measured right before the biopsy. A total of 282 patients had serum creatinine >150 µmol/L. In one of the six hospitals 39/282 patients consecutively received desmopressin (dose 0.3 µg/kg subcutaneously) as prophylaxis within 1 h before the biopsy. Fisher's exact and χ² test were used (odds ratio [OR], 95% confidence interval [CI]). Univariate and multiple binary logistic regression analyses were performed. A two-sided P value <0.05 was considered significant.

RESULTS

RI ≥ 0.8 was a risk factor for major TxB complications (OR 4.2, 95% CI 1.13-15.76). The risk for minor complications decreased with mean arterial blood pressure (MAP) (97.9 vs. 89.5 mmHg, OR 0.97, 95% CI 0.95-0.997). In a multiple regression analysis for overall biopsy complications, the risk remained increased for patients with RI ≥ 0.8 (OR 4.45, 95% CI 1.32-15.04). No patients (0/39) with desmopressin prophylaxis had a major complication versus 8/243 in the other group. In patients with serum creatinine >150 µmol/L, those with a higher MAP had more overall TxB complications (104.5 vs. 98.2 mmHg, OR 1.05, 95% CI 1.004-1.1).

CONCLUSION

RI ≥ 0.8 was a risk factor for major and overall complications and a lower MAP for minor biopsy complications. Desmopressin prophylaxis showed yet no verified benefit as prophylaxis in TxB.

Kidney biopsy in the elderly: diagnostic adequacy and yield

PURPOSE

The number of kidney biopsies (KB) performed in elderly patients has been increasing. Safety and usefulness of elderly KB have been well established, whereas much less is known about diagnostic adequacy and yield in this patient population.

METHODS

We performed a retrospective study of KBs in 428 patients from April 2015 to December 2017 at an academic institution. We compared KB from 50 patients aged over 64 (elderly) with KB from 378 patients aged between 18 and 64.

RESULTS

Gender ratio, body mass index, systolic and diastolic BP, creatinine values, incidences of AKI at the time of biopsy, INR/aptt values, and platelets were similar between the two groups. eGFR and number of transplant biopsies were lower in the elderly biopsy group. The glomerular yield was similar between the two groups (22 ± 14 vs. 22 ± 13, p = 0.869). The likelihood of obtaining more than ten glomeruli was 87% and 88%, respectively, without a significant difference. Inadequate samples were encountered in 6% of the elderly and 5.6% of the non-elderly KB, again without a significant difference. Samples taken by nephrologist had higher glomerular yield for both groups (25 ± 13 vs. 18 ± 12 overall, 26 ± 14 vs. 18 ± 14 for elderly, p < 0.001 both). Inadequate biopsies were lower in the nephrologist group when all patients were considered (3% vs. 9%, p = 0.025). Results were numerically similar for the elderly patients, but the difference was not statistically significant (2% vs. 8%, p = 0.322). No deaths occurred in both arms. Minor complications were not different for each group (4.5% vs. 4%). There were no major complications in elderly patients. However, the difference did not reach statistical significance.

CONCLUSION

The world is aging, leading to an increased number of KB in older patients. KB in the elderly is a safe, effective, and an indispensable tool for the nephrologist. This study suggests there is no need to fear lower diagnostic adequacy in the decision making of a KB for an elderly patient.

Adequacy and complication rates of percutaneous renal biopsy with 18- vs. 16-gauge needles in native kidneys in Chinese individuals

BACKGROUND

Percutaneous renal biopsy (PRB) is the primary biopsy technique and it was used by 16G needles or 18G needles in China, but there is controversy about the effect and safety of the two different diameters. The study aims to compare the adequacy, complication rate and pathological classification when using 18G vs. 16G needles to perform renal biopsy with ultrasound-guidedance on native kidneys in Chinese individuals.

METHODS

We retrospectively analyzed the number of glomeruli, adequate sample rates, complication rates and pathological classification in 270 patients with the use of 18G or 16G needles from January 2011 to May 2017 and verified whether the needle gauge affected the disease diagnosis.

RESULTS

A total of 270 kidney biopsies were performed. Among them,72 were performed with 18G needles, and 198 were performed with 16G needles. There was no difference in the number of glomeruli under light microscope using 18G relative to 16G needles (24 ± 11 vs. 25 ± 11, p = 0.265), whereas more glomeruli were found in the 16G group than in the 16G group using immunofluorescence microscopy (3 ± 2 vs. 5 ± 3, p < 0.05). There was no significant difference in the adequate sample rates between the 18G group and the 16G group (90.28% vs. 93.94%, p = 0.298). Minor complications including the incidence of lumbar or abdominal pain (4.17% vs. 7.07%, p = 0.57), gross hematuria (4.17% vs. 3.54%, p = 0.729), and perinephric hematoma without symptoms (4.17% vs. 1.52%, p = 0.195), were not significantly different between the 18G and 16G groups. In the 16G group, 2 cases of serious complications occurred: severe gross hematuria requiring blood transfusion and retroperitoneal hematoma requiring surgery. No serious complications were observed in the 18G group, although there was no significant difference in serious complications rates between the 18G and 16G groups (0% vs. 1.02%, p = 1).

CONCLUSION

There was no significant difference in the number of glomeruli, adequate sample rates, or complication rates when using 18G or 16G needles to perform renal biopsy, and the use of an 18G needle with a smaller diameter did not affect the pathological diagnosis or classification of IgA nephropathy and lupus nephritis.

Frequency, Timing, and Prediction of Major Bleeding Complications From Percutaneous Renal Biopsy

Background and Objectives:

The risk and timing of bleeding events following ultrasound-guided percutaneous renal biopsy are not clearly defined.

