Prognostic value of tubular proteinuria and enzymuria in nonoliguric acute tubular necrosis

Drug induced nephrotoxicity- A mechanistic approach

The main goal of the treatment of patients is its effectiveness and safety. However, all currently prescribed drugs being used also have certain adverse effects, which might be seen as an unavoidable but necessary cost of pharmacotherapy. The kidney is the primary organ for xenobiotics elimination, making it particularly susceptible to the harmful effects of drugs and their metabolites during their excretion from the body. Moreover, certain medications have a preferential nephrotoxicity potential, which means that using them increases the risk of kidney injury. Drug nephrotoxicity is, therefore, both a significant problem and a complication of pharmacotherapy. It should be noted that, there is presently no accepted definition of drug-induced nephrotoxicity and no established diagnostic criteria. The current review briefly describes the pathogenic mechanism of drug-induced nephrotoxicity, the various basic drugs with nephrotoxicity potential and the renal biomarkers for the treatment of the drug-related kidney damage.

Revisiting the Role of NAG across the Continuum of Kidney Disease

Acute and chronic kidney diseases are an evolving continuum for which reliable biomarkers of early disease are lacking. The potential use of glycosidases, enzymes involved in carbohydrate metabolism, in kidney disease detection has been under investigation since the 1960s. N-acetyl-beta-D-glucosaminidase (NAG) is a glycosidase commonly found in proximal tubule epithelial cells (PTECs). Due to its large molecular weight, plasma-soluble NAG cannot pass the glomerular filtration barrier; thus, increased urinary concentration of NAG (uNAG) may suggest injury to the proximal tubule. As the PTECs are the workhorses of the kidney that perform much of the filtration and reabsorption, they are a common starting point in acute and chronic kidney disease. NAG has previously been researched, and it is widely used as a valuable biomarker in both acute and chronic kidney disease, as well as in patients suffering from diabetes mellitus, heart failure, and other chronic diseases leading to kidney failure. Here, we present an overview of the research pertaining to uNAG’s biomarker potential across the spectrum of kidney disease, with an additional emphasis on environmental nephrotoxic substance exposure. In spite of a large body of evidence strongly suggesting connections between uNAG levels and multiple kidney pathologies, focused clinical validation tests and knowledge on underlining molecular mechanisms are largely lacking.

Pathophysiology of Acute Kidney Injury in Critical Illness: A Narrative Review

Acute kidney injury (AKI) is a syndrome that entails a rapid decline in kidney function with or without injury. The consequences of AKI among acutely ill patients are dire and lead to higher mortality, morbidity, and healthcare cost. To prevent AKI and its short and long-term repercussions, understanding its pathophysiology is essential. Depending on the baseline kidney histology and function reserves, the number of kidney insults, and the intensity of each insult, the clinical presentation of AKI may differ. While many factors are capable of inducing renal injury, they can be categorized into a few processes. The three primary processes reported in the literature are hemodynamic changes, inflammatory reactions, and nephrotoxicity. The majority of patients with AKI will suffer from more than one during their development and/or progression of AKI. Moreover, the development of one usually leads to the instigation of another. Thus, the interactions and progression between these mechanisms may determine the severity and duration of the AKI. Other factors such as organ crosstalk and how our concurrent therapies interact with these mechanisms complicate the pathophysiology of the progression of the AKI even further. In this narrative review article, we describe these three main pathophysiological processes that lead to the development and progression of AKI. © 2022 American Physiological Society. Compr Physiol 12: 1-14, 2022.

Assessment of urine sample quality by the simultaneous measurement of urinary γ-glutamyltransferase and lactate dehydrogenase enzyme activities: possible application to unravel cheating in drugs of abuse testing

OBJECTIVES

Evaluation of the simultaneous measurement of urinary γ-glutamyltransferase (γGT) and lactate dehydrogenase (LDH) to discriminate fresh from previously frozen specimens in urine drug monitoring.

METHODS

Two widely available photometric tests (Siemens Healthineers Atellica) were used to determine the range of urinary γGT and LDH excretion and to study the decay in urinary enzyme activity under various storage conditions (room temperature, 4-8 °C, -18 °C, -80 °C). From these data, cut-off values were established and evaluated in split (fresh/frozen) specimens.

RESULTS

Both assays allow robust, reliable, and simultaneous determination of urinary γGT and LDH. In healthy subjects, the 95% reference intervals for enzyme activity in native urine were γGT: 24.4-100.4 U/g Crea (creatinine) and LDH: 2.5-45.8 U/g Crea. Frozen storage for at least 7 days at -18 °C resulted in a loss of activity to less than 50% in both enzymes. Cut-offs for frozen samples were γGT≤33.2 U/g Crea and LDH≤ 8.4 U/g Crea. When applied to 100 sample pairs (fresh/frozen), 86.5% (173/200) of the measurements were conclusive and the combination of concordant enzyme measurements (low γGT/low LDH or high γGT/high LDH) was able to predict the mode of storage with a sensitivity of 96.3% and a specificity of 96.7%.

CONCLUSIONS

The additional measurements of urinary γGT and LDH can be used to detect previously frozen urine specimens. A simple protocol is proposed to provide additional information on sample quality when deceit is suspected. The procedure can be easily integrated into the standard workflow of urinary drug monitoring.

Improving acute kidney injury diagnostic precision using biomarkers

Acute kidney injury (AKI) is common in hospitalized patients of all ages and is associated with significant morbidity and mortality. Accurate prediction and early identification of AKI is of utmost importance because no therapy exists to mitigate AKI once it has occurred. Yet, serum creatinine lacks adequate sensitivity and specificity, and quantification of urine output is challenging in incontinent children without indwelling bladder catheters. Integration of clinically available biomarkers have the potential to delineate unique AKI phenotypes that could have important prognostic and therapeutic implications. Plasma Cystatin C, urine neutrophil gelatinase associated lipocalin (NGAL) and the urinary product of tissue inhibitor metalloproteinase (TIMP-2) and insulin growth factor binding protein-7 (IGFBP7) are clinically available. These biomarkers have been studied in heterogenous populations across the age spectrum and in a variety of clinical settings for prediction of AKI. The purpose of this review is to describe and discuss the clinically available AKI biomarkers including how they have been used to delineate AKI phenotypes.

Urinary concentrations of neonicotinoid insecticides were related to renal tubular dysfunction and neuropsychological complaints in Dry-zone of Sri Lanka

Neonicotinoids are systemic insecticides used since the 1990’s , that possess renal tubular toxicity. We conducted a field-based descriptive study in the North Central Dry-zone of Sri Lanka, where chronic kidney disease (CKD) of unknown etiology has been increasing since the 1990’s. To elucidate the relationship between renal tubular dysfunctions and urinary neonicotinoids concentrations, we collected spot urine samples from15 CKD patients, 15 family members, and 62 neighbors in 2015, analyzed two renal tubular biomarkers, Cystatin-C and L-FABP, quantified seven neonicotinoids and a metabolite N-desmethyl-acetamiprid by LC–MS/MS; and we investigated their symptoms using a questionnaire. Cystatin-C and L-FABP had a positive correlation (p < 0.001). N-Desmethyl-acetamiprid was detected in 92.4% of the urine samples, followed by dinotefuran (17.4%), thiamethoxam (17.4%), clothianidin (9.8%), thiacloprid and imidacloprid. Dinotefuran and thiacloprid have never been registered in Sri Lanka. In High Cystatin-C group (> 70 μg/gCre, n = 7), higher urinary concentration of dinotefuran (p = 0.009), and in Zero Cystatin-C group (< LOQ, n = 7), higher N-desmethyl-acetamiprid (p = 0.013), dinotefuran (p = 0.049), and thiacloprid (p = 0.035), and more complaints of chest pains, stomachache, skin eruption and diarrhea (p < 0.05) were found than in Normal Cystatin-C group (n = 78). Urinary neonicotinoids may be one of the potential risk factors for renal tubular dysfunction in this area.

A randomised controlled trial of succinylated gelatin (4%) fluid on urinary acute kidney injury biomarkers in cardiac surgical patients

Background

Fluid resuscitation is frequently required for cardiac surgical patients admitted to the intensive care unit. The ideal fluid of choice in regard to efficacy and safety remains uncertain. Compared with crystalloid fluid, colloid fluid may result in less positive fluid balance. However, some synthetic colloids are associated with increased risk of acute kidney injury (AKI). This study compared the effects of succinylated gelatin (4%) (GEL) with compound sodium lactate (CSL) on urinary AKI biomarkers in patients after cardiac surgery.

