Risk of percutaneous renal biopsy of native kidneys in the evaluation of acute kidney injury

Noninvasive Diagnosis of Kidney Dysfunction Using a Small-Molecule Manganese-Based Magnetic Resonance Imaging Probe

Contrast-enhanced magnetic resonance imaging (CE-MRI) is a promising approach for the diagnosis of kidney diseases. However, safety concerns, including nephrogenic systemic fibrosis, limit the administration of gadolinium (Gd)-based contrast agents (GBCAs) in patients who suffer from renal impairment. Meanwhile, nanomaterials meet biosafety concerns because of their long-term retention in the body. Herein, we propose a small-molecule manganese-based imaging probe Mn-PhDTA as an alternative to GBCAs to assess renal insufficiency for the first time. Mn-PhDTA was synthesized via a simple three-step reaction with a total yield of up to 33.6%, and a gram-scale synthesis can be realized. Mn-PhDTA has an r1 relaxivity of 2.72 mM-1 s-1 at 3.0 T and superior kinetic inertness over Gd-DTPA and Mn-EDTA with a dissociation time of 60 min in the presence of excess Zn2+. In vivo and in vitro experiments demonstrate their good stability and biocompatibility. In the unilateral ureteral obstruction rats, Mn-PhDTA provided significant MR signal enhancement, enabled distinguishing structure changes between the normal and damaged kidneys, and evaluated the renal function at different injured stages. Mn-PhDTA could act as a potential MRI contrast agent candidate for the replacement of GBCAs in the early detection of kidney dysfunction and analysis of kidney disease progression.

The Spectrum of Biopsy-Proven Kidney Diseases, Causes, and Renal Outcomes in Acute Kidney Injury Patients

INTRODUCTION

Acute kidney injury (AKI) is a group of highly heterogeneous, complicated clinical syndromes. Although kidney biopsy plays an irreplaceable role in evaluating complex AKI, a few studies have focused on the clinicopathology of AKI biopsies. This study analyzed the pathological disease spectrum, causes, and renal outcomes of biopsied AKI patients.

METHODS

We retrospectively included 2,027 AKI patients who underwent kidney biopsies at a national clinical research center of kidney diseases from 2013 through 2018. To compare the biopsied AKI cases without and with coexisting glomerulopathy, patients were classified into acute tubular/tubulointerstitial nephropathy-associated AKI (ATIN-AKI) and glomerular disease-associated AKI (GD-AKI) groups.

RESULTS

Of 2,027 biopsied AKI patients, 65.1% were male, with a median age of 43 years. A total of 1,590 (78.4%) patients had coexisting GD, while only 437 (21.6%) patients had ATIN alone. The AKI patients with GD mainly (53.5%) manifested as stage 1 AKI, while most ATIN-AKI patients (74.8%) had stage 3 AKI. In the ATIN-AKI group, 256 (58.6%) patients had acute interstitial nephritis (AIN), and 77 (17.6%) had acute tubular injury (ATI). ATIN-AKI was mainly caused by drugs in 85.5% of AIN and 63.6% of ATI cases, respectively. In AKI patients with coexisting GD, the leading pathological diagnoses in over 80% of patients were IgA nephropathy (IgAN, 22.5%), minimal change disease (MCD, 17.5%), focal segmental glomerulosclerosis (FSGS, 15.3%), lupus nephritis (LN, 11.9%), membranous nephropathy (MN, 10.2%), and ANCA-associated vasculitis (AAV, 4.7%). A total of 775 patients were followed up within 3 months after renal biopsy; ATIN-AKI patients achieved statistically higher complete renal recovery than the GD-AKI patients (83.5% vs. 70.5%, p < 0.001).

CONCLUSIONS

Most biopsied AKI patients have coexisting GD, while ATIN alone is seen less frequently. ATIN-AKI is mainly caused by drugs. In GD-AKI patients, IgAN, MCD, FSGS, LN, MN, and AAV are the leading diagnoses. Compared to AKI patients without GD, patients with GD suffer from worse renal function recovery.