Design setting, participants, and measurements:

We performed a retrospective study of 617 consecutive adult patients who underwent kidney biopsy between 2012 and 2017 at a tertiary academic hospital in London, Canada. We assessed frequency and timing of minor (not requiring intervention) and major (requiring blood transfusion, surgery, or embolization) bleeds and developed a personalized risk calculator for these.

Results:

Bleeding occurred in 79 patients (12.8%; 95% confidence interval [CI]: 10.4%-15.7%). Minor bleeding occurred in 67 patients (10.9%; 95% CI: 8.6%-13.6%). Major bleeding occurred in 12 patients (1.9%; 95% CI: 1.1%-3.4%); 2 required embolization or surgery (0.3%; 95% CI: 0.09%-1.2%) and 10 required blood transfusion (1.6%; 95% CI: 0.9%-3.0%). Seventy-three of 79 events were identified immediately on post-procedure ultrasound (92.4% of cases; 95% CI: 84.4%-96.5%). Four of 617 patients experienced a minor event not detected immediately (0.6%; 95% CI: 0.3%-1.7%). Two patients (0.3%; 95% CI: 0.09%-1.2%) suffered a major complication that was not recognized immediately; both required blood transfusions only. There were no deaths or nephrectomies. A risk calculator using age, body mass index, platelet count, hemoglobin concentration, size of the target kidney, and whether the kidney is native, or an allograft predicted minor (C-statistic, 0.70) and major bleeding (C-statistic, 0.83).

Conclusions:

This retrospective study of 617 patients who had percutaneous ultrasound-guided renal biopsies supports the safety of short post-biopsy monitoring for most patients. A risk calculator can further personalize estimates of complication risk (http://perioperativerisk.com/kbrc).

Bleeding Complications After Percutaneous Native Kidney Biopsy: Results From the Boston Kidney Biopsy Cohort

Background

The major risk of kidney biopsy is severe bleeding. Numerous risk factors for bleeding after biopsy have been reported, but findings have been inconsistent.

Methods

We retrospectively reviewed medical records of adult patients enrolled in a native kidney biopsy cohort study to identify major bleeding events (red blood cell [RBC] transfusions, invasive procedures, kidney loss, or death). We used logistic and linear regression models to identify characteristics associated with postbiopsy RBC transfusions and decline in hemoglobin within a week after the procedure.

Results

Major bleeding events occurred in 28 of 644 (4.3%) patients (28 required an RBC transfusion, 4 underwent angiographic intervention, and 1 had open surgery to control bleeding). No patient lost a kidney or died because of the biopsy. Postbiopsy RBC transfusion risk was driven by the baseline hemoglobin level (odds ratio [OR] 13.6; 95% confidence interval [CI] 5.4–34.1 for hemoglobin <10 vs. ≥10 g/dl). After adjusting for hemoglobin, no other patient characteristics were independently associated with RBC transfusions. Female sex (β = 0.18; 95% CI: 0.04–0.32), estimated glomerular filtration rate (eGFR) <30 ml/min per 1.73 m² (β = 0.32; 95% CI: 0.14–0.49), and baseline hemoglobin (β = 0.09; 95% CI: 0.05–0.13, per g/dl increase) were independently associated with a larger drop in hemoglobin. Histopathologic lesions were not independently associated with major bleeding after biopsy.

Conclusion

Biopsies were generally well tolerated. Baseline hemoglobin was the dominant risk factor for RBC transfusions, but female sex and eGFR <30 ml/min per 1.73 m² were also associated with a larger decline in hemoglobin after the procedure.

Diffusion Weighted Magnetic Resonance Imaging in the Assessment of Renal Function and Parenchymal Changes in Chronic Kidney Disease: A Preliminary Study

Background

The aim of this study was to evaluate the feasibility of using intravoxel incoherent motion (IVIM) imaging for noninvasive assessment of pathologic changes in chronic kidney disease (CKD).

Material/Methods

Thirty-four patients with CKD and 20 healthy volunteers were examined on a 1.5 T magnetic resonance imaging (MRI) unit. The examination consisted of morphologic sequences and diffusion-weighted echo-planar sequence with 10 b values. Diffusion parameters were calculated with the use of mono- (apparent diffusion coefficient, ADC) and bi-exponential model: pure diffusion coefficient (D) and perfusion fraction (Fp). Blood samples to assess the serum creatinine level were taken immediately before examination. Ultrasound guided biopsies were performed in less than 30 days from MRI and were scored by an experienced nephropathologist. Parametrical unpaired t-test and ROC curve analysis were used to investigate differences in diffusion parameters in relation to estimated glomerular filtration rate (eGFR). Pearson’s correlation coefficients were calculated to assess relationship between diffusion parameters and laboratory and histopathological markers of renal damage. P-value <0.05 indicated statistical significance.

Results

Both ADC and D correlated positively with eGFR (respective r 0.74 and 0.72), however D showed a more significant correlation with histopathology: while D correlated negatively with parameters reflecting chronic glomerular (r −0.48) and tubulo-interstitial changes (r −0.47), ADC correlated only with interstitial infiltrations (r −0.44). Flow-related diffusion parameters showed high standard deviation.

Conclusions

IVIM imaging is sensitive to functional and morphologic changes in CKD. The separation of influence of Fp from true diffusion improves the assessment of chronic changes in renal parenchyma.

Risk Factors Associated with Major Complications after Ultrasound-Guided Percutaneous Renal Biopsy of Native Kidneys

INTRODUCTION

Percutaneous renal biopsy (PRB) of native kidneys is an important tool for diagnosis and management of renal disease. In this study, we analyzed the success, safety, and risk complications of PRB in our center.