Methods

Cardiac surgical patients who required an intravenous fluid bolus of at least 500 mL postoperatively were randomly allocated to receive GEL or CSL as the resuscitation fluid of choice for the subsequent 24 h. Primary outcomes were serial urinary neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C concentrations measured at baseline, 1 h, 5 h and 24 h after enrolment, with higher concentrations indicating greater kidney injury. Secondary biomarker outcomes included urinary clusterin, α1-microglobulin and F₂-isoprostanes concentrations. Differences in change of biomarker concentration between the two groups over time were compared with mixed-effects regression models. Statistical significance was set at P < 0.05.

Results

Forty cardiac surgical patients (n = 20 per group) with similar baseline characteristics were included. There was no significant difference in the median volume of fluid boluses administered over 24 h between the GEL (1250 mL, Q1–Q3 500–1750) and CSL group (1000 mL, Q1–Q3 500–1375) (P = 0.42). There was a significantly greater increase in urinary cystatin C (P < 0.001), clusterin (P < 0.001), α1-microglobulin (P < 0.001) and F₂-isoprostanes (P = 0.020) concentrations over time in the GEL group, compared to the CSL group. Change in urinary NGAL concentration (P = 0.68) over time was not significantly different between the groups. The results were not modified by adjustment for either urinary osmolality or EuroSCORE II predicted risk of mortality.

Conclusions

This preliminary randomised controlled trial showed that use of succinylated gelatin (4%) for fluid resuscitation after cardiac surgery was associated with increased biomarker concentrations of renal tubular injury and dysfunction, compared to crystalloid fluid. These results generate concern that use of intravenous gelatin fluid may contribute to clinically relevant postoperative AKI.

Trial registration ANZCTR.org.au, ACTRN12617001461381. Registered on 16th October, 2017, http://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=373619&isReview=true.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-021-00412-9.

Biomarkers in Acute Kidney Injury

Biomarkers have become a pillar of precision medicine in acute kidney injury (AKI). Traditional markers for diagnosis of AKI are insensitive and insufficient to provide comprehensive information for prognostication. Several emerging biomarkers have shown promising results in large-scale clinical studies. These novel markers likely will be beneficial for personalized AKI prevention and treatment.

Evaluation of Serum and Urine Neutrophil Gelatinase-associated Lipocalin and Cystatin C as Biomarkers of Acute Kidney Injury in Horses

Introduction

Diagnosis of acute kidney injury (AKI) in horses is difficult at the subclinical stage, due to nonspecific clinical signs. The aim of this study was to evaluate the concentrations of selected serum and urinary biomarkers in healthy horses, horses at risk of AKI, and those with clinical AKI.

Material and Methods

Thirty healthy horses, 30 horses at risk of AKI and 11 horses with clinical AKI and azotaemia were included in the study. Serum and urinary neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C were measured using commercially available enzyme immunoassay tests.

Results

The median and (in parentheses) first and third quartile concentrations of selected biomarkers in healthy horses, horses at risk of AKI and horses with AKI were respectively as follows: serum cystatin C – 0.25 (0.19–0.37), 0.23 (0.15–0.37) and 0.61 (0.37–1.13) mg/L; serum NGAL – 50.5 (38.8–58.8), 51.1 (40.4–66.9) and 98.1 (59.4–128.2) ng/mL; urinary NGAL – 20.7 (17.9–24.5), 32.3 (32.7–55.8) and 36.6 (26.8–89.9) ng/mL; and urinary cystatin C – 0.1 (0.07–0.13), 0.13 (0.1–0.2) and 0.34 (0.22–0.37) mg/L. There were significant differences in the concentration of all biomarkers between the healthy and AKI-affected horses.

Conclusion

Horses with AKI all had biomarker concentrations higher than the healthy horses. None of the biomarkers made azotaemia recognisable in all affected horses. The obtained results indicate the need to create a serum and urinary biomarker panel to detect AKI.

Serial serum creatinine, SDMA and urinary acute kidney injury biomarker measurements in dogs envenomated by the European adder (Vipera berus)

Background

Acute kidney injury (AKI) is associated with high morbidity and mortality in dogs, but diagnosis may be impaired due the insensitivity of routine renal function biomarkers to detect earlier or milder forms of injury. Snake envenomation is one of several causes of AKI in dogs and humans. Dogs are commonly envenomated by the European adder (Vipera berus) between April and October each year, but few studies exist examining serial serum creatinine (sCr) and symmetric dimethylarginine (SDMA) measurements and AKI biomarkers in these dogs. Novel urinary biomarkers could improve clinical outcome by allowing earlier diagnosis of and intervention in AKI. The aim of this study was to assess the presence of AKI in dogs envenomated by V. berus at 12, 24 and 36 h after bite, as well as 14 days later, using sCr, SDMA and a panel of urinary AKI biomarkers normalised to urine creatinine (uCr), compared to a group of healthy control dogs.

Results

Thirty-five envenomated dogs and 35 control dogs were included. Serum creatinine did not exceed the upper reference limit at any time point in any dog after envenomation. Serum SDMA did not exceed 0.89 μmol/L in any dog. Compared to controls, urinary albumin/uCr, neutrophil gelatinase-associated lipocalin/uCr and monocyte chemotactic protein-1/uCr were significantly elevated 12 h (P <  0.0001, P <  0.0001, P = 0.01), 24 h (P <  0.001, P <  0.001, P = 0.002) and 36 h (P <  0.001, P <  0.001, P = 0.0008) after bite. Osteopontin/uCr was higher 24 and 36 h after bite (P < 0.0001), kidney injury molecule-1/uCr, interleukin-8/uCr and γ- glutamyl transferase/uCr were significantly higher 36 h after bite (P = 0.003, P = 0.0005, P = 0.001). Urinary cystatin C/uCr was not significantly different to controls at any timepoint. Biomarker/uCr ratios were not significantly different 14 days after envenomation compared to controls.

Conclusion

Urinary biomarker/Cr ratios are indicative of mild transient, non-azotaemic AKI in dogs envenomated by V. berus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-02851-8.

Proteinuria and Clinical Outcomes in Hospitalized COVID-19 Patients: A Retrospective Single-Center Study

BACKGROUND AND OBJECTIVES

Kidney involvement is frequent among patients with coronavirus disease 2019 (COVID-19), and occurrence of AKI is associated with higher mortality in this population. The objective of this study was to describe occurrence and significance of proteinuria in this setting.

DESIGN , SETTING, PARTICIPANTS MEASUREMENTS

We conducted a single-center retrospective study to describe the characteristic features of proteinuria measured within 48 hours following admission among patients with COVID-19 admitted in a tertiary care hospital in France, and to evaluate its association with initiation of dialysis, intensive care unit admission, and death.

RESULTS

Among 200 patients with available data, urine protein-creatinine ratio at admission was ≥1 g/g for 84 (42%), although kidney function was normal in most patients, with a median serum creatinine of 0.94 mg/dl (interquartile range, 0.75-1.21). Median urine albumin-creatinine ratio was 110 mg/g (interquartile range, 50-410), with a urine albumin-protein ratio <50% in 92% of patients. Urine retinol binding protein concentrations, available for 85 patients, were ≥0.03 mg/mmol in 62% of patients. Urine protein-creatinine ratio ≥1 g/g was associated with initiation of dialysis (odds ratio, 4.87; 95% confidence interval, 2.03 to 13.0; P <0.001), admission to the intensive care unit (odds ratio, 3.55; 95% confidence interval, 1.93 to 6.71; P <0.001), and death (odds ratio, 3.56; 95% confidence interval, 1.90 to 6.54; P <0.001).

CONCLUSIONS

Proteinuria is very frequent among patients admitted for COVID-19 and may precede AKI. Low levels of albuminuria suggest a predominant tubular origin, confirmed by the elevated levels of urine retinol binding protein. Urine protein-creatinine ratio ≥1 g/g at admission is strongly associated with poor kidney and patient outcome.

The application of neutrophil gelatin-related lipid delivery protein in evaluation of renal function, nutrition, anemia and inflammation in patients with CKD

OBJECTIVE

To investigate the role of neutrophil gelatinase-associated lipocalin in the evaluation of renal function, nutrition, anemia and inflammation in patients with chronic kidney diseases.

MATERIALS AND METHODS

A total of 302 patients with chronic kidney diseases were selected, and their clinical data, blood neutrophil gelatinase-associated lipocalin levels, renal function, nutrition, anemia, inflammation and calcium, and phosphorus metabolism were analyzed.