Risk of bleeding after percutaneous native kidney biopsy in patients receiving low-dose aspirin: a single-center retrospective study

BACKGROUND

Although discontinuation of antiplatelet agents at least 5 days before kidney biopsy is commonly recommended, the evidence behind this practice is of low level. Indeed, few non-randomized studies previously showed an equivalent risk of bleeding in patients receiving aspirin therapy.

METHODS

We conducted a single center retrospective study comparing the risk of complications after percutaneous native kidney biopsy in patients who received low-dose aspirin (ASA) within 5 days from biopsy and those who did not. The main outcome was the difference in the incidence of major complications (red blood cell transfusion, need for selective arterial embolization, surgery, nephrectomy). Secondary outcomes included difference in minor complications, comparison between patients who received ASA within 48 h or within 3-5 days, identification of independent factors predictive of major complications.

RESULTS

We analyzed data on 750 patients, of whom 94 received ASA within 5 days from biopsy. There were no significant differences in the proportion of major complications in patients receiving or not receiving ASA (2.59% and 3.19%, respectively, percentage point difference 1%, 95% CI - 3 to 4%, p = 0.74). Groups were also comparable for minor complications; among patients receiving ASA, there were no differences in major bleeding between those who received ASA within 48 h or 3-5 days from biopsy. Significant baseline predictors of major bleeding in our cohort were platelet count lower than 120*10³/microliter, higher diastolic blood pressure and higher blood urea.

CONCLUSIONS

Treatment with low-dose ASA within 5 days from kidney biopsy did not increase the risk of complications after the procedure.

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.

Soluble and cell-based markers of immune checkpoint inhibitor-associated nephritis

BACKGROUND

Non-invasive biomarkers of immune checkpoint inhibitor-associated acute tubulointerstitial nephritis (ICI-nephritis) are urgently needed. Because ICIs block immune checkpoint pathways that include cytotoxic T lymphocyte antigen 4 (CTLA4), we hypothesized that biomarkers of immune dysregulationpreviously defined in patients with congenital CTLA4 deficiency, including elevated soluble interleukin-2 receptor alpha (sIL-2R) and flow cytometric cell-based markers of B and T cell dysregulation in peripheral blood may aid the diagnosis of ICI-nephritis.

METHODS

A retrospective cohort of patients diagnosed with ICI-nephritis was compared with three prospectively enrolled control cohorts: ICI-treated controls without immune-related adverse events, patients not on ICIs with hemodynamic acute kidney injury (hemodynamic AKI), and patients not on ICIs with biopsy proven acute interstitial nephritis from other causes (non-ICI-nephritis). sIL-2R level and flow cytometric parameters were compared between groups using Wilcoxon rank sum test or Kruskal-Wallis test. Receiver operating characteristic curves were generated to define the accuracy of sIL-2R and flow cytometric biomarkers in diagnosing ICI-nephritis. The downstream impact of T cell activation in the affected kidney was investigated using archived biopsy samples to evaluate the gene expression of IL2RA, IL-2 signaling, and T cell receptor signaling in patients with ICI-nephritis compared with other causes of drug-induced nephritis, acute tubular injury, and histologically normal controls.

RESULTS

sIL-2R level in peripheral blood was significantly higher in patients with ICI-nephritis (N=24) (median 2.5-fold upper limit of normal (ULN), IQR 1.9-3.3), compared with ICI-treated controls (N=10) (median 0.8-fold ULN, IQR 0.5-0.9, p<0.001) and hemodynamic AKI controls (N=6) (median 0.9-fold-ULN, IQR 0.7-1.1, p=0.008). A sIL-2R cut-off point of 1.75-fold ULN was highly diagnostic of ICI-nephritis (area under the curve >96%) when compared with either ICI-treated or hemodynamic AKI controls. By peripheral blood flow cytometry analysis, lower absolute CD8+T cells, CD45RA+CD8+ T cells, memory CD27+B cells, and expansion of plasmablasts were prominent features of ICI-nephritis compared with ICI-treated controls. Gene expressions for IL2RA, IL-2 signaling, and T cell receptor signaling in the kidney tissue with ICI-nephritis were significantly higher compared with controls.