METHODS

A retrospective review of ultrasound-guided PRB done at our institution from January 1998 to December 2017 was performed. Clinical and laboratory data were collected for 661 PRBs. Statistical analysis was performed using the Mann-Whitney U test for continuous variable and chi-square test for categorical variables. Multivariate analysis using logistic regression was performed to assess factors associated with increased risk of complications after PRB.

RESULTS

The median age was 56 (42-68) years old, the majority were male (64%) and white (82%). Ten glomeruli were present in 63.5% of PRBs. Overall, the rate of complications was 16.6%, where 15.1% of them were minor complications and 1.5% were major complications. Perinephritic hematoma accounted for the minor complication that occurred most frequently, whereas the need of a blood transfusion was the prevalent for major complications. By multivariate analysis, increased activated partial thromboplastin time (aPTT; OR 1.11, 95% CI 1.035-1.180) and prebiopsy lower hemoglobin (Hgb; OR 1.61, 95% CI 1.086-2.304) were identified as independent risk factors for major complications. In addition, older patients (OR 1.057, 95% CI 1.001-1.117) were identified as an independent risk factor for blood transfusion requirement.

CONCLUSION

The current risk of complications after native PRB is low. Major complications are most common in case of increased aPTT and decreased Hgb baseline level.

Clinical parameters predicting complications in native kidney biopsies

Background

Renal biopsies are essential in nephrology but they are invasive and complications can occur. The aim of this study was to explore clinical parameters that can be used as predictors for biopsy complications.

Methods

Clinical parameters such as demographics, biopsy indications, serology, comorbidities and clinical chemistry were retrieved from a regional biopsy registry between 2006 and 2015 and from a nationwide registry between 2015 and 2017. Clinical data before biopsy were compared with data on major biopsy complications. Fisher’s exact and χ² tests were used and odds ratios (ORs) with 95% confidence intervals (CIs) were presented. Univariate and multiple binary logistic regression analyses were performed with complications as outcome. A two-sided P-value <0.05 was considered significant.

Results

In total, 2835 consecutive native kidney biopsies were analysed (39% women and 61% men, median age 57 years). No death and nephrectomy due to biopsy complications were registered. The frequency of major biopsy complications was 5.65%. In the multiple logistic regression, the risk for complications increased in women [OR 1.51 (95% CI 1.08–2.11)] and decreased with age: 45–64 years age group [OR 0.66 (95% CI 0.44–0.99)] and >74 years age group [OR 0.51 (95% CI 0.27–0.96)]. Among comorbidities, patients with diabetes mellitus type 2 [OR 2.07 (95% CI 1.15–3.72)] and non-ischaemic heart disease [OR 3.20 (95% CI 1.64–6.25)] had a higher risk for major biopsy complications.

Conclusions

Female gender, younger age (≤44 years), diabetes mellitus type 2 and non-ischaemic heart disease were found as risk factors for major biopsy complications.

Association of Serum Uromodulin With ESKD and Kidney Function Decline in the Elderly: The Cardiovascular Health Study

RATIONALE & OBJECTIVE

Uromodulin is released by tubular epithelial cells into the serum and lower levels are associated with more severe interstitial fibrosis and tubular atrophy. Low serum uromodulin (sUMOD) levels are associated with mortality and cardiovascular disease. However, little is known about the association of sUMOD levels with long-term kidney outcomes in older adults, a population with a high prevalence of interstitial fibrosis and tubular atrophy.

STUDY DESIGN

Case-cohort study and case-control study.

SETTING & PARTICIPANTS

Random subcohort (n=933) and additional cases of end-stage kidney disease (ESKD) and kidney function decline (≥30% decline in estimated glomerular filtration rate [eGFR]) during follow-up of the Cardiovascular Health Study (CHS).

PREDICTOR

sUMOD level.

OUTCOMES

ESKD (n=14) from the random subcohort and all additional ESKD cases from outside the random subcohort (n=39) during follow-up (10 years, case-cohort study); kidney function decline of≥30% eGFR at 9 years of follow-up in individuals with repeated eGFR assessments from the random subcohort (n=56) and additional cases (n=123). 224 participants from the random subcohort served as controls (case-control study).

ANALYTICAL APPROACH

Modified multivariable Cox regression for ESKD and multivariable logistic regression for kidney function decline. Both analyses adjusted for demographics, eGFR, urinary albumin-creatinine ratio, and other kidney disease progression risk factors.

RESULTS

Mean age of the random subcohort was 78 years, 40% were men, 15% were black. Mean sUMOD level was 127±64ng/mL and eGFR was 63±19mL/min/1.73m2. In multivariable analysis, each 1-SD higher sUMOD level was associated with 63% lower risk for ESKD (HR, 0.37; 95% CI, 0.14-0.95). In demographic-adjusted analyses of kidney function decline, each 1-SD higher sUMOD level was associated with 25% lower odds of kidney function decline (OR, 0.75; 95% CI, 0.60-0.95); after multivariable adjustment, the association was attenuated and no longer significant (OR, 0.88; 95% CI, 0.68-1.14).

LIMITATIONS

Possibility of survival bias in the kidney function decline analysis.

CONCLUSIONS

Higher sUMOD levels may identify elderly persons at reduced risk for ESKD.

The efficacy of blind versus real-time ultrasound-guided percutaneous renal biopsy in developing country

Introduction:

Renal biopsy is a useful diagnostic procedure. In developing countries, two techniques of renal biopsy, blind percutaneous renal biopsy and real-time ultrasound-guided percutaneous renal biopsy, have been performed. The majority of studies compared these using different types and sizes of biopsy needle. The aim of this study was to compare both techniques in resource constraint country.