RESULT

Serum neutrophil gelatinase-associated lipocalin level increased with the progression of chronic kidney diseases. Higher neutrophil gelatinase-associated lipocalin levels were observed in patients with chronic kidney diseases stage 3b compared with healthy individuals (P<0.05), while the patients with chronic kidney diseases stage 5 showed higher levels compared with other chronic kidney diseases stages (P<0.01). Moreover, the ROC curve showed that neutrophil gelatinase-associated lipocalin had a better diagnostic performance from the chronic kidney diseases stage 3b to 5 (P<0.05). In addition, the serum neutrophil gelatinase-associated lipocalin levels in patient with chronic kidney diseases were negatively correlated with body mass index, number of red blood cells, hemoglobin, transferrin, the estimatedglomerular filtration rate (eGFR), serum calcium (P<0.01); and were positively correlated with mean arterial blood pressure, blood BUN, SCr and alpha 1 microglobulin, beta 2 microglobulin, urinary inhibition C, homocysteine, PTH levels, neutrophils ratio, free serum ferritin and c-reactive protein (P<0.01); while no significant correlation was found with gender, and age (P>0.05).

CONCLUSION

Serum neutrophil gelatinase-associated lipocalin levels are closely related to renal function injury, inflammatory response and anemia-related indicators in patients with chronic kidney diseases, and thus could be used as a diagnostic biomarker for evaluating the degree of renal injury and related complications in patients with chronic kidney diseases.

Detecting acute kidney injury in horses by measuring the concentration of symmetric dimethylarginine in serum

BACKGROUND

Acute kidney injury (AKI) in horses may develop as a complication of a primary disease or following the administration of nephrotoxic drugs, and may pose a diagnostic challenge. Hence, the main objective of this study was to evaluate the concentrations and diagnostic significance of serum symmetric dimethylarginine (SDMA) and conventional renal dysfunction biomarkers in healthy horses, horses at risk of developing AKI, and horses with clinically evident AKI. A second aim was to assess how gastrointestinal disease and exposure to potentially nephrotoxic drugs affected SDMA levels. Thirty healthy horses, 30 horses with gastrointestinal disease and/or receiving phenylbutazone or gentamicin (risk group) and 11 horses with AKI were included in the study. Serum SDMA levels were measured using commercially available enzyme immunoassay tests.

RESULTS

SDMA levels in healthy horses, horses at risk of AKI and horses with AKI were 12 µg/dL (11-14), 12 µg/dL (11-13) and 20 µg/dL (20-37), respectively (all results presented as a median (quartile 1-quartile 3)). There was a significant difference in SDMA concentration between the healthy horses and those with AKI, whereas the SDMA levels in healthy horses and those at risk of AKI were comparable. A SDMA cut-off value of 19 µg/dL was established. Horses from the risk group had higher urine protein concentration and urine protein to creatinine ratio compared with healthy horses. Furthermore, horses with colic from the risk group presented with elevated urine γ-glutamyl transpeptidase to creatinine ratio.

CONCLUSION

The SDMA cut-off value established in healthy horses was higher than previously reported. The SDMA level correlated with the azotaemia levels. Horses from the AKI risk group had normal SDMA levels but single urine parameters was abnormal indicating their higher sensitivity in assessing subclinical kidney dysfunction.

Plasma cystatin C is a marker of renal glomerular injury in children treated with cisplatin or ifosfamide

BACKGROUND

Plasma cystatin C is a potential marker of the glomerular filtration rate (GFR), and urinary cystatin C has been proposed as a marker of tubular dysfunction.

PROCEDURE

A prospective study (NCT02822404) was conducted to assess the benefit of considering cystatin C plasma and urinary levels to better evaluate cisplatin and/or ifosfamide renal toxicity in children with cancer. Plasma ⁵¹ Cr-EDTA clearance as a marker of GFR and urinary markers of tubular toxicity were monitored in 40 children treated by cisplatin and/or ifosfamide. Several equations previously proposed to estimate GFR, with or without inclusion of plasma cystatin C level, were compared. A population pharmacokinetic approach was also used to analyze plasma ⁵¹ Cr-EDTA data, and evaluate the relationship between patient covariates (including plasma cystatin C level) and GFR during the course of chemotherapy treatment.

RESULTS

Equations including plasma cystatin C described GFR changes during chemotherapy better than those without this variable. An equation based on plasma cystatin C, serum creatinine, and body weight enabled us to accurately describe the evolution of GFR during chemotherapy. The urinary cystatin C/creatinine ratio was compared between children with or without tubular toxicity, according to a standard assessment of tubular dysfunction. However, although the urinary cystatin C/creatinine ratio was increased in children with tubular toxicity, this marker does not provide additional information to the well-known markers of tubulopathy.

CONCLUSIONS

Monitoring of plasma cystatin C may be substituted to radionucleide glomerular exploration in children treated by cisplatin and/or ifosfamide.

Biomarker-Guided Risk Assessment for Acute Kidney Injury: Time for Clinical Implementation?

Acute kidney injury (AKI) is a common and serious complication in hospitalized patients, which continues to pose a clinical challenge for treating physicians. The most recent Kidney Disease Improving Global Outcomes practice guidelines for AKI have restated the importance of earliest possible detection of AKI and adjusting treatment accordingly. Since the emergence of initial studies examining the use of neutrophil gelatinase-associated lipocalin (NGAL) and cycle arrest biomarkers, tissue inhibitor metalloproteinase-2 (TIMP-2) and insulin-like growth factor-binding protein (IGFBP7), for early diagnosis of AKI, a vast number of studies have investigated the accuracy and additional clinical benefits of these biomarkers. As proposed by the Acute Dialysis Quality Initiative, new AKI diagnostic criteria should equally utilize glomerular function and tubular injury markers for AKI diagnosis. In addition to refining our capabilities in kidney risk prediction with kidney injury biomarkers, structural disorder phenotypes referred to as "preclinical-" and "subclinical AKI" have been described and are increasingly recognized. Additionally, positive biomarker test findings were found to provide prognostic information regardless of an acute decline in renal function (positive serum creatinine criteria). We summarize and discuss the recent findings focusing on two of the most promising and clinically available kidney injury biomarkers, NGAL and cell cycle arrest markers, in the context of AKI phenotypes. Finally, we draw conclusions regarding the clinical implications for kidney risk prediction.

The Use of Immune Checkpoint Inhibitors in Oncology and the Occurrence of AKI: Where Do We Stand?

Immune checkpoint inhibitors (ICIs) are a novel class of immunotherapy drugs that have improved the treatment of a broad spectrum of cancers as metastatic melanoma, non-small lung cancer or renal cell carcinoma. These humanized monoclonal antibodies target inhibitory receptors (e.g. CTLA-4, PD-1, LAG-3, TIM-3) and ligands (PD-L1) expressed on T lymphocytes, antigen presenting cells and tumor cells and elicit an anti-tumor response by stimulating immune system. Nevertheless, the improved overall survival is complicated by the manifestation of Immune-related Adverse Effects (irAEs). During treatment with ICIs, the most common adverse kidney effect is represented by the development of acute kidney injury (AKI) with the acute tubulointerstitial nephritis as recurrent histological feature. The mechanisms involved in ICIs-induced AKI include the re-activation of effector T cells previously stimulated by nephrotoxic drugs (i.e. by antibiotics), the loss of tolerance versus self-renal antigens, the increased PD-L1 expression by tubular cells or the establishment of a pro-inflammatory milieu with the release of self-reactive antibodies. For renal transplant recipient treated with ICIs, the increased incidence of rejection is a serious concern. Therefore, the combination of ICIs with mTOR inhibitors represents an emerging strategy. Finally, it is relevant to anticipate which patients under ICIs would experience severe irAEs and from a kidney perspective, to predict patients with higher risk of AKI. Here, we provide a detailed overview of ICIs-related nephrotoxicity and the recently described multicenter studies. Several factors have been reported as biomarkers of ICIs-irAEs, in this review we speculate on potential biomarkers for ICIs-associated AKI.

Urinary Biomarkers may Complement the Cleveland Score for Prediction of Adverse Kidney Events After Cardiac Surgery: A Pilot Study

Background

The ability of urinary biomarkers to complement established clinical risk prediction models for postoperative adverse kidney events is unclear. We assessed the effect of urinary biomarkers linked to suspected pathogenesis of cardiac surgery-induced acute kidney injury (AKI) on the performance of the Cleveland Score, a risk assessment model for postoperative adverse kidney events.

Methods

This pilot study included 100 patients who underwent open-heart surgery. We determined improvements to the Cleveland Score when adding urinary biomarkers measured using clinical laboratory platforms (neutrophil gelatinase-associated lipocalin [NGAL], interleukin-6) and those in the preclinical stage (hepcidin-25, midkine, alpha-1 microglobulin), all sampled immediately post-surgery. The primary endpoint was major adverse kidney events (MAKE), and the secondary endpoint was AKI. We performed ROC curve analysis, assessed baseline model performance (odds ratios [OR], 95% CI), and carried out statistical reclassification analyses to assess model improvement.