CONCLUSION

Elevated sIL-2R level and flow cytometric markers of both B and T cell dysregulation may aid the diagnosis of ICI-nephritis.

Development and external validation of a diagnostic model for biopsy-proven acute interstitial nephritis using electronic health record data

BACKGROUND

Patients with acute interstitial nephritis (AIN) can present without typical clinical features, leading to a delay in diagnosis and treatment. We therefore developed and validated a diagnostic model to identify patients at risk of AIN using variables from the electronic health record.

METHODS

In patients who underwent a kidney biopsy at Yale University between 2013 and 2018, we tested the association of &gt;150 variables with AIN, including demographics, comorbidities, vital signs and laboratory tests (training set 70%). We used least absolute shrinkage and selection operator methodology to select prebiopsy features associated with AIN. We performed area under the receiver operating characteristics curve (AUC) analysis with internal (held-out test set 30%) and external validation (Biopsy Biobank Cohort of Indiana). We tested the change in model performance after the addition of urine biomarkers in the Yale AIN study.

RESULTS

We included 393 patients (AIN 22%) in the training set, 158 patients (AIN 27%) in the test set, 1118 patients (AIN 11%) in the validation set and 265 patients (AIN 11%) in the Yale AIN study. Variables in the selected model included serum creatinine {adjusted odds ratio [aOR] 2.31 [95% confidence interval (CI) 1.42-3.76]}, blood urea nitrogen:creatinine ratio [aOR 0.40 (95% CI 0.20-0.78)] and urine dipstick specific gravity [aOR 0.95 (95% CI 0.91-0.99)] and protein [aOR 0.39 (95% CI 0.23-0.68)]. This model showed an AUC of 0.73 (95% CI 0.64-0.81) in the test set, which was similar to the AUC in the external validation cohort [0.74 (95% CI 0.69-0.79)]. The AUC improved to 0.84 (95% CI 0.76-0.91) upon the addition of urine interleukin-9 and tumor necrosis factor-α.

CONCLUSIONS

We developed and validated a statistical model that showed a modest AUC for AIN diagnosis, which improved upon the addition of urine biomarkers. Future studies could evaluate this model and biomarkers to identify unrecognized cases of AIN.

Immune checkpoint inhibitors and kidney disease

PURPOSE OF REVIEW

Immune checkpoint inhibitors (ICIs) have changed the landscape of cancer treatment. However, use of ICIs can be limited by inflammatory toxicities referred to as immune-related adverse events (irAEs). ICI-associated acute kidney injury (ICI-associated AKI) affects 3-5% of ICI users.

RECENT FINDINGS

With the rapidly growing indication of ICI, knowledge of ICI-associated kidney toxicity has also expanded from case series to large multicentre cohort studies. In this review, we discuss the clinical features, risk factors, clinicopathological correlations and prognosis of ICI-associated AKI from the most recent rigorously conducted retrospective cohort studies. We also discuss recent advances in diagnostic biomarker investigation, treatment and the unique challenge faced in the kidney transplant population.

SUMMARY

With more comprehensive understanding of the clinical features and risk factors, ICI-associated AKI is commonly diagnosed clinically, especially given the inherent challenges performing a kidney biopsy in the cancer population; however, this highlights the urgent need for improved noninvasive diagnostic biomarkers to aid diagnosis and prognosis. Prospective studies are needed to better define the optimal treatment of ICI-associated AKI and to minimize the risk of graft loss in patients with kidney transplant who require ICIs.

Urine Uromodulin as a Biomarker of Kidney Tubulointerstitial Fibrosis

BACKGROUND AND OBJECTIVES

Uromodulin, produced exclusively in the kidney's thick ascending limb, is a biomarker of kidney tubular health. However, the relationship between urine uromodulin and histologic changes in the kidney tubulointerstitium has not been characterized. In this study, we test the association of urine uromodulin with kidney histologic findings in humans and mice.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We investigated the independent association of urine uromodulin measured at the time of kidney biopsy with histologic features in 364 participants at two academic medical centers from 2015 to 2018 using multivariable linear regression models. This relationship was further examined by comparison of uromodulin staining in murine models of kidney fibrosis and repair.