Method:

We reviewed renal biopsy database, between 1 January 2014 to 30 June 2017. The primary outcome was the total number of glomeruli. The other outcomes were tissue adequacy and bleeding complications. We also analyzed multivariable logistic regression to find factors associated with tissue adequacy and bleeding complications.

Result:

Of the 204 renal biopsies, 100 were blind percutaneous renal biopsy and 104 real-time ultrasound-guided percutaneous renal biopsy. The number of native renal biopsies was 169 (82.8%). Baseline characteristics of two groups were comparable. The mean number of total glomeruli from real-time ultrasound-guided percutaneous renal biopsy was significantly more than blind percutaneous renal biopsy (20.8 ± 12.1 vs 16.0 ± 13.0, p = 0.001). The real-time ultrasound-guided percutaneous renal biopsy obtained more adequate tissues than blind percutaneous renal biopsy (45.2% vs 16%, p < 0.001) and was the only factor associated with adequate tissue. Moreover, 16 renal biopsies from blind percutaneous renal biopsy obtained inadequate tissue. The overall bleeding complications were not statistically different. We found being female, lower eGFR and lower hematocrit were associated with bleeding complications.

Conclusion:

In comparison with blind percutaneous renal biopsy, real-time ultrasound-guided percutaneous renal biopsy obtained more adequate tissue and number of glomeruli. While the complications of both were comparable. We encourage to practice and perform real-time ultrasound-guided percutaneous renal biopsy in resource constraint countries.

Prediction of ISUP grading of clear cell renal cell carcinoma using support vector machine model based on CT images

BACKGROUND

To explore whether radiomics combined with computed tomography (CT) images can be used to establish a model for differentiating high grade (International Society of Urological Pathology [ISUP] grade III-IV) from low-grade (ISUP I-II) clear cell renal cell carcinoma (ccRCC).

METHODS

For this retrospective study, 3-phase contrast-enhanced CT images were collected from 227 patients with pathologically confirmed ISUP-grade ccRCC (155 cases in the low-grade group and 72 cases in the high-grade group). First, we delineated the largest dimension of the tumor in the corticomedullary and nephrographic CT images to obtain the region of interest. Second, variance selection, single variable selection, and the least absolute shrinkage and selection operator were used to select features in the corticomedullary phase, nephrographic phase, and 2-phase union samples, respectively. Finally, a model was constructed using the optimal features, and the receiver operating characteristic curve and area under the curve (AUC) were used to evaluate the predictive performance of the features in the training and validation queues. A Z test was employed to compare the differences in AUC values.

RESULTS

The support vector machine (SVM) model constructed using the screening features for the 2-stage joint samples can effectively distinguish between high- and low-grade ccRCC, and obtained the highest prediction accuracy. Its AUC values in the training queue and the validation queue were 0.88 and 0.91, respectively. The results of the Z test showed that the differences between the 3 groups were not statistically significant.

CONCLUSION

The SVM model constructed by CT-based radiomic features can effectively identify the ISUP grades of ccRCC.

Lumbar Artery Bleed as a Complication of Percutaneous Renal Biopsy and a Proposed Workflow for Massive Bleeding

Injuries to extrarenal arteries caused by percutaneous biopsy needles are very rare but highly lethal due to delay in recognition. Here we report the case of an inadvertent lumbar artery puncture after native renal biopsy and provide a literature review and a proposed workflow for management of massive bleed after renal biopsy. This case highlights evidence-based management considerations regarding massive bleed after renal biopsy, including the first-line imaging modality and the need to consider extrarenal site bleed. While angiographic embolization is an effective method of control of haemorrhage, surgical exploration is required in a proportion of cases for control of bleeding. Centre-specific workflows should be adopted to minimize the mortality and morbidity associated with massive bleed after renal biopsy.

Simple risk score for prediction of haemorrhagic complications after a percutaneous renal biopsy

AIM

To derive a simple risk score to predict the individual risk of major complications for patients undergoing a percutaneous renal biopsy procedure of native kidneys.

METHODS

The risk score was derived from a cohort of 1205 adult patients subjected to percutaneous renal biopsy and assigned to training and validation datasets. Factors associated with major complications were derived from univariate analysis and then modelled by stepwise multivariate logistic regression. Based on the odds ratio, independent predictors were assigned a weighted integer. The risk score is calculated from the sum of the integers.

RESULTS

The overall incidence of major complications was 3.2%. Independent factors associated with MC were lower pre-biopsy haemoglobin, lower platelets, higher blood urea nitrogen, documented chronic kidney disease features in pre-biopsy ultrasound (US) and the presence of haematoma in the post-biopsy US. A score for pre-biopsy evaluation included the first four predictors and stratified patients in three categories with increasing risk at higher scores (low-risk 0.1%, moderate-risk 3.0% and high-risk 26.1%). The score demonstrated good discriminative power (AUC = 0.872). The addition of post-biopsy US findings increased the discriminative power (AUC = 0.938). A higher post-biopsy risk score was also associated with a higher incidence of MC (low-risk 0.2%, moderate-risk 2.7%, high-risk 16.9%).

CONCLUSION

The risk of major complications after a percutaneous renal biopsy can be assessed by a simple risk score calculated from readily available information.

Desmopressin (Octostim®) before a native kidney biopsy can reduce the risk for biopsy complications in patients with impaired renal function: A pilot study

AIM

To evaluate whether the administration of desmopressin alters the risk for renal biopsy complications.

