Plasma neutrophil gelatinase-associated lipocalin is an early marker of acute kidney injury in adult critically ill patients: a prospective study

Biomarkers in cardiorenal syndrome

Cardiac and renal diseases often coexist. Treatment may prove difficult as early diagnosis and effective therapy may be hindered by a lack of robust markers of disease activity. However, several candidate molecules are now available which may help elucidate the complexities of organ cross-talk, enabling effective therapies. We discuss the available data on the commonly studied biomarkers of acute kidney injury with reference to the cardiorenal syndrome. Furthermore, we propose how the use of biomarkers as a panel may provide information which can guide therapy. Although this is a relatively new field, advances are rapid, and such options may well be available to the clinician soon.

Plasma and urine neutrophil gelatinase-associated lipocalin in the diagnosis of new onset acute kidney injury in critically ill patients

Introduction

Neutrophil gelatinase-associated lipocalin (NGAL) has been demonstrated to be a useful early diagnostic biomarker of acute kidney injury (AKI) where the timing of the insult is certain. However, NGAL is not well validated in adult critical care practice because of indeterminate timing of injury. Therefore, we sought to establish the predictive ability of both urine and plasma NGAL to detect AKI in ICU patients.

Method

This prospective observational study was performed in a busy large district general hospital mixed surgical-medical ICU in Reading, UK. Consecutive adult admissions to the ICU, with absence of chronic kidney disease, renal transplant or AKI as defined by RIFLE criteria were included. Blood and urine specimens were collected at admission and every 24 hours until 72 hours and tested for NGAL. The purpose of the study was to assess whether urinary NGAL (uNGAL) or plasma NGAL (pNGAL) can predict the occurrence of AKI at an earlier point of time than the conventional markers, that is creatinine and urine output as is used in RIFLE criteria.

Results

Over a 12-month period, 194 patients were enrolled. In total, 59 (30.4%) patients developed AKI. The admission pNGAL and uNGAL were significantly higher in the patients who developed AKI compared to the non-AKI patients (436 ng/mL (240, 797) versus 168 ng/mL (121.3, 274.3) P <0.001 and 342 ng/mL (61.5, 1,280) versus 34.5 ng/mL (11.5, 107.75) P <0.001 respectively). Hospital mortality was higher in the AKI group (17% versus 4%). Plasma NGAL performed fairly on admission (AUROC 0.77) and thereafter performance improved at 24 and 48 hours (AUROC 0.88 and 0.87) following ICU admission. Urine NGAL had a fair predictive value on admission (AUROC 0.79) and at 24 hours (AUROC 0.78) and was good at 48 hours (AUROC 0.82).

Conclusions

In critically ill patients without pre-existing kidney disease, both pNGAL and uNGAL measured at admission can predict AKI (defined by RIFLE criteria) occurrence up to 72 hours post-ICU admission and their performance (AUROC) was fair. The accuracy of NGAL appeared to improve slightly as patients progressed through their ICU stay. Serial measurements of NGAL (both pNGAL and uNGAL) may be of added value in an ICU setting to predict the occurrence of AKI.

Neutrophil gelatinase-associated lipocalin as a biomarker of acute kidney injury: a critical evaluation of current status

BACKGROUND

The early prediction of acute kidney injury (AKI) by current clinical and laboratory methods remains inadequate. Neutrophil gelatinase-associated lipocalin (NGAL) has emerged as a promising non-invasive biomarker of kidney injury. We systematically reviewed the utility of plasma and urine NGAL measurements for the prediction of AKI in humans.

METHODS

We searched MEDLINE, PubMed and EMBASE for human biomarker studies that included NGAL (January 2005 to October 2013). Studies reporting on the use of NGAL for the early prediction and prognosis of AKI were analysed in three common clinical settings: cardiac surgery, critical illness and kidney transplantation.

RESULTS

We identified 58 manuscripts that met our inclusion and exclusion criteria, reporting on more than 16,500 patients. Following cardiac surgery, NGAL measurement in over 7000 patients was predictive of AKI and its severity, with an overall area under the receiver operator characteristic curve (AUC) of 0.82-0.83. Similar results were obtained in over 8500 critically ill patients. In over 1000 patients undergoing kidney transplantation, NGAL measurements predicted delayed graft function with an overall AUC of 0.87. In all three settings, NGAL significantly improved the prediction of AKI risk over the clinical model alone.

CONCLUSIONS

We identified several studies that collectively strongly support the use of NGAL as a biomarker for the prediction of AKI. However, we noted some limitations, including lack of published studies that adhere to diagnostic study guidelines, heterogeneity in AKI definition, the lack of uniformly applicable cut-off values and variability in the performance of commercially available NGAL assays.