RESULTS

We found urine uromodulin to be correlated with serum creatinine (rho=-0.43; P<0.001), bicarbonate (0.20; P<0.001), and hemoglobin (0.11; P=0.03) at the time of biopsy but not with urine albumin (-0.07; P=0.34). Multivariable models controlling for prebiopsy GFR, serum creatinine at biopsy, and urine albumin showed higher uromodulin to be associated with lower severity of interstitial fibrosis/tubular atrophy and glomerulosclerosis (interstitial fibrosis/tubular atrophy: -3.5% [95% confidence intervals, -5.7% to -1.2%] and glomerulosclerosis: -3.3% [95% confidence intervals, -5.9% to -0.6%] per two-fold difference in uromodulin). However, when both interstitial fibrosis/tubular atrophy and glomerulosclerosis were included in multivariable analysis, only interstitial fibrosis/tubular atrophy was independently associated with uromodulin (interstitial fibrosis/tubular atrophy: -2.5% [95% confidence intervals, -4.6% to -0.4%] and glomerulosclerosis: -0.9% [95% confidence intervals, -3.4% to 1.5%] per two-fold difference in uromodulin). In mouse kidneys, uromodulin staining was found to be lower in the fibrotic model than in normal or repaired models.

CONCLUSIONS

Higher urine uromodulin is independently associated with lower tubulointerstitial fibrosis in both human kidney biopsies and a mouse model of fibrosis.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2022_08_10_CJN04360422.mp3.

Urine testing to differentiate glomerular from tubulointerstitial diseases on kidney biopsy

Background

Differentiating between glomerular and tubulointerstitial diseases can guide selection of appropriate patients for kidney biopsy. The aim of this study is to identify urine tests that can differentiate between these histological diagnoses.

Methods

In this sub-study of a prospectively enrolled cohort of participants with urine samples concurrent with their kidney biopsy, we tested the association of 24 features on urinalysis, urine sediment microscopy, and biomarkers of glomerular and tubular injury and inflammation with histological diagnosis of glomerular or tubulointerstitial disease. We selected a combination of features associated with glomerular disease using stepwise forward and backward regression, and LASSO algorithm after dividing the cohort into training (70%) and test (30%) sets.

Results

Of 359 participants, 121 had glomerular, 89 had tubulointerstitial diseases, and 149 were classified as mixed. Compared to patients with tubulointerstitial diseases, those with glomerular diseases had more dipstick hematuria (3+ vs. 1+, P < 0.001) and urine albumin (1.25 vs. 0.09 mg/mg, P < 0.001). Patients with glomerular diseases had higher levels of tubular health biomarkers (Uromodulin, 1.22 vs. 0.92, P = 0.03). In a multivariable model, higher urine albumin, dipstick blood, and urine uromodulin were independently associated with higher odds of glomerular diseases (test set AUC, 0.81 (0.69, 0.93)).

Conclusion

Urine tests, including urine albumin, dipstick blood, and urine uromodulin, were associated with the histological diagnosis of glomerular disease. These findings can help clinicians differentiate between glomerular and tubulointerstitial diseases and guide clinical decisions regarding a kidney biopsy.

Mortality after acute kidney injury and acute interstitial nephritis in patients prescribed immune checkpoint inhibitor therapy

BACKGROUND

In patients receiving immune checkpoint inhibitor (ICI) therapy, acute kidney injury (AKI) is common, and can occur either from kidney injury unrelated to ICI use or from immune activation resulting in acute interstitial nephritis (AIN). In this study, we test the hypothesis that occurrence of AIN indicates a favorable treatment response to ICI therapy and therefore among patients who develop AKI while on ICI therapy, those with AIN will demonstrate greater survival compared with others with AKI.