METHODS

A multicenter registry containing 576 native kidney biopsies (NKb) with a serum creatinine above 150 μmol/L in 527 patients (372 men and 155 women, median age 61 years) was used. Most of the data were prospective. At one of the hospitals all biopsies with creatinine above 150 μmol/L received desmopressin before biopsies (NKb 204). These were compared to outcome of biopsy complications against other centres where desmopressin was not given (NKb 372). Fisher's exact test, χ² analyses, univariate and multiple binary logistic regression were used. Data were given as odds ratio (OR) and confidence interval (CI). A two sided P-value of <0.05 was considered significant.

RESULTS

In NKb with creatinine >150 μmol/L, those with desmopressin had less overall (3.4% vs 8.4%, OR 0.39, CI 0.17-0.90) whereas major or minor complications were not different. While desmopressin did not exhibit difference in complications in men, women received less major (0% vs 8.6%, P = 0.03) and overall complications (0% vs 12.1%, P = 0.006). A multiple logistic regression revealed that, after adjusting for BMI, age and sex, prophylaxis with desmopressin showed less major (OR 0.38, CI 0.15-0.96) and overall complications (OR 0.36, CI 0.15-0.85).

CONCLUSION

Desmopressin given before a native kidney biopsy in patients with impaired renal function can reduce the risk for complications.

Comparison of native and transplant kidney biopsies: diagnostic yield and complications

Background

The safety and adequacy are established for the native percutaneous renal biopsy (PRB) but no prospective studies exist that directly compare these with transplant PRB.

Methods

From 1995 to 2015, 1705 adults underwent percutaneous native [native renal biopsy (NRB)] or transplant renal biopsy (TRB) by the Nephrology service. Real-time ultrasound and automated biopsy needles (NRB, 14 or 16 gauge; TRB, 16 gauge) were used. Patients were observed for 24 h (NRB) or 8 h (TRB) post-procedure. Adequacy was defined as tissue required for diagnosis plus glomerular yield. Complications were defined as those resulting in the need for an intervention, such as surgery, interventional radiologic procedure, readmission, blood transfusion and death. Data were collected prospectively in all biopsies.

Results

At the time of biopsy, NRB patients were younger (mean ± SD, 47 ± 17 versus 50 ± 14 years, P < 0.0001) and more often female (62 versus 48%, P < 0.0001) compared with TRB. A fellow supervised by an attending performed the procedure in 91% of NRB compared with 63% of TRB (P < 0.0001). TRB patients were more hypertensive [systolic blood pressure (SBP) 140 ± 22 versus 133 ± 18 mmHg, P < 0.0001] and had a higher serum creatinine (3.1 ± 1.8 versus 2.3 ± 2.2 mg/dL, P < 0.0001), activated partial thromboplastin time (28 ± 4.3 versus 27 ± 5 s, P < 0.0001) as well as lower hemoglobin (Hgb) (11.2 ± 1.8 versus 11.7 ± 2.1 g/dL, P < 0.0001) compared with NRB. Adequate tissue for diagnosis was obtained in > 99% of NRB and TRB (P = 0.71). Compared with TRB, NRB had a greater drop in Hgb after the biopsy (0.97 ± 1.1 versus 0.73 ± 1.3 g/dL, P < 0.0001), a higher complication rate (6.5 versus 3.9%, P = 0.02) and higher transfusion rate (5.2 versus 3.3%, P = 0.045). There was one death in each group attributed to the biopsy.

Conclusions

Although death is equally rare, the complication rate is higher in NRB compared with TRB despite TRB having more of the traditional risk factors for bleeding. Differences in technique, operator (fellow or attending) or needle gauge may explain this variability.

Short-term complications for percutaneous ultrasound-guided biopsy of renal masses in adult outpatients

Background Ultrasound-guided percutaneous kidney tumor biopsy (UGPKB) plays an important role in the diagnosis of renal tumor but there are no consensuses with respect to the length and the extend of the post-biopsy observation period. Purpose To assess the short-term complication rate after UGPKB and to evaluate whether the onset of complications allows for the procedure to be performed in an outpatient setting with same-day discharge. Material and Methods Between March 2012 and March 2014, a total of 287 UGPKB were performed in an outpatient setting at a Danish university referral center. All patient records were retrospectively reviewed and post-biopsy complications as well as biochemical parameters were registered. Results The overall complication rate was 3.8% (11 patients). Major complications occurred in 1.0% of all cases (three patients); one patient with ongoing bleeding that required intervention and two patients with septicemia. Minor complications occurred in 2.8% of cases (eight patients); six patients with self-limiting gross hematuria, one patient with small asymptomatic subcapsular hematoma, and one patient with vasovagal syncope. The timing of both minor and major complication onset ranged from the time of biopsy and up to four days after discharge. Conclusion UGPKB of indeterminate renal masses in adult patients in an outpatient setting appears to be a safe procedure with a very low rate of major complications. Same-day discharge after renal mass biopsy seems feasible.

Bleeding complications post ultrasound guided renal biopsy - A single centre experience from Pakistan

INTRODUCTION

Renal biopsy is the diagnostic modality of choice for the diagnosis of renal parenchymal diseases. The advent of improved imaging techniques and biopsy needles over the years has increased the safety of the procedure and the ability to obtain adequate renal tissue for diagnosis. However, there is paucity of data in this regard from Pakistan. This study shall help in establishing the local perspective of the frequency of bleeding complications in percutaneous ultrasound guided renal biopsy.

MATERIALS AND METHODS

This is a prospective case series of hospitalized patients from January till December 2015 at Nephrology Department, Aga Khan University Hospital, Karachi, Pakistan. After enrolment, each participant was followed for 24 h after renal biopsy.