Results

NGAL (OR [95% CI] per 20 concentration-units wherever applicable): (1.07 [1.01–1.14]), Interleukin-6 (1.51 [1.01–2.26]), midkine (1.01 [1.00–1.02]), 1-hepcidin-25 (1.08 [1.00–1.17]), and NGAL/hepcidin-ratio (2.91 [1.30–6.49]) were independent predictors of MAKE and AKI (1.38 [1.03–1.85], 1.08 [1.01–1.15], 1.01 [1.00–1.02], 1.09 [1.01–1.18], and 3.45 [1.54–7.72]). Category-free net reclassification improvement identified interleukin-6 as a model-improving biomarker for MAKE and NGAL for AKI. However, only NGAL/hepcidin-25 improved model performance for event- and event-free patients for MAKE and AKI.

Conclusions

NGAL and interleukin-6 measured immediately post cardiac surgery may complement the Cleveland Score. The combination of biomarkers with hepcidin-25 may further improve diagnostic discrimination.

Proteinuria-take a closer look!

Proteinuria is a hallmark of kidney disease. Therefore, measurement of urine protein content plays a central role in any diagnostic work-up for kidney disease. In many cases, proteinuria analysis is restricted to the measurement of total protein content knowing that very high levels of proteinuria (nephrotic proteinuria) are characteristic of glomerular disease. Still, proteinuria can also be a manifestation of impaired tubular protein reabsorption or even be physiological. This review will discuss the physiology of renal protein handling and give guidance on a more sophisticated analysis of proteinuria differentiating albumin, low-molecular weight proteins and immunoglobulins. These non-invasive tests are available in most routine clinical laboratories and may guide the clinician in the diagnostic process before ordering far more expensive (molecular genetic testing) and/or invasive (kidney biopsy) diagnostics.

P-NGAL Day 1 predicts early but not one year graft function following deceased donor kidney transplantation - The CONTEXT study

BACKGROUND

Early markers to predict delayed kidney graft function (DGF) may support clinical management. We studied the ability of four biomarkers (neutrophil gelatinase associated lipocalin (NGAL), liver-type fatty acid-binding protein (L-FABP), cystatin C, and YKL-40) to predict DGF after deceased donor transplantation, and their association with early graft function and GFR at three and twelve months.

METHODS

225 deceased donor kidney transplant recipients were included. Biomarkers were measured using automated assays or ELISA. We calculated their ability to predict the need for dialysis post-transplant and correlated with the estimated time to a 50% reduction in plasma creatinine (tCr50), measured glomerular filtration rate (mGFR) and estimated GFR (eGFR).

RESULTS

All biomarkers measured at Day 1, except urinary L-FABP, significantly correlated with tCr50 and mGFR at Day 5. Plasma NGAL at Day 1 and a timed urine output predicted DGF (AUC = 0.91 and AUC 0.98). Nil or only weak correlations were identified between early biomarker levels and mGFR or eGFR at three or twelve months.

CONCLUSION

High plasma NGAL at Day 1 predicts DGF and is associated with initial graft function, but may not prove better than P-creatinine or a timed urine output. Early biomarker levels do not correlate with one-year graft function.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01395719.

Proteomics and Metabolomics for AKI Diagnosis

Acute kidney injury (AKI) is a severe and frequent condition in hospitalized patients. Currently, no efficient therapy of AKI is available. Therefore, efforts focus on early prevention and potentially early initiation of renal replacement therapy to improve the outcome in AKI. The detection of AKI in hospitalized patients implies the need for early, accurate, robust, and easily accessible biomarkers of AKI evolution and outcome prediction because only a narrow window exists to implement the earlier-described measures. Even more challenging is the multifactorial origin of AKI and the fact that the changes of molecular expression induced by AKI are difficult to distinguish from those of the diseases associated or causing AKI as shock or sepsis. During the past decade, a considerable number of protein biomarkers for AKI have been described and we expect from recent advances in the field of omics technologies that this number will increase further in the future and be extended to other sorts of biomolecules, such as RNAs, lipids, and metabolites. However, most of these biomarkers are poorly defined by their AKI-associated molecular context. In this review, we describe the state-of-the-art tissue and biofluid proteomic and metabolomic technologies and new bioinformatics approaches for proteomic and metabolomic pathway and molecular interaction analysis. In the second part of the review, we focus on AKI-associated proteomic and metabolomic biomarkers and briefly outline their pathophysiological context in AKI.

Short-term Changes in Urine Beta 2 Microglobulin Following Recovery of Acute Kidney Injury Resulting From Snake Envenomation

Introduction

Urine β2 microglobulin (β2m) is a validated marker to diagnose sepsis and toxin-related acute kidney injury (AKI). In the current study, we used urine β2m as a potential marker to identify persistent tubular dysfunction following a clinical recovery from snake venom–related AKI.

Methods

A total of 42 patients who developed AKI following hemotoxic envenomation were followed up for a period of 6 months. Urine albumin excretion, estimated glomerular filtration rate (eGFR), and urine β2m levels were measured at 2 weeks, 3 months, and 6 months following discharge.

Results

At the end of 6 months of follow-up, 6 patients (14.3 %) progressed to chronic kidney disease (CKD) (eGFR < 60 ml and/or urine albumin excretion > 30 mg/d). The urine β2m levels were 1590 μg/l (interquartile range [IQR] 425–5260), 610 μg/l (IQR 210–1850), 850 μg/l (IQR 270–2780) at 2 weeks, 3 months, and 6 months, respectively (P = 0.020). The levels of urine β2m in the study population at the end of 6 months remained significantly higher compared with the levels in healthy control population (850 μg/l [IQR 270–2780] vs. 210 μg/l [IQR 150–480]; P = 0.001). The proportion of patients with urine β2m levels exceeding the 95th percentile of control population (>644 µg/l) during the 3 follow-up visits were 70.7% (n = 29), 48.8 % (n = 20), and 51.2% (n = 21). Similar trends were noticed in a sensitivity analysis, after excluding patients with CKD.

Conclusions

Urine β2m levels remain persistently elevated in approximately half of the individuals who recover from AKI due to snake envenomation.

Using the newer Kidney Disease: Improving Global Outcomes criteria, beta-2-microglobulin levels associate with severity of acute kidney injury

Beta-2-microglobulin (B2M) is a marker of proximal tubular injury and glomerular filtration. Analyses using older/non-standardized definitions have shown low efficacy of B2M to predict acute kidney injury (AKI). We assessed if elevated levels of B2M would associate with either the diagnosis of AKI [under current Kidney Disease: Improving Global Outcomes (KDIGO) criteria] or recovery from AKI. We performed a retrospective study, including children who had urine B2M (uB2M) and/or serum B2M (sB2M) measured by immunoturbidimetry in our clinical laboratory between January 2011 and December 2015. We defined AKI based on KDIGO criteria [increase of serum creatinine (sCr) 0.3 mg/dL over 48 h or >50% baseline over 7 days] or urine output <0.5 mL/kg/h for 24 h. Recovery from AKI was defined as a return to baseline sCr within 6 months. We calculated receiver operating characteristics (ROC) area under the curve (AUC). Of 529 patients, 245 developed AKI. Serum and uB2M associated with AKI development (AUCs 0.84 and 0.73, respectively). Patients had a graded higher median sB2M and uB2M with each higher AKI stage. sB2M differentiated Stage I from Stage III AKI (P < 0.001) and Stage II from Stage III AKI (P = 0.004). However, neither uB2M nor sB2M levels associated with recovery from AKI. Only older age {hazard ratio [HR] 0.97, [95% confidence interval (CI) 0.94-0.99]} and need for dialysis [HR 0.39 (95% CI 0.23-0.61)] predicted incomplete recovery after AKI. Using KDIGO criteria, sB2M and uB2M associate with the severity of AKI. Given its relative ease and lower cost, we suggest more widespread use of B2M for AKI detection.

Evaluation of Urinary Renal Biomarkers for Early Prediction of Acute Kidney Injury Following Partial Nephrectomy: A Feasibility Study

BACKGROUND

Partial nephrectomy (PN) is the gold standard for the treatment of small renal masses. Urinary biomarkers (UBMs) may serve as early indicators of acute kidney injury (AKI) following PN.

OBJECTIVE

To evaluate the timing, specificity, and sensitivity of several candidate UBMs after PN to determine the most promising UBMs in this setting. We hypothesize that some UBMs will have utility as early markers of AKI.