METHODS

In this observational cohort study, we included participants initiated on ICI therapy between 2013 and 2019. We tested the independent association of AKI and estimated AIN (eAIN) with mortality up to 1 year after therapy initiation as compared with those without AKI using time-varying Cox proportional hazard models controlling for demographics, comorbidities, cancer type, stage, and therapy, and baseline laboratory values. We defined eAIN as those with a predicted probability of AIN >90th percentile derived from a recently validated diagnostic model.

RESULTS

Of 2207 patients initiated on ICIs, 617 (28%) died at 1 year and 549 (25%) developed AKI. AKI was independently associated with higher mortality (adjusted HR, 2.28 (95% CI 1.90 to 2.72)). Those AKI patients with eAIN had more severe AKI as reflected by a higher peak serum creatinine (3.3 (IQR 2.1-6.1) vs 1.4 (1.2-1.9) mg/dL, p<0.001) but exhibited lower mortality than those without eAIN in univariable analysis (HR 0.43 (95% CI 0.21 to 0.89)) and after adjusting for demographics, comorbidities, and cancer type and severity (adjusted HR 0.44 (95% CI 0.21 to 0.93)).

CONCLUSION

In patients treated with ICI, mortality was higher in those with AKI unrelated to ICI but lower in those where the underlying etiology was AIN. Future studies could evaluate the association of biopsy-proven or biomarker-proven AIN with mortality in those receiving ICI therapy.

Acute Brachial Arterial Embolic Occlusion Following Anticoagulant Discontinuation in a Renal Biopsy of a Nephrotic Syndrome Patient

A 73-year-old woman with atrial fibrillation treated with rivaroxaban was hospitalized for nephrotic syndrome. After discontinuation of rivaroxaban to lower the risk of hemorrhagic events, a renal biopsy was performed. Rivaroxaban was scheduled to resume a week after the biopsy to prevent renal hemorrhaging. However, she developed acute brachial arterial embolic occlusion and mural thrombosis in the abdominal aorta before resuming rivaroxaban. If immune-mediated renal diseases are suspected in anticoagulated patients at a risk of thrombotic events, physicians should consider initiating glucocorticoid therapy without a renal biopsy in order to avoid hemorrhagic and thrombotic events.

Safety of Renal Biopsy by Physicians with Short Nephrology Experience

Percutaneous renal biopsy is an essential tool for diagnosing various renal diseases; however, little is known about whether renal biopsy performed by physicians with short nephrology experience is safe in Japan. This study included 238 patients who underwent percutaneous renal biopsy between April 2017 and September 2020. We retrospectively analyzed the frequency of post-renal biopsy complications (hemoglobin decrease of ≥10%, hypotension, blood transfusion, renal artery embolization, nephrectomy and death) and compared their incidence among physicians with varied experience in nephrology. After renal biopsy, a hemoglobin decrease of ≥10%, hypotension and transfusion occurred in 13.1%, 3.8% and 0.8% of patients, respectively. There were no cases of post-biopsy renal artery embolism, nephrectomy, or death. The composite complication rate was 16.0%. The incidence of post-biopsy complications was similar between physicians with ≥3 years and <3 years of clinical nephrology experience (12.5% vs. 16.8%, p = 0.64). Furthermore, the post-biopsy composite complication rates were similar between physicians with ≥6 months and <6 months of clinical nephrology experience (16.3% vs. 15.6%, p > 0.99). Under attending nephrologist supervision, a physician with short clinical nephrology experience can safely perform renal biopsy.

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.

A Color Flow Tract in Ultrasound-Guided Random Renal Core Biopsy Predicts Complications

OBJECTIVES

To determine patient and procedural risk factors for major complications in ultrasound (US)-guided random renal core biopsy.

METHODS

Random renal biopsies performed by radiologists in the US department at a single institution between 2014 and 2018 were retrospectively reviewed. The patient's age, sex, race, and estimated glomerular filtration rate (eGFR) were recorded. The biopsy approach, needle gauge, length of cores, number of throws, and presence of a color flow tract were recorded. Outcome data included minor and major complications. Associations between variables were tested with χ² analyses and univariable/multivariable logistic regression models.