RESULTS

A total of 220 patients were included. Mean age was 41.65 ± 8.627 years, 82 (37.2%) were male and 138 (62.8%) were female. Pre and post biopsy haemoglobin, pre and post biopsy haematocrit were 10.92 ± 1.25 and 10.60 ± 1.22, and 30.82 ± 4.73 and 30.49 ± 4.68 respectively. Out of 220 patients, 16 (7.27%) developed major complications and 26 (11.8%) developed minor complications in 24 h after renal biopsy.

CONCLUSIONS

Percutaneous kidney biopsy is a relatively safe procedure. Complication rates following the procedure are minimal. It is important that all nephrology programs train the trainees in performing biopsies, so that there is a wider clinical use of this important investigation even in underprivileged & developing countries.

Sixteen Gauge biopsy needles are better and safer than 18 Gauge in native and transplant kidney biopsies

Background Kidney biopsies are essential for optimal diagnosis and treatment. Purpose To examine if quality and safety aspects differ between types and sizes of biopsy needles in native and transplant kidneys. Material and Methods A total of 1299 consecutive biopsies (1039 native and 260 transplant kidneys) were included. Diagnostic quality, needle size and type, clinical data and complications were registered. Eight-three percent of the data were prospective. Results In native kidney biopsies, 16 Gauge (G) needles compared to 18 G showed more glomeruli per pass (11 vs. 8, P <  0.001) with less complications. Sub-analysis in native kidney biopsies revealed that 18 G 19-mm side-notch needles resulted in more major (11.3% vs. 3%; odds ratio [OR], 4.1; 95% confidence interval [CI], 1.4-12.3) and overall complications (12.4% vs. 4.8%; OR, 2.8; 95% CI, 1.1-7.1) in women than in men. If the physician had performed less compared to more than four native kidney biopsies per year, minor (3.5% vs. 1.4%; OR, 2.6; 95% CI, 1.1-6.2) and overall complications (11.5% vs. 7.4%; OR, 1.6; 95% CI, 1.1-2.5) were more common. In transplant kidney biopsies, 16 G needles compared to 18 G resulted in more glomeruli per pass (12 vs. 8, P <  0.001). No differences existed in frequency of biopsy complications. The localization of performing biopsies was not a risk factor to develop complications. Conclusion Kidney biopsies taken by 16 G needles result in better histological quality and lower frequency of complications compared to 18 G. For native kidney biopsies the performer of the biopsy should do at least four biopsies per year.

Achieving Procedural Competence during Nephrology Fellowship Training: Current Requirements and Educational Research

Concerns have previously been raised as to whether training programs are ensuring that nephrology fellows achieve competence in the procedural skills required for independent practice. We sought to review the current requirements for procedural training as well as educational research pertaining to achieving competence in the core nephrology procedures of nontunneled (temporary) hemodialysis catheter insertion and percutaneous kidney biopsy. At this time, there is no universal approach to procedural training and assessment during nephrology fellowship. Nonetheless, simulation-based mastery learning programs have been shown to be effective in improving fellows' skills in nontunneled (temporary) hemodialysis catheter insertion and should be provided by all nephrology training programs. For percutaneous kidney biopsy, the development and evaluation of inexpensive simulators are a promising starting point for future study. Current practice with respect to procedural training during nephrology fellowship remains imperfect; however, the ongoing shift toward competency-based evaluation provides opportunities to refocus on improvement.

High Resistive Index in Transplant Kidneys Is a Possible Predictor for Biopsy Complications

BACKGROUND

Transplant kidney biopsies are performed to determine a histological diagnosis for specific patient treatment. The aim of this study was to investigate if Resistive Index (RI) could be a predictor for biopsy complications.

METHODS

In this study, 220 consecutive transplant kidney biopsies (136 men and 84 women; median age, 55.5 years) were prospectively included. RI (median, 0.7) was measured by use of ultrasound. Histological diagnoses and biopsy complications were registered. Biopsy needles were either 16- or 18-gauge. Biopsies were performed by radiologists and were carried out as an outpatient procedure (70%) or an inpatient procedure (30%). Usually three passes per biopsy were performed.

RESULTS

The overall complication rate was 6.8%, divided into major (4.5%) and minor (2.3%) complications. An RI ≥0.8 predicts major (13.3% versus 3.2%; risk ratio [RR], 4.2; confidence interval [CI], 1.3-14.1; P = .03) and overall biopsy complications (16.7% versus 5.3%; RR, 3.2; CI, 1.2-8.6; P = .04) compared with RI <0.8. In the group <0.8, RI correlated with age (r_s = 0.28, P < .001) and systolic blood pressure (r_s = 0.18, P = .02). In the group ≥0.8, RI correlated with degree of interstitial fibrosis (r_s = 0.65, P = .006) and systolic blood pressure (r_s = 0.40, P = .03). The multiple regression analysis showed that in the group <0.8, the RI correlated only with age (P < .001), whereas in the group ≥0.8, RI correlated only with the degree of interstitial fibrosis (P = .003).

CONCLUSIONS

An RI ≥0.8 indicates greater risk for major and overall biopsy complications and should result in greater caution after biopsy.