DESIGN, SETTING, AND PARTICIPANTS

Twenty-two patients undergoing on-clamp robotic or open PN underwent paired urine collection via ureteral catheterization of the affected kidney and Foley catheterization for the unaffected kidney obtained preoperatively, after anesthesia, and at several points in time after renovascular occlusion.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Measured UBMs included albumin, α-glutathione S-transferase, B2M, calbindin, clusterin, cystatin C, epidermal growth hormone, kidney injury molecule 1, neutrophil gelatinase-associated lipocalin, osteoactivin, osteopontin, total protein, trefoil factor 3, uromodulin, and vascular endothelial growth factor.

RESULTS AND LIMITATIONS

The largest fold changes in UBM levels were observed between the baseline values and just prior to vascular occlusion (time "0"). Albumin, clusterin, and calbindin were among the most consistently and significantly increased UBMs. After vascular occlusion and subsequent reperfusion, some UBMs, most notably albumin, calbindin, and total protein, continued to increase in the affected kidney, peaking at 60-90min, followed by decrease to time "0" measurements after 1 d and to baseline levels 14-42 d after surgery. No striking association of UBMs with parameters such as duration of surgery, ischemia time, and tumor complexity was observed.

CONCLUSIONS

The most significant UBM increases were observed when comparing samples obtained at preoperative visit and after anesthesia, but before clamp time. Albumin, clusterin, and calbindin were the most consistently and significantly altered UBMs; further investigation will be necessary to determine whether UBMs can identify AKI earlier in nephrectomy patients.

PATIENT SUMMARY

Factors (biomarkers) measured in the blood or urine can indicate the presence and amount of kidney injury. We evaluated 15 different biomarkers at several points in time prior to, during, and after surgery for kidney cancer. We found that three of these biomarkers were most consistently elevated in patients undergoing partial nephrectomy. Interestingly, the largest increases were observed when comparing samples obtained prior to surgery with those obtained just after anesthesia.

Biomarkers in acute kidney injury (AKI)

Acute kidney injury is common in critically ill patients and portends a significant impact on mortality, progressive chronic kidney disease, and cardiovascular disease and mortality. Though most physicians alter therapy depending on changes in serum creatinine, this often represents delayed intervention. Various AKI biomarkers have been discovered and validated to improve timely detection, differentiation and stratification into risk groups for progressive renal decline, need for renal replacement therapy or death. This chapter will review AKI biomarkers validated over the past decade. We also describe the clinical performance of the biomarkers. We suggest that using AKI biomarkers to complement serum creatinine (or cystatin C) and urine output will better integrate patient care through earlier recognition and clinical outcome prediction after AKI.

Utility of cystatin C-based equations in patients undergoing dialysis

Serum cystatin C (CysC) measurement is regarded as a simple and practical alternative to measure residual renal function for dialysis patients. Recent studies have shown that CysC has better diagnostic accuracy or at least equivalence to creatinine in predicting the early stages of renal damage, and is closely related to clinical outcomes of dialysis patients. Thus, the applicability of CysC-derived equations in patients undergoing dialysis should be paid attention. Here, we review the role of CysC in diagnosis, renal function evaluation, and prognosis outcomes for dialysis patients, so as to provide them with useful suggestions on evaluating renal function and predicting adverse outcomes in clinical practice.

Cystatin C Is a More Reliable Biomarker for Determining eGFR to Support Drug Development Studies

Glomerular filtration rate (GFR) is routinely used as a surrogate endpoint for the development of investigational drugs in clinical trials. GFR and staging of chronic kidney disease are typically assessed by measuring the concentration of endogenous serum biomarkers such as albumin and creatinine. However, creatinine is subject to high biological variability, and levels of creatinine do not rise until nearly 50% of kidney function is damaged, leading to inaccurate chronic kidney disease staging and false negatives. A newer biomarker for GFR, cystatin C, has been shown to be subject to less biological interference and more sensitive to early declines in kidney function. Cystatin C has also been shown to outperform creatinine as an indicator of true GFR and to add information about the occurrence of acute kidney injury. Comparison studies of cystatin C and creatinine continue to demonstrate its increased accuracy and sensitivity for changes in true GFR. While challenges remain for use of cystatin C, international agencies and working groups continue to validate cystatin C as a biomarker and accompanying GFR estimating equations for diagnostic and drug development use. In this review, we summarize these comparison studies, regulatory and industry guidelines, and clinical trial case studies for use of cystatin C in drug development.

Biomarkers for prediction of renal replacement therapy in acute kidney injury: a systematic review and meta-analysis

Purpose

Acute kidney injury (AKI) frequently occurs in critically ill patients and often precipitates use of renal replacement therapy (RRT). However, the ideal circumstances for whether and when to start RRT remain unclear. We performed evidence synthesis of the available literature to evaluate the value of biomarkers to predict receipt of RRT for AKI.

Methods

We conducted a PRISMA-guided systematic review and meta-analysis including all trials evaluating biomarker performance for prediction of RRT in AKI. A systematic search was applied in MEDLINE, Embase, and CENTRAL databases from inception to September 2017. All studies reporting an area under the curve (AUC) for a biomarker to predict initiation of RRT were included.

Results

Sixty-three studies comprising 15,928 critically ill patients (median per study 122.5 [31–1439]) met eligibility. Forty-one studies evaluating 13 different biomarkers were included. Of these biomarkers, neutrophil gelatinase-associated lipocalin (NGAL) had the largest body of evidence. The pooled AUCs for urine and blood NGAL were 0.720 (95% CI 0.638–0.803) and 0.755 (0.706–0.803), respectively. Blood creatinine and cystatin C had pooled AUCs of 0.764 (0.732–0.796) and 0.768 (0.729–0.807), respectively. For urine biomarkers, interleukin-18, cystatin C, and the product of tissue inhibitor of metalloproteinase-2 and insulin growth factor binding protein-7 showed pooled AUCs of 0.668 (0.606–0.729), 0.722 (0.575–0.868), and 0.857 (0.789–0.925), respectively.

Conclusion

Though several biomarkers showed promise and reasonable prediction of RRT use for critically ill patients with AKI, the strength of evidence currently precludes their routine use to guide decision-making on when to initiate RRT.

Electronic supplementary material

The online version of this article (10.1007/s00134-018-5126-8) contains supplementary material, which is available to authorized users.

Fluid and Volume Monitoring

Background

Fluid resuscitation is not only used to prevent acute kidney injury (AKI) but fluid management is also a cornerstone of treatment for patients with established AKI and renal failure. Ultrafiltration removes volume initially from the intravascular compartment inducing a relative degree of hypovolemia. Normal reflex mechanisms attempt to sustain blood pressure constant despite marked changes in blood volume and cardiac output. Thus, compensated shock with a normal blood pressure is a major cause of AKI or exacerbations of AKI during ultrafiltration.

Methods

We undertook a systematic review of the literature using MEDLINE, Google Scholar and PubMed searches. We determined a list of key questions and convened a 2-day consensus conference to develop summary statements via a series of alternating breakout and plenary sessions. In these sessions, we identified supporting evidence and generated clinical practice recommendations and/or directions for future research.

Results

We defined three aspects of fluid monitoring: i) normal and pathophysiological cardiovascular mechanisms; ii) measures of volume responsiveness and impending cardiovascular collapse during volume removal, and; iii) measured indices of each using non-invasive and minimally invasive continuous and intermittent monitoring techniques. The evidence documents that AKI can occur in the setting of normotensive hypovolemia and that under-resuscitation represents a major cause of both AKI and mortality ion critically ill patients. Traditional measures of intravascular volume and ventricular filling do not predict volume responsiveness whereas dynamic functional hemodynamic markers, such as pulse pressure or stroke volume variation during positive pressure breathing or mean flow changes with passive leg raising are highly predictive of volume responsiveness. Numerous commercially-available devices exist that can acquire these signals.

Conclusions

Prospective clinical trials using functional hemodynamic markers in the diagnosis and management of AKI and volume status during ultrafiltration need to be performed. More traditional measure of preload be abandoned as marked of volume responsiveness though still useful to assess overall volume status.

Urine biomarkers give early prediction of acute kidney injury and outcome after out-of-hospital cardiac arrest

Background

Post-resuscitation care after out-of-hospital cardiac arrest (OHCA) is challenging due to the threat of organ failure and difficult prognostication. Our aim was to examine whether urine biomarkers could give an early prediction of acute kidney injury (AKI) and outcome.

Methods

This was a prospective observational study of comatose OHCA patients at Oslo University Hospital Ullevål, Norway. Risk factors were clinical parameters and biomarkers measured in spot urine (cystatin C, neutrophil gelatinase-associated lipocalin (NGAL) and the product of tissue inhibitor of metalloproteinase 2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7)) at admission and day 3. Outcome variables were AKI within 3 days using the Kidney Disease Improving Global Outcomes definition, 6-month mortality, and poor neurological outcome (PNO) defined as cerebral performance category 3–5.