Neutrophil gelatinase-associated lipocalin in dogs with naturally occurring renal diseases

Background

Neutrophil gelatinase–associated lipocalin (NGAL) is released from renal tubular cells after injury and serves in humans as a real‐time indicator of active kidney damage, including acute kidney injury (AKI) and chronic kidney disease (CKD). However, NGAL concentrations in dogs with naturally occurring AKI or CKD rarely have been explored in detail.

Hypothesis/Objectives

The goal of this study was to evaluate whether NGAL can serve as a useful biomarker in dogs with naturally occurring renal disease.

Animals

Client‐owned dogs with renal disease (57) and control dogs without any disease (12) were examined.

Methods

Serum NGAL (sNGAL) and urine NGAL (uNGAL) concentrations were measured in each animal by a newly developed ELISA system. Demographic, hematologic, and serum biochemical data were recorded. Survival attributable to AKI and CKD was evaluated at 30 days and 90 days, respectively.

Results

Serum and urine NGAL concentrations in azotemic dogs were significantly higher than in nonazotemic dogs and were highly correlated with serum creatinine concentration (P < .05). Among CKD dogs, death was associated with significantly higher sNGAL and uNGAL concentrations compared with survivors. Receiver‐operating characteristic curve (ROC) analysis showed that sNGAL was better than serum creatinine concentration when predicting clinical outcomes for CKD dogs (P < .05). The best cutoff point for sNGAL was 50.6 ng/mL, which gave a sensitivity and a specificity of 76.9 and 100%, respectively. Furthermore, dogs that had higher concentrations of sNGAL survived for a significantly shorter time.

Conclusion

sNGAL is a useful prognostic marker when evaluating dogs with CKD.

Neutrophil gelatinase associated lipocalin in acute kidney injury

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) is a member of the lipocalin family of proteins. Usually, NGAL is produced and secreted by kidney tubule cells at low levels, but the amount produced and secreted into the urine and serum increases dramatically after ischemic, septic, or nephrotoxic injury of the kidneys. The purpose of our review article is to summarize the role of NGAL in acute kidney injury (AKI), emergent, and intensive care.

METHODS

A PubMed search was performed (only English-language articles concerning human subjects were considered) using each of the following search term combinations: neutrophil gelatinase-associated lipocalin OR NGAL and acute kidney injury OR AKI; cardiac surgery; heart failure OR cardiology; intensive care; emergency department OR emergency medicine; nephropathy OR nephrotoxicity and transplantation.

RESULTS

The results of our search yielded 339 articles. Of the 339 articles, 160 were eligible for review based on the predefined criteria for inclusion.

CONCLUSION

Based on the evidence reviewed, it is clear that patient NGAL level is an appropriate, sensitive, and specific early biomarker of AKI caused by a variety of different etiologies. It is advised that a multidisciplinary group of experts come together to make recommendations and propose a consensus of clinical procedures to advance the most efficacious NGAL monitoring protocol for early detection and treatment of patients with AKI.

Neutrophil gelatinase-associated lipocalin

PURPOSE OF REVIEW

Acute kidney injury (AKI) is a major clinical problem in hospitalized patients. Effective treatment and early diagnosis of this syndrome are not currently available. This review focuses on recent studies examining the biological characteristics and the diagnostic and prognostic value of a novel biomarker--neutrophil gelatinase-associated lipocalin (NGAL)--in the two major patient populations at risk for AKI.

RECENT FINDINGS

NGAL is one of the most intensively investigated novel renal biomarkers with promising data from animal experiments and clinical studies comprising more than 3500 cardiac surgery or critically ill patients. NGAL was discovered using unbiased transcriptomic approaches and was identified as the gene with the earliest and highest rise of mRNA and protein concentration in renal tissue, urine and plasma following various renal insults. Within minutes to a few hours after a renal insult, NGAL is induced in and released from the injured distal nephron. The average sensitivity and specificity of NGAL--measured 1-3 days prior to current AKI consensus diagnosis--was 76 and 77% respectively for cardiac surgery patients and 73 and 80% respectively for patients admitted to the intensive care unit.

SUMMARY

NGAL appears to fulfill many characteristics of an appropriate 'real-time' biomarker for AKI detection.

Plasma NGAL for the diagnosis of AKI in patients admitted from the emergency department setting

BACKGROUND AND OBJECTIVES

The purpose of this study was to determine the accuracy of plasma neutrophil gelatinase-associated lipocalin as a marker of AKI in patients admitted from the emergency department.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this prospective cohort study, patients (n=616) admitted from the emergency department from March to November of 2008 were classified according to clinical criteria as AKI, transient azotemia, stable CKD, and normal function. Plasma neutrophil gelatinase-associated lipocalin was measured serially. A logistic regression model using clinical characteristics was fitted to the data, and a second model included discretized plasma neutrophil gelatinase-associated lipocalin. Performance of the models was evaluated by Hosmer-Lemeshow goodness-of-fit test, area under the receiver operating characteristic curve, net reclassification improvement, integrated discrimination improvement, and predictiveness curve.