Renal Medullary and Cortical Correlates in Fibrosis, Epithelial Mass, Microvascularity, and Microanatomy Using Whole Slide Image Analysis Morphometry

Renal tubulointerstitial injury often leads to interstitial fibrosis and tubular atrophy (IF/TA). IF/TA is typically assessed in the renal cortex and can be objectively quantitated with computerized image analysis (IA). However, the human medulla accounts for a substantial proportion of the nephron; therefore, medullary scarring will have important cortical consequences and may parallel overall chronic renal injury. Trichrome, periodic acid-Schiff (PAS), and collagen III immunohistochemistry (IHC) were visually examined and quantitated on scanned whole slide images (WSIs) (N = 67 cases). When tuned to measure fibrosis, IA of trichrome and Trichrome-PAS (T-P) WSIs correlated for all anatomic compartments (among cortex, medulla, and entire tissue, r = 0.84 to 0.89, P all <0.0001); and collagen III deposition correlated between compartments (r = 0.69 to 0.89, P <0.0001 to 0.0002); however, trichrome and T-P measures did not correlate with collagen deposition, suggesting heterogeneous contributions to extracellular matrix deposition. Epithelial cell mass (EPCM) correlated between cortex and medulla when measured with cytokeratin IHC and with the trichrome red portion (r = 0.85 and 0.66, respectively, all P < 0.0001). Visual assessment also correlated between compartments for fibrosis and EPCM. Correlations were found between increasing medullary inner stripe (IS) width and fibrosis in all of the tissue and the medulla by trichrome morphometry (r = 0.56, P < 0.0001, and r = 0.48, P = 0.00008, respectively). Weak correlations were found between increasing IS width and decreasing visual assessment of all tissue EPCM. Microvessel density (MVD) and microvessel area (MVA) measured using a MVD algorithm applied to CD34 IHC correlated significantly between all compartments (r = 0.76 to 0.87 for MVD and 0.71 to 0.87 for MVA, P all < 0.0001). Overall, these findings demonstrate the interrelatedness of the cortex and medulla and the importance of considering the renal parenchyma as a whole.

Clinical factors influencing the decision to transfuse after percutaneous native kidney biopsy

Background

Transfusion of erythrocytes is the most common intervention after a complicated percutaneous renal biopsy (PRB). Anemia is considered to be a leading risk factor for bleeding following a PRB, and based on recent studies of transfusions in hospitalized patients, many institutions are restricting the threshold for erythrocyte transfusion to a lower hemoglobin concentration (Hgb). The purpose of this study is to analyze factors that influence the transfusion decision after a PRB, and to determine whether anemia is truly a risk factor for bleeding or anemic patients are simply more likely to receive a transfusion because of their already lower pre-PRB Hgb.

Methods

PRB of native kidneys was performed using real-time ultrasound with automated biopsy needles from January 1990 to April 2014. All patients were prospectively followed for bleeding with a 24-h inpatient observation. An intervention for a bleeding complication (BL-I) was defined by undergoing a procedure (cystoscopy, embolization), receiving a blood transfusion (BL-T), death and/or readmission related to the biopsy. To further define the effect of anemia, patients were divided into three pre-PRB Hgb groups: <9.0 g/dL (n = 79), 9.0–11.0 g/dL (n = 266) and >11.0 g/dL (n = 565).

Results

BL-I occurred in 71/910 (7.8%) of PRBs. The majority of these were BL-T (57/71, 80%; 57/910, 6.3% overall). Patients with BL-I had lower pre-PRB Hgb than those without BL-I (mean ± SD; 10.3 ± 2.0 versus 12.0 ± 2.1 g/dL, P < 0.0001) and a greater change (Δ) in Hgb (2.1 ± 1.6 versus 1.0 ± 0.8 g/dL, P < 0.0001). When compared with higher Hgb, patients with Hgb <9.0 g/dL had more traditional risk factors for bleeding (older age: 49 ± 18 versus 48 ± 18 versus 45 ± 16 years, P = 0.02; female: 72 versus 70 versus 56%, P < 0.0001; higher serum creatinine: 4.0 ± 2.9 versus 2.9 ± 2.6 versus 1.7 ± 1.4 mg/dL, P < 0.0001; higher systolic blood pressure: 138 ± 18 versus 133 ± 19 versus 133 ± 18 mmHg, P = 0.06; higher bleeding time: 7.6 ± 1.8 versus 7.4 ± 2.0 versus 6.7 ± 1.8 min, P < 0.0001). When BL-T was stratified by pre-PRB Hgb, there were more transfusions in those with lower pre-PRB Hgb (24 versus 9 versus 3%, P < 0.0001). However, these patients not only had fewer hematomas (58 versus 83 versus 87%, P = 0.04) but also demonstrated a smaller ΔHgb post-PRB (1.3 ± 1.0 versus 1.8 ± 0.8 versus 3.2 ± 1.6, P < 0.0001) compared with patients with higher pre-PRB Hgb, yet still received a transfusion.

Conclusions

While patients with lower pre-PRB Hgb have more of the traditional risk factors for a complication after PRB, there was actually less clinically evident bleeding in these patients who were transfused. Although anemia itself has been considered to be a risk factor for a complication in the past, it more accurately represents only a predictor of receiving an erythrocyte transfusion. In the setting of the PRB, the decision for transfusion is influenced more by the severity of anemia at baseline as opposed to clinically evident bleeding.

Hemorrhage from lumbar artery following percutaneous renal biopsy

We present a 58-year-old lady who underwent ultrasound-guided renal biopsy for suspected acute glomerulonephritis. Within minutes, the radiologist noticed an echogenic band around left kidney and in the muscular planes. Computerized tomography revealed focal active contrast extravasation from arcuate or interlobular artery in lower pole of left kidney and lumbar artery at third lumbar vertebra. The bleeding vessel was occluded with gelfoam.

Increased risk of renal biopsy complications in patients with IgA-nephritis

BACKGROUND

The aim of this study was to investigate if specific clinical and histological findings can be related to biopsy complications to enable more closely monitoring patients at high risk.