Results

Among 195 included patients (85 % males, mean age 60 years), 88 (45 %) died, 96 (49 %) had PNO, and 88 (45 %) developed AKI. In univariate analysis, increased urine cystatin C and NGAL concentration sampled at admission and day 3 were independent risk factors for AKI, mortality and PNO. Increased urine TIMP-2 × IGFBP7 levels was associated with AKI only at admission. In multivariate analyses combining clinical parameters and biomarker concentrations, the area under the receiver operating characteristics curve (AuROC) with 95 % confidence interval (CI) were 0.774 (0.700–0.848), 0.812 (0.751–0.873), and 0.819 (0.759–0.878) for AKI, mortality and PNO, respectively.

Conclusions

In comatose OHCA patients, urine levels of cystatin C and NGAL at admission and day 3 were independent risk factors for AKI, 6-month mortality and PNO.

Trial registration

Clinicaltrials.gov NCT01239420. Registered 10 November 2010.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1503-2) contains supplementary material, which is available to authorized users.

Acute Kidney Injury and Cardiorenal Syndromes in Pediatric Cardiac Intensive Care

OBJECTIVES

The objectives of this review are to discuss the definition, diagnosis, and pathophysiology of acute kidney injury and its impact on immediate, short-, and long-term outcomes. In addition, the spectrum of cardiorenal syndromes will be reviewed including the pathophysiology on this interaction and its impact on outcomes.

DATA SOURCE

MEDLINE and PubMed.

CONCLUSION

The field of cardiac intensive care continues to advance in tandem with congenital heart surgery. As mortality has become a rare occurrence, the focus of cardiac intensive care has shifted to that of morbidity reduction. Acute kidney injury adversely impact outcomes of patients following surgery for congenital heart disease as well as in those with heart failure (cardiorenal syndrome). Patients who become fluid overloaded and/or require dialysis are at a higher risk of mortality, but even minor degrees of acute kidney injury portend a significant increase in mortality and morbidity. Clinicians continue to seek methods of early diagnosis and risk stratification of acute kidney injury to prevent its adverse sequelae.

Current Paradigm for Ischemia in Kidney Surgery

PURPOSE

Partial nephrectomy is the accepted standard of care for treatment of patients with small renal masses. The primary goal while performing partial nephrectomy is cancer control with a secondary important goal of maximizing renal function preservation with minimal perioperative morbidity. Recent studies have highlighted the importance of renal parenchymal quality and quantity postoperatively rather than duration of ischemia in determining long-term renal function. We review the available data regarding perioperative renal function optimization with special interest in ischemia during partial nephrectomy, highlighting the controversies and establishing future lines of investigation.

MATERIALS AND METHODS

We performed a comprehensive literature review for the years 1970 to 2014 via MEDLINE(®), PubMed(®) and the Cochrane Library. Review was consistent with the PRISMA (Preferred Reporting Items for Systemic Reviews and Meta-Analyses) criteria. We used MeSH (Medical Subject Headings) terms for the search including "acute kidney injury/failure," "carcinoma, renal cell/carcinoma of kidney/neoplasm of kidney," "kidney failure, chronic/end-stage kidney disease," "ischemia-reperfusion" and "warm ischemia/cold ischemia." Relevant review articles were included. Abstracts from major urological/surgical conferences were reviewed. All studies included were performed in adults, were written in English and had an abstract available.

RESULTS

Our traditional knowledge of renal ischemia is derived from animal studies, ie kidney transplant and retrospective partial nephrectomy series that indicate the risk of renal function impairment for every minute of ischemia. Careful evaluation of historical studies highlights flaws of the use of ischemia duration as a dichotomous marker (25 or 30 minutes) while predicting renal function outcomes. Recent studies have revealed no effect of duration of ischemia on ultimate kidney function in the short or long term. Quality and quantity of parenchyma preserved postoperatively are key predictors of ultimate renal function after partial nephrectomy. Traditionally partial nephrectomy has been performed with hilar occlusion to provide a relatively bloodless surgical field allowing effective oncologic control during tumor excision with secure management of blood vessels, collecting system and renal reconstruction. Selective clamping and nonclamping techniques have been proposed to avoid the perceived harmful effects of ischemia, although they convert a complex surgery into a more challenging procedure, potentially limiting the widespread use of partial nephrectomy for management of renal cancers. Promising urine and blood-based biomarkers (NGAL, KIM-1) in the context of critical care settings and global stress have been observed to predict acute kidney injury. Within the partial nephrectomy environment the usefulness of those markers needs to be further investigated. To date, no study has proved their usefulness in the setting of partial nephrectomy.

CONCLUSIONS

Based on the available evidence, use of a single cutoff for duration of ischemia time as a dichotomous value for renal function outcomes in the setting of partial nephrectomy is flawed. Renal ischemia is a controversial topic with a shifted paradigm within the last decade. Current evidence has shown that patients with 2 kidneys undergoing nephron sparing surgery can tolerate ischemia times of more than 30 minutes without a clinically significant decline in renal function. Biomarkers predictive of renal tubular injury fail to predict acute kidney injury in the context of partial nephrectomy. Indications for partial nephrectomy could be significantly expanded as the safety of limited renal ischemia is now better understood.

Urine exoglycosidases are potential markers of renal tubular injury in children with ureteropelvic junction obstruction

AIM

Hydronephrosis caused by ureteropelvic junction obstruction (UPJO) is an important problem in children and young adults. The aim of this pilot study was to determine the urine profiles of a number of lysosomal exoglycosidases to see whether they indicated tubular renal damage in children with UPJO.

METHODS

We measured lysosomal exoglycosidases urine activities in 32 patients with UPJO, dividing them into three groups. The surgical group comprised 16 children with severe hydronephrosis who required surgery, the nonsurgical group comprised 16 patients with mild hydronephrosis, and the reference group comprised 42 healthy children. The following indicators were measured: N-acetyl-β-hexosaminidase and its A and B isoenzymes, α-fucosidase, β-galactosidase, α-mannosidase and β-glucuronidase.

RESULTS

The urine activities of all exoglycosidases were significantly higher in children with UPJO than children in the reference group (p < 0.01). A strong positive correlation was also found between most of the urine exoglycosidases and the urine albumin/creatinine ratio (p < 0.01).

CONCLUSION

Our findings demonstrated that children with UPJO showed increased renal activities of assessed exoglycosidases, which correlated positively with the urine albumin/creatinine ratio. A larger multicentre study is required to confirm the clinical applications of these observations.

The potential utility of urinary biomarkers for risk prediction in combat casualties: a prospective observational cohort study

Introduction

Traditional risk scoring prediction models for trauma use either anatomically based estimations of injury or presenting vital signs. Markers of organ dysfunction may provide additional prognostic capability to these models. The objective of this study was to evaluate if urinary biomarkers are associated with poor outcomes, including death and the need for renal replacement therapy.

Methods

We conducted a prospective, observational study in United States Military personnel with traumatic injury admitted to the intensive care unit at a combat support hospital in Afghanistan.

Results

Eighty nine patients with urine samples drawn at admission to the intensive care unit were studied. Twelve patients subsequently died or needed renal replacement therapy. Median admission levels of urinary cystatin C (CyC), interleukin 18 (IL-18), L-type fatty acid binding protein (LFABP) and neutrophil gelatinase-associated lipocalin (NGAL) were significantly higher in patients that developed the combined outcome of death or need for renal replacement therapy. Median admission levels of kidney injury molecule-1 were not associated with the combined outcome. The area under the receiver operating characteristic curves for the combined outcome were 0.815, 0.682, 0.842 and 0.820 for CyC, IL-18, LFABP and NGAL, respectively. Multivariable regression adjusted for injury severity score, revealed CyC (OR 1.97, 95 % confidence interval 1.26-3.10, p = 0.003), LFABP (OR 1.92, 95 % confidence interval 1.24-2.99, p = 0.004) and NGAL (OR 1.80, 95 % confidence interval 1.21-2.66, p = 0.004) to be significantly associated with the composite outcome.

Conclusions

Urinary biomarker levels at the time of admission are associated with death or need for renal replacement therapy. Larger multicenter studies will be required to determine how urinary biomarkers can best be used in future prediction models.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0965-y) contains supplementary material, which is available to authorized users.