RESULTS

A total of 231 biopsies (167 native and 64 allografts) were reviewed. There was no significant difference in the sex, age, race, or eGFR between native and allograft groups. The overall rate for any complication was 18.2%, with a 4.3% rate of major complications, which was significantly greater in native compared to allograft biopsies (6% versus 0%; P = .045). A risk analysis in native biopsies only showed that major complications were significantly associated with a low eGFR such that patients with stage 4 or 5 kidney disease had higher odds of complications (odds ratio [95% confidence interval]: stage 4, 9.405 [1.995-44.338]; P = .0393; stage 5, 10.749 [2.218-52.080]; P = .0203) than patients with normal function (eGFR >60 mL/min). The presence of a color flow tract portended a 10.7 times greater risk of having any complication (95% confidence interval, 4.595-24.994; P < .001). Other procedural factors were not significantly associated with complications.

CONCLUSIONS

There is an increased risk of major complications in US-guided random native kidney biopsy in patients with a low eGFR (<30 mL/min) and a patent color flow tract in the immediate postbiopsy setting.

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.

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.

Inflammatory leucocyte infiltrates are associated with recovery in biopsy-proven acute interstitial nephritis: a 20-year registry-based case series

Background

Acute interstitial nephritis (AIN) is a renal injury causing renal function deterioration and requiring renal replacement therapy (RRT) in a substantial number of cases. Therapy is based on withdrawal of suspicious causative drugs or the underlying diseases and/or steroid application if renal function is not restored after cessation of the underlying condition. Hard clinical evidence for augmenting steroid therapy is not available.

Methods

We reviewed the course and diagnosis for >20 years among all 1126 biopsied samples of our tertiary renal centre.

Results

49 (4.4%) were diagnosed with primary AIN, corresponding to an annual incidence of 1/100 000 population; 17 out of 49 biopsy-proven AIN patients required short-term or long-term (n = 5) RRT. According to a combined outcome criterion of coming off dialysis and/or reaching serum creatinine <200 µmol/L, 19 patients reached recovery whereas 20 did not. Among 39 patients with a comprehensive clinical and histopathological data set, presence of cortical scars, AIN histological activity (acute leucocyte infiltrates) and proteinuria were baseline parameters discriminating significantly between groups with or without recovery. No associations with the presence of specific drugs were found. Therapeutic use of steroids was associated with a lower probability of recovery (P = 0.008), presumably due to inclusion bias.

Conclusions

Following our basic finding of the importance of histopathological parameters of acuity associated with recovery, we argue for the inauguration of grading measures to characterize this issue quantitatively and make it usable for future controlled investigations. Finally, we provide a suggestion for a therapeutic algorithm in the management of AIN.

Percutaneous Kidney Biopsy and the Utilization of Blood Transfusion and Renal Angiography Among Hospitalized Adults

Introduction

Data on percutaneous kidney biopsy (KBx) incidence and frequencies of hemorrhagic complications among inpatients are limited.

Methods

Using nationally representative US hospitalization discharge data, we report temporal trends in inpatient KBx rates from 2007 to 2014 and estimate frequencies of, and risk factors for, utilization of packed red blood cell (pRBC) transfusion and renal angiography.

Results

From 2007 to 2014, rates of native KBx among adult inpatients increased from 8.2 to 10.0 per 100,000, while transplant KBx rates declined from 3.6 to 3.1 per 100,000. We studied 35,183 and 14,266 discharge records with native and transplant KBx. We found that 5.7% (95% confidence interval [CI]: 5.3%–6.0%) of inpatients undergoing native KBx and 4.9% (4.2%–5.5%) of those undergoing transplant KBx received a pRBC transfusion within 2 days of biopsy. Similarly, 0.6% (0.5%–0.7%) of inpatients undergoing native KBx and 0.4% (0.2%–0.5%) undergoing transplant KBx received a renal angiogram within 2 days of KBx. For inpatient native KBx, female sex, older age, higher chronic kidney disease stage, acute renal failure, lupus, vasculitis, cirrhosis, multiple myeloma/paraproteinemia, and anemia of chronic disease were independently associated with increased odds of pRBC transfusion; cirrhosis and end-stage renal disease (ESRD) were associated with increased odds, and nephrotic syndrome was associated with decreased odds, of renal angiography.