RESULTS

Twenty-one percent of patients were classified as AKI; the highest median levels of plasma neutrophil gelatinase-associated lipocalin were in the AKI group (146-174 ng/ml at various time points) and increased with AKI severity (207-244 ng/ml for Acute Kidney Injury Network classification stage>2). The discriminative ability of plasma neutrophil gelatinase-associated lipocalin for AKI diagnosis (area under the curve, 0.77-0.82 at various time points) improved with higher grades of severity (area under the curve, 0.85-0.89 for AKIN>2). Plasma neutrophil gelatinase-associated lipocalin discriminated AKI from normal function and transient azotemia (area under the curve, 0.85 and 0.73, respectively). Patients were classified into three grades of AKI risk according to plasma neutrophil gelatinase-associated lipocalin levels (low, moderate [i.e., the gray zone], and high). Patients with plasma neutrophil gelatinase-associated lipocalin in the high-risk category displayed a 10-fold greater risk of AKI (odds ratio, 9.8; 95% confidence interval, 5.6 to 16.9). The addition of plasma neutrophil gelatinase-associated lipocalin to the clinical model yielded a net reclassification improvement of 94.3% and an integrated discrimination improvement of 0.122.

CONCLUSION

Plasma neutrophil gelatinase-associated lipocalin is an accurate biomarker for prediction of AKI in patients admitted from the emergency department. This work proposes a three-grade classification of AKI risk based on plasma neutrophil gelatinase-associated lipocalin levels.

The nature and discriminatory value of urinary neutrophil gelatinase-associated lipocalin in critically ill patients at risk of acute kidney injury

BACKGROUND

Different molecular forms of urinary neutrophil gelatinase-associated lipocalin (NGAL) have recently been discovered. We aimed to explore the nature, source and discriminatory value of urinary NGAL in intensive care unit (ICU) patients.

METHODS

We simultaneously measured plasma NGAL (pNGAL), urinary NGAL (uNGAL), and estimated monomeric and homodimeric uNGAL contribution using Western blotting-validated enzyme-linked immunosorbent assays [uNGAL(E1) and uNGAL(E2)] and their calculated ratio in 102 patients with the systemic inflammatory response syndrome and oliguria, and/or a creatinine rise of >25 μmol/L.

MEASUREMENTS AND MAIN RESULTS

Bland-Altman analysis demonstrated that, despite correlating well (r = 0.988), uNGAL and uNGAL(E1) were clinically distinct, lacking both accuracy and precision (bias: 266.23; 95% CI 82.03-450.44 ng/mg creatinine; limits of agreement: -1,573.86 to 2,106.32 ng/mg creatinine). At best, urinary forms of NGAL are fair (area under the receiver operating characteristic [AUROC] ≤0.799) predictors of renal or patient outcome; most perform significantly worse. The 44 patients with a primarily monomeric source of uNGAL had higher pNGAL (118.5 ng/ml vs. 72.5 ng/ml; p < 0.001), remaining significant following Bonferroni correction.

CONCLUSIONS

uNGAL is not a useful predictor of outcome in this ICU population. uNGAL patterns may predict distinct clinical phenotypes. The nature and source of uNGAL are complex and challenge the utility of NGAL as a uniform biomarker.

Plasma neutrophil gelatinase-associated lipocalin and adverse outcome in critically ill patients with ventilatory support

OBJECTIVE

Plasma neutrophil gelatinase-associated lipocalin (pNGAL) has been introduced as an early and sensitive biomarker of acute kidney injury (AKI), with an increased risk for renal replacement therapy (RRT) and adverse outcome in selected critically ill patient groups. Acute respiratory failure is the most common organ dysfunction in critically ill patients with an increased risk for AKI. Accordingly, we hypothesized that pNGAL would independently predict adverse outcome in a heterogeneous group of critically ill adult patients with acute respiratory failure.

DESIGN AND SETTING

Prospective, multi-centre study in 25 Finnish intensive care units.

PATIENTS AND METHODS

pNGAL was measured from critically ill patients with acute respiratory failure. We evaluated the predictive value of pNGAL for RRT, and hospital and 90-day mortality first separately, second in addition to the Simplified Acute Physiology Score (SAPS II), and third to RIFLE (Risk, Injury, Failure, Loss, End-Stage Renal Disease) AKI classification. Additionally, we assessed the factors associated with pNGAL by linear regression analysis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We included 369 patients. Median (interquartile range) baseline pNGAL was 169 (92-370) ng/ml. The areas under receiver operating characteristic curves of baseline pNGAL were as follows: 0.733 [95% confidence interval (CI) 0.656-0.810] for RRT, 0.627 (95% CI 0.561-0.693) for hospital, and 0.582 (95% CI 0.520-0.645) for 90-day mortality. Present infection, baseline creatinine, operative status, and pancreatitis were independently associated with baseline pNGAL.