Novel biomarkers of acute kidney injury: Evaluation and evidence in urologic surgery

Patients undergoing urologic surgery are at risk of acute kidney injury (AKI) and consequently long-term deterioration in renal function. AKI is further associated with significantly higher odds of perioperative complications, prolonged hospital stay, higher mortality and costs. Therefore, better awareness and detection of AKI, as well as identification of AKI determinants in the urological surgery setting is warranted to pre-empt and mitigate further deterioration of renal function in patients at special risk. New consensus criteria provide precise definitions of diagnosis and description of the severity of AKI. However, they rely on serum creatinine (SCr), which is known to be an inaccurate marker of early changes in renal function. Therefore, several new urinary and serum biomarkers promise to address the gap associated with the use of SCr. Novel biomarkers may complement SCr measurement or most likely improve the diagnostic accuracy of AKI when used in combinations. However, novel biomarkers have to prove their clinical applicability, accuracy, and cost effectiveness prior to implementation into clinical practice. Most preferably, novel biomarkers should help to positively improve a patient’s long-term renal functional outcomes. The purpose of this review is to discuss currently available biomarkers and to review their clinical evidence within urologic surgery settings.

Paediatric single mitochondrial DNA deletion disorders: an overlapping spectrum of disease

BACKGROUND

Single large-scale mitochondrial DNA (mtDNA) deletions (SLSMDs) are amongst the most frequently diagnosed mtDNA disorders in childhood, yet their natural history remains poorly understood. We report the natural history of a large multicentre cohort of such children.

METHODS

We reviewed case notes from three different UK centres to determine the clinical course of 34 patients (16 female, 18 male) with childhood-onset mitochondrial disease caused by SLSMDs. Kaplan-Meier analysis was used to compare survival of patients presenting with haematological features (Pearson syndrome) and those with nonhaematological presentations.

RESULTS

The most frequent initial presentation was with isolated ptosis (16/34, 47%). Eleven (32%) patients presented with transfusion-dependent anaemia soon after birth and were diagnosed with Pearson syndrome, whilst ten were classified as having Kearns-Sayre syndrome, three as having progressive external ophthalmoplegia (PEO) and seven as having PEO-plus. Three patients did not conform to any specific mitochondrial syndrome. The most frequently affected organ during the disease course was the kidney, with documented tubular or glomerular dysfunction in 17 of 20 (85%) cases who had detailed investigations. SLSMDs were present in blood and/or urine cells in all cases tested, indicating that muscle biopsy is not necessary for diagnosis in the paediatric age range. Kaplan-Meier survival analysis revealed significantly worse mortality in patients with Pearson syndrome compared with the rest of the cohort.

CONCLUSIONS

Mitochondrial disease caused by SLSMDs is clinically heterogeneous, and not all cases conform to a classical mitochondrial syndrome. Multisystem disease is the norm, with anaemia, renal impairment and endocrine disturbance being the most frequent extraneurological features. SLSMDs should be considered in the differential diagnosis of all children presenting with ptosis.

Eculizumab reduces complement activation, inflammation, endothelial damage, thrombosis, and renal injury markers in aHUS

Atypical hemolytic uremic syndrome (aHUS) is a genetic, life-threatening disease characterized by uncontrolled complement activation, systemic thrombotic microangiopathy (TMA), and vital organ damage. We evaluated the effect of terminal complement blockade with the anti-C5 monoclonal antibody eculizumab on biomarkers of cellular processes involved in TMA in patients with aHUS longitudinally, during up to 1 year of treatment, compared with in healthy volunteers. Biomarker levels were elevated at baseline in most patients, regardless of mutational status, plasma exchange/infusion use, platelet count, or lactate dehydrogenase or haptoglobin levels. Eculizumab reduced terminal complement activation (C5a and sC5b-9) and renal injury markers (clusterin, cystatin-C, β2-microglobulin, and liver fatty acid binding protein-1) to healthy volunteer levels and reduced inflammation (soluble tumor necrosis factor receptor-1), coagulation (prothrombin fragment F1+2 and d-dimer), and endothelial damage (thrombomodulin) markers to near-normal levels. Alternative pathway activation (Ba) and endothelial activation markers (soluble vascular cell adhesion molecule-1) decreased but remained elevated, reflecting ongoing complement activation in aHUS despite complete terminal complement blockade. These results highlight links between terminal complement activation and inflammation, endothelial damage, thrombosis, and renal injury and underscore ongoing risk for systemic TMA and progression to organ damage. Further research regarding underlying complement dysregulation is warranted. This trial was registered at www.clinicaltrials.gov as #NCT01194973.

Urinary kidney biomarkers for early detection of nephrotoxicity in clinical drug development

Early detection of drug-induced kidney injury is vital in drug development. Generally accepted biomarkers such as creatinine and blood urea nitrogen (BUN) lack sensitivity and early injury responses are missed. Many new biomarkers to detect nephrotoxicity for pre-clinical utilization have been described and their use is adopted in regulatory guidelines. However, guidance on appropriate biomarkers for clinical trials is minimal. We provide an overview of potentially useful kidney biomarkers that can be used in clinical trials. This includes guidance to select biomarkers suitable to capture specific characteristics of the (expected) kidney injury. We conclude that measurement of urinary kidney injury marker-1 (KIM-1) serves many purposes and is often an appropriate choice. Cystatin C captures effects on glomerular filtration rate (GFR), but this marker should preferably be combined with more specific markers to localize the origin of the observed effect. Untoward effects on tubules can be captured relatively well with several markers. Direct detection of glomerular injury is currently impossible since specific biomarkers are lacking. Indirect assessment of toxic effects on glomeruli is possible by using carefully selected panels of other injury markers. We conclude that it is possible to obtain appropriate information on nephrotoxicity in clinical drug development by using carefully selected panels of injury markers and suggest that identification and validation of specific glomerular biomarkers could be of great value.

The significance of tubular and glomerular proteinuria in critically ill patients with severe acute kidney injury

OBJECTIVE

Critically ill patients with acute kidney injury (AKI) frequently need acute renal replacement therapy (aRRT). We evaluated an inexpensive, rapid quantitative and qualitative analysis of proteinuria on the course of AKI patients requiring aRRT in intensive care.

METHOD

This was a prospective, observational study of critically ill patients with severe established AKI or Acute on Chronic Kidney Injury (AoCKI) requiring aRRT. Urine samples were analyzed using Sodium-Dodecyl-Sulphate-Polyacryamide Gel Electrophoresis (SDS-PAGE).

RESULTS

A total of 30 critically ill patients were studied. Those who died have higher APACHE II (29 ± 6 vs. 20 ± 5, p<0.001), multi-organ failure (0.7 ± 0.5 vs. 0.2 ± 0.4, p < 0.02) and Tubular/Glomerular ratio (114 ± 60 vs. 75± 37, p < 0.05).The renal non-recoverers have higher baseline creatinine (415 ± 328 vs. 125± 19 umol/l, p < 0.01), urinary Dipstick value (1.8±0.8 vs. 0.5±0, p <0.05) and Glomerular score (3.0 ± 1.8 vs. 0.6 ± 0.2, p < 0.02).Heavy tubular proteinuria also predicts a longer duration of interim dialysis support and mortality whereas glomerular proteinuria correlates with development of chronicity and End Stage Renal Disease (ESRD).

CONCLUSIONS

The dominant presence of tubular proteinuria is associated with poor survival in patients who have high APACHE II score and multi-organ failure. It also correlates with a longer duration of dialysis support in survivals. Renal Non-recoverers had heavy dominant presence of glomerular proteinuria. SDS-PAGE proteinuria analysis offers a reliable and inexpensive method to prognosticate proteinuria in this group of critically ill patients.

Normalisation of urinary biomarkers to creatinine for clinical practice and research--when and why

Acute kidney injury (AKI) and chronic kidney disease (CKD) are major health problems. Urinary biomarkers have both diagnostic and prognostic utility in AKI and CKD. However, how biomarker excretion rates should be reported, especially whether they should be normalised to urinary creatinine concentration (uCr), is controversial. Some studies suggest that normalisation to uCr may be inappropriate at times, as urinary creatinine excretion rate may vary greatly, depending on the situation. Notably, recent studies suggest that while normalisation of values to UCr may be valid for the evaluation of CKD and prediction of AKI sequelae and occurrences, it could be inappropriate for the diagnosis of AKI, or in the presence of certain acute kidney disease states.

Cystatin C for early detection of acute kidney injury after laparoscopic partial nephrectomy

Introduction and Objectives:

Mortality due to AKI has not changed significantly over the past 50 years. This is due in part to failure to detect early AKI and to initiate appropriate therapeutic measures. There is therefore a need to identify biomarkers that would improve the early detection of AKI. The objective of this study was to assess whether cystatin C levels obtained at specific timepoints during laparoscopic partial nephrectomy (PN) could be early predictors of AKI.