METHODS

Results from 1081 biopsies (994 patients, median age 54.5 years; 896 native and 185 transplant kidney biopsies) were included. Diagnostic quality, morphology, clinical data and complications were prospectively registered.

RESULTS

In native kidney biopsies, the most common diagnosis was IgA-nephritis, while in transplant kidney biopsies it was rejection. Patients with IgA-nephritis had a higher risk of major complications (11.7 versus 6.4 %, Odds Ratio (OR) 1.8, Confidence Interval (CI) 1.1-3.2) when compared to patients with other diseases. In native kidney biopsies, patients who experienced major complications had higher degrees of glomerulosclerosis (31 versus 20 %, p = 0.008), whereas in transplant kidney biopsies, patients had higher degrees of interstitial fibrosis (82 versus 33 %, p < 0.001) when compared to patients without major complications. IgA-nephritis-patients had a higher risk of re-biopsies (4.7 versus 1.3 %, OR 4, CI 1.5-11) than patients with other diseases. Patients with native kidneys who needed re-biopsies were younger (42.6 versus 52.3 years, p = 0.031) and had a higher degree of interstitial fibrosis (63 versus 34 %, p = 0.046).

CONCLUSIONS

Patients with IgA-nephritis have an increased risk of major biopsy complications. The risk of re-biopsies was higher in younger individuals and in patients with IgA-nephritis.

Resolution of proteinuria after transarterial embolization of aberrant renal artery in a patient with focal segmental glomerulosclerosis

A 24-year-old man was admitted to our hospital for persistent proteinuria. He was born with a low birth weight but had grown up uneventful until the age of 20 when he was found to have proteinuria. Because his body mass index was 30.9 kg/m² at that time, he was diagnosed as obesity-related nephropathy. However, weight reduction and administration of ACE inhibitor were minimally effective for the amelioration of proteinuria. Ultrasound-guided percutaneous renal biopsy at the lower pole of right kidney was performed. As serious bleeding occurred from the right aberrant renal artery soon after biopsy, he was treated with transarterial embolization (TAE). The day after TAE, proteinuria completely disappeared. Renal biopsy showed benign nephrosclerosis with secondary focal segmental glomerulosclerosis (FSGS). Proteinuria could be induced by increased blood flow and pressure due to abnormal blood supply from aberrant renal artery. This is the first report of resolution of proteinuria after TAE of aberrant renal artery in a patient with FSGS.

Renal biopsy with 16G needle: a safety study

INTRODUCTION AND OBJECTIVE

The development of percutaneous renal biopsy as a routinary diagnostic procedure for renal masses is topic of discussion for the last few years. However, this technique has been associated with some complications, although infrequent, and morbidity. Our objective is to carry out a descriptive study about complications and outcomes of orthotopic kidney biopsies with 16 G needle.

MATERIAL AND METHODS

A retrospective review of 180 orthotopic ultrasound-guided renal biopsies performed in our service among January 2008 to May 2010 was carried out. The procedure was developed using an automated biopsy gun (16G needle). Multiple clinical variables, early post-procedure complications and its management were collected. Complication rates as well as the relationship between risk factors and occurrence of complications were studied.

RESULTS

Mean age was 55.8 years. The average number of biopsy cylinders per intervention was 2.49. The overall complication rate was 5.6%. An interventionist attitude derived from complication of the procedure was necessary in only 3 patients (1.67%). No surgical interventions were required and no death as consequence of procedure was registered. No relationship between hypertension (P=.09) previous anticoagulation (P=.099) or previous antiaggregation (P=.603) and complications were demonstrated. In 2.8% of biopsies the material obtained was insufficient for diagnosing.

CONCLUSIONS

Percutaneous ultrasound-guided renal biopsy with 16G needle is a safe technique with high diagnostic performance.

A study of clinical complications and risk factors in 1,001 native and transplant kidney biopsies in Sweden

BACKGROUND

In Sweden, native and transplant kidney biopsies are usually performed in major renal medical centers.

PURPOSE

To clarify risk factors in native and transplant kidney biopsies to improve patient safety.

MATERIAL AND METHODS

A total of 1001 biopsies (in 352 women and 565 men) were included. The median age was 54 years (range, 16-90 years). Data were derived from 826 native kidney biopsies (640 prospective and 186 retrospective) and 175 transplant kidney biopsies (170 prospective and 5 retrospective). Various factors and complications were registered while performing native and transplant kidney biopsies, focusing on major (e.g. blood transfusions, invasive procedures) and minor complications. The prospective protocol was used at six centers and at one center data were obtained retrospectively.

RESULTS

Women were at greater risk of overall complications than men (12.2% vs. 6.5%; P = 0.003; odds ratio [OR], 2.0; confidence interval [CI], 1.3-3.1) as well as of major complications (9.6% vs. 4.5%; P = 0.002; OR, 2.2, CI 1.3-3.7). Major complications occurred more commonly after biopsies from the right kidney, in women than in men (10.8% vs. 3.1%; P = 0.005; OR, 3.7; CI, 1.5-9.5), and in patients with lower BMI (25.5 vs. 27.3, P = 0.016) and of younger age (45 years vs. 52.5 years; P = 0.001). Lower mean arterial pressure in transplant kidney biopsies indicated a risk of major complications (90 mmHg vs. 98 mmHg; P = 0.039). Factors such as needle size, number of passes, serum creatinine, and eGFR did not influence complication rates.

CONCLUSION

The present findings motivate greater attention being paid to the risk of major side-effects after right-side biopsies from women's kidneys, as well as after biopsies from younger patients and patients with lower BMI.