CONCLUSIONS

Baseline pNGAL gives no additional value into prediction of hospital and 90-day mortality compared with RIFLE or SAPS II, and has only moderate predictive power regarding RRT in critically ill adult patients with acute respiratory failure.

The clinical utility of plasma neutrophil gelatinase-associated lipocalin in acute kidney injury

BACKGROUND AND AIM

Neutrophil gelatinase-associated lipocalin (NGAL) is derived from the distal tubule and is both reabsorbed and filtered and also shed into the urine after tubular injury. Plasma NGAL is unique amongst the candidate biomarkers of acute kidney injury (AKI) since elevated concentrations may reflect either a change in renal glomerular function or in structural tubular injury or both. In this study, we compared the performance of plasma NGAL in the diagnosis of functional changes and in the diagnosis of structural injury.

METHODS

Plasma and urine samples from 528 patients were collected on entry to an intensive care unit (ICU) as well as 12 and 24 h later. Plasma NGAL diagnostic performance was independently assessed for Functional-AKI and Structural-AKI. Functional-AKI was defined by changes in plasma creatinine, whereas Structural-AKI was defined by elevations in urinary NGAL.

RESULTS

On ICU entry, the area under the curve (AUC) for the diagnosis of Functional-AKI was 0.74 (95% CI: 0.69-0.79), and for Structural-AKI it was 0.79 (0.74-0.83). Plasma NGAL also predicted the need for dialysis (0.79; 0.66-0.81), but not for death. A principal component analysis demonstrated that the maximum plasma NGAL in 24 h reflected structural injury marginally more than functional changes. Plasma NGAL added value to an AKI diagnostic model comprising plasma creatinine, sepsis, age, and APACHE II score (integrated discrimination improvement: 0.073; 0.034-0.12).

CONCLUSION

Increased plasma NGAL reflects both decreased filtration and structural injury. For patients at a low calculated risk, the addition of NGAL reduced the risk, and for those at a higher risk, NGAL correctly assigned patients to even a higher risk.

Clinical review: Predictive value of neutrophil gelatinase-associated lipocalin for acute kidney injury in intensive care patients

Neutrophil gelatinase-associated lipocalin (NGAL) may be an early marker of acute kidney injury (AKI), but elevated NGAL occurs in a wide range of systemic diseases. Because intensive care patients have high levels of comorbidity, our objective was to conduct a systematic review of the literature to evaluate the value of plasma and urinary NGAL to predict AKI in these patients. We conducted a systematic electronic literature search of MEDLINE through PubMed, EMBASE, and Cochrane Library for all English language research publications evaluating the predictive value of plasma or urinary NGAL (or both) for AKI in adult intensive care patients. Two authors independently extracted data by using a standardized extraction sheet including study characteristics, type of NGAL measurements, and type of outcome measures. The primary summary measure was area under receiver operating characteristic curve (AuROC) for NGAL to predict study outcomes. Eleven studies with a total of 2,875 (range of 20 to 632) participants were included: seven studies assessed urinary NGAL and six assessed plasma NGAL. The included studies varied in design, including observation period from NGAL sampling to AKI follow-up (range of 12 hours to 7 days), definition of baseline creatinine value, and urinary NGAL quantification method (normalizing to urinary creatinine or absolute concentration). AuROC values for the prediction of AKI ranged from 0.54 to 0.98. Five studies reported AuROC for use of renal replacement therapy ranging from 0.73 to 0.89, and four studies reported AuROC for mortality ranging from 0.58 to 0.83. There were no differences in the predictive values of urinary and plasma NGAL. The heterogeneity in study design and results made it difficult to evaluate the value of NGAL to predict AKI in intensive care patients. NGAL seems to have reasonable value in predicting use of renal replacement therapy but not mortality.

Novel biomarkers of acute kidney injury in the general adult ICU: a review

Acute kidney injury is one of the most frequent problems occurring in the critically ill patients of the intensive care units and it is well established that it increases both morbidity and mortality in these patients. Moreover, despite technological and pharmaceutical advances during the last decades, the incidence as well as the mortality associated with acute kidney injury in these patients remains unchanged. Creatinine, the most common renal dysfunction biomarker in use, has many disadvantages, such as time delay in its increase and the influence by other factors on its serum concentration, such as age, gender, muscle mass, etc. Hence, the need for better renal biomarkers in order to timely intervene for acute kidney injury prevention is imperative. The lack of an early biomarker is an obstacle for the development of new acute kidney injury prevention strategies. With the incidence of acute kidney injury reaching epidemic dimensions, the need for novel markers is urgent. During the last years, the research for finding such biomarkers has been intense. The purpose of the present article is to review the studies which have tested the predictive ability of those markers (in urine and/or plasma) for early detection of acute kidney injury in the mixed adult intensive care unit population and underline the potential limitations encountered in the various studies.