Materials and Methods:

Twenty-five patients underwent laparoscopic PN for organ-confined tumors. All procedures were performed by two surgeons in a single institution. Plasma samples were collected preoperatively, and post-unclamping at 5, 20, 120 min and on the day following surgery. Plasma cystatin C was measured by enzyme-linked immunosorbent assay. Correlation between levels of cystatin C and other parameters of interest were assessed in order to define cystatin C ability to predict AKI and loss of renal function following laparoscopic PN.

Results:

The mean baseline eGFR was 93 ml/min/1.73 m². Warm ischemia time varied between 16 and 44 min. Post-operative day 1 (POD1) cystatin C levels compared to baseline were increased in 13 (52%) of the patients. There was a high correlation between the difference of POD 1 and baseline value, and eGFR in the immediate postoperative period (r = −0.681; P = 0.0002) and at 12-month follow-up (r = −0.460, P = 0.048). However, the variation in cystatin C levels at earlier timepoints were not associated to AKI nor renal function.

Conclusions:

High increase in POD 1 cystatin C levels from baseline may help identify patients with AKI and those at higher risk of chronic kidney disease, following laparoscopic PN.

Cystatin C: a new renal marker and its potential use in small animal medicine

The occurrence of chronic kidney disease is underestimated in both human and veterinary medicine. Glomerular filtration rate (GFR) is considered the gold standard for evaluating kidney function. However, GFR assessment is time-consuming and labor-intensive and therefore not routinely used in practice. The commonly used indirect GFR markers, serum creatinine (sCr) and urea, are not sufficiently sensitive or specific to detect early renal dysfunction. Serum cystatin C (sCysC), a proteinase inhibitor, has most of the properties required for an endogenous GFR marker. In human medicine, numerous studies have evaluated its potential use as a GFR marker in several populations. In veterinary medicine, this marker is gaining interest. The measurement is easy, which makes it an interesting parameter for clinical use. This review summarizes current knowledge about cystatin C (CysC) in humans, dogs, and cats, including its history, assays, relationship with GFR, and biological and clinical variations in both human and veterinary medicine.

Drug-induced nephrotoxicity and its biomarkers

Nephrotoxicity occurs when kidney-specific detoxification and excretion do not work properly due to the damage or destruction of kidney function by exogenous or endogenous toxicants. Exposure to drugs often results in toxicity in kidney which represents the major control system maintaining homeostasis of body and thus is especially susceptible to xenobiotics. Understanding the toxic mechanisms for nephrotoxicity provides useful information on the development of drugs with therapeutic benefi ts with reduced side effects. Mechanisms for drug-induced nephrotoxicity include changes in glomerular hemodynamics, tubular cell toxicity, inflammation, crystal nephropathy, rhabdomyolysis, and thrombotic microangiopathy. Biomarkers have been identifi ed for the assessment of nephrotoxicity. The discovery and development of novel biomarkers that can diagnose kidney damage earlier and more accurately are needed for effective prevention of drug-induced nephrotoxicity. Although some of them fail to confer specificity and sensitivity, several promising candidates of biomarkers were recently proved for assessment of nephrotoxicity. In this review, we summarize mechanisms of drug-induced nephrotoxicity and present the list of drugs that cause nephrotoxicity and biomarkers that can be used for early assessment of nephrotoxicity.

Urinary lysosomal enzyme excretion in pregnant women with hypertensive disorders

BACKGROUND

The authors assessed proximal renal tubular dysfunction and/or damage in pregnant women with various types of hypertension by measuring the three urinary lysosomal enzyme levels: N-acetyl-β-d-glucosaminidase (NAG), arylsulfatase A and β-glucuronidase.

METHODS

The study consisted of 120 pregnant women divided into four groups: 41 women in 20th week of gestation or more, with pregnancy-induced hypertension (PIH group), 28 pregnant women after 20 weeks of pregnancy with pre-eclampsia (PE group), 21 pregnant women with chronic hypertension, identified before 20th week of pregnancy (CH group) and 30 healthy, pregnant women (healthy controls (HC) group).

RESULTS

Statistical analysis showed significantly higher levels of all the three of lysosomal enzymes in the urine of patients with PE compared with the healthy pregnant women, pregnant women with PIH and the ones with chronic hypertension. Additionally, significantly higher values of NAG were found in the group of pregnant women with PIH compared with healthy pregnancies. No correlation was found between the concentration of enzymes in urine and values of blood pressure in any of the analyzed groups of pregnant women.

CONCLUSIONS

The authors conclude that higher values of all the studied enzymes in PE group, in the comparison with the other groups, indicate proximal tubular damage at the cellular level. The lack of correlation between the concentration of lysosomal enzymes and blood pressure suggests that the damage to these parts of kidney is complex. In addition, mechanisms other than hypertension realizing intracellular enzymes may be involved in this process.

Urinary biomarkers in assessing the nephrotoxic potential of gentamicin in solitary kidney patients after 7 days of therapy

INTRODUCTION

The solitary kidney (SK) may present increased vulnerability to nephrotoxicity because of adaptive phenomena.

AIMS

Assessing the vulnerability of the SK with urinary tract infections (UTI) to gentamicin by means of urinary biomarkers (N-acetyl-beta-D-glucosaminidase (NAG) and urinary alpha-1-microglobulin), as well as glomerular filtration rate (GFR).

METHODS

We studied 14 patients with SK with UTI (group A) (mean age 58.07 ± 13.61 years, mean duration of SK 13.55 ± 12.33 years) who were administered gentamicin for 7 days. Group B consisted by 17 patients with SK without any other associated renal pathology (average age 51.17 ± 9.39 years, average existence period of a single kidney 33.23 ± 21.73 years). We also included a third group (group C) represented by nine healthy individuals, with two kidneys.

RESULTS

Increased values of urinary NAG were found in group B as compared to group C and alpha-1 microglobulin in group A as compared to group B. During treatment with gentamicin, increased values of both NAG and alpha-1-microglobulin in group A were found on day 7 as compared to values before treatment (day 7 NAG=18.99 ± 14.07 U/g creat versus day 0, NAG=5.15 ± 6.54 U/g creat, p=0.004; day 7 alpha-1-microglobulin=20.88 ± 18.84 mg/g creat versus day 0, urinary alpha-1-microglobulin=4.96 ± 6.57 mg/g creat, p=0.003). No statistically significant alterations of GFR were noticed after 7 days of treatment.

CONCLUSIONS

We found the nephrotoxic effects of gentamicin at tubular level, but not at glomerular level. The nephrotoxic potential of gentamicin in patients with a SK can be monitored by assessing urinary biomarkers during treatment of UTI.

Time of injury affects urinary biomarker predictive values for acute kidney injury in critically ill, non-septic patients

Background

The predictive value of acute kidney injury (AKI) urinary biomarkers may depend on the time interval following tubular injury, thereby explaining in part the heterogeneous performance of these markers that has been reported in the literature. We studied the influence of timing on the predictive values of tubular proteins, measured before the rise of serum creatinine (SCr) in critically ill, non-septic patients.

Methods

Seven hundred adult critically ill patients were prospectively included for urine measurements at four time-points prior to the rise in serum creatinine (T = 0, -16, -20 and -24 h). Patients with sepsis and or AKI at ICU entry were excluded. The urinary excretion of the proteins, neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1), which are up-regulated in the distal and proximal tubules, respectively, were measured as well as the constitutive cytoplasmatic enzymes, π- and α-glutathione-S-transferase (GST), which are released by the distal and proximal tubules, respectively.

Results

Five hundred and forty-three subjects were eligible for further analyses; however, 49 developed AKI in the first 48 h. Both NGAL (P = 0.001 at T = -24 vs. non-AKI patients) and KIM-1 (P < 0.0001 at T = 0 vs. non-AKI patients) concentrations gradually increased until AKI diagnosis, whereas π- and α-GST peaked at T = -24 before AKI (P = 0.006 and P = 0.002, respectively vs. non-AKI patients) and showed a rapid decline afterwards. The predictive values at T = -24 prior to AKI were modest for π- and α-GST, whereas NGAL sufficiently predicted AKI at T = -24 and its predictive power improved as the time interval to AKI presentation decreased (area under the receiver operating characteristic curve; AUC = 0.79, P < 0.0001). KIM-1 was a good discriminator at T = 0 only (AUC = 0.73, P < 0.0001).

Conclusions

NGAL, KIM-1, pi- and alpha-GST displayed unique and mutually incomparable time dependent characteristics during the development of non-sepsis related AKI. Therefore, the time-relationship between the biomarker measurements and the injurious event influences the individual test results.