Conclusions

In this large population-based study of inpatient KBx practices, we demonstrate increasing rates of inpatient native KBx among US adults and provide accurate estimates of the frequencies of, and risk factors for, pRBC transfusion and renal angiography following inpatient KBx.

Complications of Percutaneous Renal Biopsy

Percutaneous renal biopsy is widely used for diagnosis, prognosis, and management of nephropathies. Complications may arise after renal biopsy, most commonly in the form of bleeding. Efforts should be taken to optimize modifiable risk factors such as hypertension, thrombocytopenia, and coagulopathy prior to the procedure. Unmodifiable risk factors such as poor renal function, gender, and underlying histologic diagnosis may be used to identify high-risk patients. Delayed presentation of bleeding complications is common, and close clinical follow-up is crucial.

Urine TNF-α and IL-9 for clinical diagnosis of acute interstitial nephritis

BACKGROUNDClinical diagnosis of acute interstitial nephritis (AIN) is challenging because of lack of a diagnostic biomarker and requires a kidney biopsy. We hypothesized that AIN is mediated by specific T cell subsets such that specific T cell cytokine levels could serve as biomarkers to distinguish AIN from other causes of acute kidney disease (AKD).METHODSWe enrolled consecutive sampling participants who underwent a kidney biopsy for AKD evaluation at 2 centers between 2015 and 2018. Three pathologists independently established AIN diagnosis through review of kidney biopsies. Through univariable and multivariable analysis of 12 selected urine and plasma cytokines, we identified 2 that were diagnostic of AIN.RESULTSOf the 218 participants, 32 (15%) were diagnosed with AIN by all 3 pathologists. Participants with AIN had consistently higher levels of urine TNF-α and IL-9 than those with other diagnoses, including acute tubular injury, glomerular diseases, and diabetic kidney disease, and those without any kidney disease. As compared with participants in the lowest quartile, we noted higher odds of AIN in participants in the highest quartiles of TNF-α levels (adjusted odds ratio, 10.9 [1.8, 65.9]) and IL-9 levels (7.5 [1.2, 45.7]) when controlling for blood eosinophils, leukocyturia, and proteinuria. Addition of biomarkers improved area under receiver operating characteristic curve over clinicians' prebiopsy diagnosis (0.84 [0.78, 0.91]) vs. 0.62 [(0.53, 0.71]) and a model of current tests (0.84 [0.76, 0.91] vs. 0.69 [0.58, 0.80]).CONCLUSIONSInclusion of urinary TNF-α and IL-9 improves discrimination over clinicians' prebiopsy diagnosis and currently available tests for AIN diagnosis.FUNDINGSupported by NIH awards K23DK117065, T32DK007276, K24DK090203, K23DK097201, R01DK113191, UG3-DK114866, P30DK079310; the Robert E. Leet and Clara Guthrie Patterson Trust; and American Heart Association award 18CDA34060118.

Renal biopsy: it is time for pragmatism and consensus

To obtain truly informed consent, we must be able to advise our patients accurately about the relative risk and benefit of any treatment plan. Percutaneous renal biopsy remains the gold standard investigation in the evaluation of intrinsic renal disease. There have been significant improvements in practice over the past decades with regards to percutaneous renal biopsy. Across centres, we appear now to have reached agreement on many aspects of this procedure, such as the need for blood pressure control, avoidance of coagulopathy, use of spring-loaded needles under direct imaging guidance and a need to monitor for complications. The authors from Rush University Medical Centre provide reassurance that renal biopsy in the modern era remains a safe procedure with a low rate of significant bleeding. There remain areas of divergence in practice that may have unintended and deleterious consequences: administration of desmopressin and discontinuation of aspirin, for example, both carry a risk of thrombosis. It is our opinion that it is time to reach consensus on our interpretation of the available data and to draw up guidelines to standardize our biopsy practice internationally.