[Plasma Neutrophil Gelatinase-Associated Lipocalin (NGAL) predicts acute kidney injury in septic shock at ICU admission]

PURPOSE

To validate plasma Neutrophil Gelatinase-Associated Lipocalin (pNGAL) as an early biomarker in intensive care unit (ICU) for acute kidney injury (AKI) in critically ill adult with septic shock.

PATIENTS AND METHOD

Fifty consecutive patients with septic shock were included in this observational cohort study. AKI was defined if patients met any RIFLE or AKIN criteria. The main objective was to evaluate diagnosis value of pNGAL measured with a point-of-care device at admission (D0), at 24hours (D1) and at 48hours (D2).

RESULTS

Among the 50 patients enrolled, 86% had AKI, 48% had persistent renal AKI and 30% required renal replacement therapy (RRT) during their ICU stay. At D0, pNGAL concentration was significantly higher in patients with AKI compared to patients without AKI (471ng/mL versus 134ng/mL, P<0.001). This level remained significantly higher in the AKI population at D1 and D2 and pNGAL concentration at D0 among AKI patients increased with kidney failure level. At D1, pNGAL was significantly higher for persistent renal AKI rather than transient prerenal (570ng/mL versus 337ng/mL, P=0.027). pNGAL concentration below 348ng/mL at D1 was never seen in patients with RRT.

CONCLUSION

Plasma NGAL is a useful, sensitive and early biomarker to predict persistent AKI in septic shock at ICU admission and help to discuss RRT.

Role of new biomarkers: functional and structural damage

Traditional diagnosis of acute kidney injury (AKI) depends on detection of oliguria and rise of serum creatinine level, which is an unreliable and delayed marker of kidney damage. Delayed diagnosis of AKI in the critically ill patient is related to increased morbidity and mortality, prolonged length of stay, and cost escalation. The discovery of a reliable biomarker for early diagnosis of AKI would be very helpful in facilitating early intervention, evaluating the effectiveness of therapy, and eventually reducing cost and improving outcome. Innovative technologies such as genomics and proteomics have contributed to the discovery of new biomarkers, such as neutrophil gelatinase-associated lipocalin (NGAL), cystatin C (Cys C), kidney injury molecule-1 (KIM-1), interleukin-18 (IL-18), and liver-type fatty acid binding protein (L-FABP). The current status of the most promising of these novel AKI biomarkers, including NGAL, Cys C, KIM-1, L-FABP, and IL-18, is reviewed.

Accuracy of plasma neutrophil gelatinase-associated lipocalin in the early diagnosis of contrast-induced acute kidney injury in critical illness

PURPOSE

Neutrophil gelatinase-associated lipocalin (NGAL) is a promising biomarker for acute kidney injury (AKI). We evaluated the diagnostic and prognostic accuracies of plasma NGAL (pNGAL) for contrast-induced AKI (CI-AKI) in critically ill patients.

METHODS

In a prospective observational study in two adult intensive care units in a university hospital, 100 consecutive critically ill patients with stable serum creatinine concentrations up to 48 h before contrast medium (CM) injection were enrolled. Serial blood sampling for pNGAL analysis was performed at enrolment, 2, 6, and 24 h after CM injection. The primary outcome was CI-AKI, defined by AKIN criteria, within the first 72 h following CM injection. Secondary outcomes were the need for renal replacement therapy (RRT) and mortality.

RESULTS

Of the 98 patients analyzed, 30 developed CI-AKI. The pNGAL levels did not differ in patients with or without CI-AKI, and were higher in septic patients compared to nonseptic patients, and in patients with AKI preceding CM injection. The discriminative value of pNGAL to predict CI-AKI and mortality was poor; although, it did predict the need for RRT requirement after CM injection (area under receiver-operating characteristic curve, 0.85, 0.80, 0.83 and 0.86 at H0, H2, H6 and H24, respectively).

CONCLUSION

CI-AKI was common in critically ill patients. pNGAL levels were higher in patients with sepsis or previous AKI, but did not help to diagnose CI-AKI any earlier than serum creatinine after CM injection. However, pNGAL could be of interest to detect patients at risk of subsequent RRT requirement.

New biomarkers for the quick detection of acute kidney injury

Acute kidney injury (AKI) is a common and strong problem in the diagnosis of which based on measurement of BUN and serum creatinine. These traditional methods are not sensitive and specific for the diagnosis of AKI. AKI is associated with increased morbidity and mortality in critically ill patients and a quick detection is impossible with BUN and serum creatinine. A number of serum and urinary proteins have been identified that may messenger AKI prior to a rise in BUN and serum creatinine. New biomarkers of AKI, including NGAL, KIM-1, cystatin-C, IL-18, and L-FABP, are more favourable tests than creatinine which have been identified and studied in several experimental and clinical training. This paper will discuss some of these new biomarkers and their potential as useful signs of AKI. We searched the literature using PubMed and MEDLINE with acute kidney injury, urine, and serum new biomarkers and the articles were selected only from publication types in English.

Urinary and serum biomarkers for the diagnosis of acute kidney injury: an in-depth review of the literature

BACKGROUND

Acute kidney injury (AKI) remains associated with high morbidity and mortality, despite progress in medical care. Although the RIFLE (Risk, Injury, Failure, Loss, End-Stage Kidney Disease) and AKIN (Acute Kidney Injury Network) criteria, based on serum creatinine and urine output, were a step forward in diagnosing AKI, a reliable tool to differentiate between true parenchymal and pre-renal azotaemia in clinical practice is still lacking. In the last decade, many papers on the use of new urinary and serum biomarkers for the diagnosis and prognostication of AKI have been published. Thus, the question arises which biomarker is a reliable differential diagnostic tool under which circumstances.

METHODS

We searched Medline from inception to April 2012 using medical subject heading and text words for AKI and biomarkers [neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), Cystatin C, interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-18 (IL-18), N-acetyl-glucosaminidase (NAG), glutathione transferases (GST) and liver fatty acid binding protein (LFABP)] to identify relevant papers in five different settings (paediatrics, cardiac surgery, emergency department, critically ill and contrast-induced nephropathy).

RESULTS

We included 87 relevant papers, reporting on 74 studies. Depending upon the setting, 7-27 different definitions of AKI were used. Reported diagnostic performance of the different biomarkers was variable from poor to excellent, and no consistent generalizable conclusions can be drawn on their diagnostic value.

CONCLUSIONS

Early diagnosing of AKI in clinical conditions by using new serum and urinary biomarkers remains cumbersome, especially in those settings where timing and aetiology of AKI are not well defined. Putting too much emphasis on markers that have not convincingly proven reliability might lead to incorrect interpretation of clinical trials. Further research in this field is warranted before biomarkers can be introduced in clinical practice.

Systemic and urinary neutrophil gelatinase-associated lipocalins are poor predictors of acute kidney injury in unselected critically ill patients

Background. Neutrophil gelatinase-associated lipocalin (NGAL) in serum and urine have been suggested as potential early predictive biological markers of acute kidney injury (AKI) in selected critically ill patients. Methods. We performed a secondary analysis of a multicenter prospective observational cohort study of unselected critically ill patients. Results. The analysis included 140 patients, including 57 patients who did not develop AKI, 31 patients who developed AKI, and 52 patients with AKI on admission to the ICU. Levels of sNGAL and uNGAL on non-AKI days were significantly lower compared to levels of sNGAL on RIFLE_RISK days, RIFLE_INJURY days, and RIFLE_FAILURE days. The AUC of sNGAL for predicting AKI was low: 0.45 (95% confidence interval (CI) 0.27–0.63) and 0.53 (CI 0.38–0.67), 2 days and 1 day before development of AKI, respectively. The AUC of uNGAL for predicting AKI was also low: 0.48 (CI 0.33–0.62) and 0.48 (CI 0.33–0.62), 2 days and 1 day before development of AKI, respectively. AUC of sNGAL and uNGAL for the prediction of renal replacement therapy requirement was 0.47 (CI 0.37–0.58) and 0.26 (CI 0.03–0.50). Conclusions. In unselected critically ill patients, sNGAL and uNGAL are poor predictors of AKI or RRT.

A comparison of RIFLE with and without urine output criteria for acute kidney injury in critically ill patients

Introduction

The Risk, Injury, Failure, Loss, and End-Stage Renal Disease (RIFLE) is a consensus-based classification system for diagnosing acute kidney insufficiency (AKI), based on serum creatinine (SCr) and urine output criteria (RIFLE_SCr+UO). The urine output criteria, however, are frequently discarded and many studies in the literature applied only the SCr criteria (RIFLE_SCr). We diagnosed AKI using both RIFLE methods and compared the effects on time to AKI diagnosis, AKI incidence and AKI severity.

Methods

This was a prospective observational cohort study during four months in adult critically ill patients admitted to the ICU for at least 48 hours. During the first week patients were scored daily for AKI according to RIFLE_SCr+UO and RIFLE_SCr. We assessed urine output hourly and fluid balance daily. The baseline SCr was estimated if a recent pre-ICU admission SCr was unknown. Based on the two RIFLE methods for each patient we determined time to AKI diagnosis (AKI-0) and maximum RIFLE grade.

Results

We studied 260 patients. A pre-ICU admission SCr was available in 101 (39%) patients. The two RIFLE methods resulted in statistically significantly different outcomes for incidence of AKI, diagnosis of AKI for individual patients, distribution of AKI-0 and distribution of the maximum RIFLE grade. Discarding the RIFLE urine criteria for AKI diagnosis significantly underestimated the presence and grade of AKI on admission and during the first ICU week (P < 0,001) and significantly delayed the diagnosis of AKI (P < 0.001). Based on RIFLE_SCr 45 patients had no AKI on admission but subsequently developed AKI. In 24 of these patients (53%) AKI would have been diagnosed at least one day earlier if the RIFLE urine criteria had been applied. Mortality rate in the AKI population was 38% based on RIFLE_SCr and 24% based on RIFLE_SCr+UO (P = 0.02).

Conclusions

The use of RIFLE without the urine criteria significantly underscores the incidence and grade of AKI, significantly delays the diagnosis of AKI and is associated with higher mortality.

Clinical review: Biomarkers of acute kidney injury: where are we now?

The recognition that acute kidney injury (AKI) is a significant independent risk factor for morbidity and mortality has resulted in a substantial number of publications over the past 5 years or more. In no small part these have, to a degree, highlighted the inadequacy of conventional markers of renal insufficiency in the acute setting. Much effort has been invested in the identification of early, specific AKI markers in order to aid early diagnosis of AKI and hopefully improve outcome. The search for a 'biomarker' of AKI has seen early promise replaced by a degree of pessimism due to the lack of a clear candidate molecule and variability of results. We outline the major studies described to date as well as discuss potential reasons for the discrepancies observed and suggest that evolution of the field may result in success with ultimately an improvement in patient outcomes.

Combination of renal biomarkers predicts acute kidney injury in critically ill adults

OBJECTIVE

Most studies so far have focused on the performance of individual biomarkers to detect early acute kidney injury (AKI) in the adult intensive care unit (ICU) patients; however, they have not determined the predictive ability of their combinations. The aim of this study was to compare the predictive abilities of plasma neutrophil gelatinase-associated lipocalin (pNGAL), urine neutrophil gelatinase-associated lipocalin (uNGAL), plasma cystatin C (pCysC), serum creatinine (sCr), and their combinations in detecting AKI in an adult general ICU population.

METHODS

A total of 100 consecutive ICU patients were included in the analysis. AKI was defined according to RIFLE criteria. Biomarker predictive abilities were evaluated by area under the curve (AUC), net reclassification improvement (NRI), and integrated discrimination improvement (IDI).

RESULTS

AKI occurred in 36% of patients 7 days post-admission. All three novel biomarkers as well as sCr had moderate predictive abilities for AKI occurrence. The most efficient combinations (pNGAL + sCr and pNGAL + uNGAL + sCr) were selected to participate in the subsequent analyses. Both combinations, when added to a reference clinical model, increased its AUC significantly (0.858, p = 0.04). Their NRI (0.78, p = 0.0002) was equal to that of pNGAL, but higher than that of the other three biomarkers, whereas their IDI was higher than that of any individual biomarker (0.23, p = 0.0001). Both combinations had better specificities, positive likelihood ratios, and positive predictive values than those of any individual biomarker.

CONCLUSION

The biomarker combinations had better predictive characteristics compared with those of each biomarker alone.

Progressive Increase of Inflammatory Biomarkers in Chronic Kidney Disease and End-Stage Renal Disease

Chronic kidney disease (CKD) has reached epidemic levels. It is a multisystem disease associated with elevated systemic inflammatory and hypercoagulable states. Most concerning are the cardiovascular risks associated with all stages of kidney disease. It is difficult to assess kidney disease stage progression and cardiovascular risk with current indicators such as estimated glomerular filtration rate and conventional cardiovascular risk factors. However, the use of biomarkers to assess the underlying pathological disease state may bridge the gap. This study evaluated biomarkers of inflammation including C-reactive protein, d-dimer, neuron-specific enolase, neutrophil gelatinase–associated lipocalin, tumor necrosis factor receptor I, and thrombomodulin in 3 groups of patients: CKD stages 2-4, end-stage renal disease (ESRD), and age-matched controls. The study demonstrated a statistically significant progressive upregulation in mean concentration of all markers when comparing controls to CKD and ESRD. Therefore, biomarkers may be able to evaluate the inflammatory state in kidney disease and potentially predict the cardiovascular risk.

[NGAL, biomarker of acute kidney injury in 2012]

Neutrophil Gelatinase Associated Lipocalin (NGAL) is one of the most promising biomarkers for acute kidney injury (AKI). Although urinary NGAL is intuitively more appropriate to apprehend renal injury, clinical data have accumulated on the potential interest of NGAL measured indifferently in serum or urine. Diagnostic performance of NGAL greatly varies across studies according to different factors such as the type of patients (pediatric versus adult) and the clinical situations (surgery versus intensive care). Overall, NGAL is presented as a useful tool to diagnose and predict AKI outcome but several issues (the absence of a unique pertinent threshold value, the incomplete analytical validation of its measurement and, its apparent limited clinical added value as compared to traditional AKI markers) remain to be addressed in order to definitely recommend its use in clinical practice.

Marking renal injury: can we move beyond serum creatinine?

Acute kidney injury (AKI) is a prevalent and devastating condition associated with significant morbidity and mortality. Despite marked improvements in clinical care, the outcomes for subjects with AKI have shown limited improvement in the past 50 years. A major factor inhibiting clinical progress in this field has been the inability to accurately predict and diagnose early kidney dysfunction. The current gold standard clinical and biochemical criteria for diagnosis of AKI, Risk Injury Failure Loss End-stage renal disease, and its modification, Acute Kidney Injury Network criteria, rely on urine output and serum creatinine, which are insensitive, nonspecific, and late markers of disease. The recent development of a variety of analytic mass spectrometry-based platforms have enabled separation, characterization, detection, and quantification of proteins (proteomics) and metabolites (metabolomics). These high-throughput platforms have raised hopes of identifying novel protein and metabolite markers, and recent efforts have led to several promising novel markers of AKI. However, substantial challenges remain, including the need to systematically evaluate incremental performance of these markers over and beyond current clinical and biochemical criteria for AKI. We discuss the basic issues surrounding AKI biomarker development, highlight the most promising markers currently under development, and discuss the barriers toward widespread clinical implementation of these markers.

Neutrophil Gelatinase-Associated Lipocalin (NGAL) predicts renal injury in acute decompensated cardiac failure: a prospective observational study

Background

Acute Decompensated Cardiac Failure (ADCF) is frequently associated with deterioration in renal function. Neutrophil gelatinase-associated lipocalin (NGAL) is an early marker of kidney injury. We aimed to determine if NGAL measured at admission predicts in-hospital acute kidney injury (AKI) in ADCF.

Methods

A prospective observational study measured NGAL and B-natriuretic peptide (BNP) from patients with ADCF presenting to two tertiary hospitals. Patients received standard care and were followed up daily as inpatients. ADCF was defined by PRIDE score ≥ 6 and AKI by RIFLE criteria.

Results

One hundred and two patients (median age 80, IQR 69-84 years, 52% male) were enrolled. AKI developed in 22 (25%) of 90 for whom outcome data was available. Seven patients died. NGAL was significantly elevated in those who developed AKI versus those who did not (median 130 ng/ml vs 69 ng/ml, p = 0.002). NGAL was also higher in those who died (median 136 ng/ml vs 68 ng/ml, p = 0.005). AKI was significantly associated with risk of death (5/22 (23%) vs 1/68 (1.5%), p = 0.001), but not length of hospital stay. NGAL significantly correlated with admission eGFR but not BNP. For prediction of AKI, NGAL > 89 ng/ml had sensitivity of 68% and specificity of 70% with area under the receiver operator characteristic (ROC) curve of 0.71 (0.58-0.84). After adjustment for baseline renal function, the odds ratio (OR) for AKI was 3.73 (1.26-11.01) if admission NGAL > 89 ng/ml.

Conclusions

Elevated NGAL at admission is associated with in-hospital AKI and mortality in patients with ADCF. However, it has only moderate diagnostic accuracy in this setting.

Cardio-renal syndrome: new perspective in diagnostics

Chronic heart failure and chronic renal failure are at epidemic proportions. These patients have significantly altered cardiac, renal, and all-cause outcomes. Much of the current research has focused on treating these individual organs in isolation. Although there are positive data on outcomes with neurohormonal modulation, they, however, remain underused. At present, data lacks for novel treatment options, while evidence continues to point at significantly worsened prognosis. Current diagnostic tools that detect acute changes in renal function or renal injury appear retrospective, which often hinder meaningful diagnostic and therapeutic decisions. This review is aimed at exploring the importance of accurate assessment of renal function for the heart failure patient by providing a synopsis on cardio-renal physiology and establishing the possibility of novel approaches in bridging the divide.

Neutrophil Gelatinase Associated Lipocalin: An Emerging Biomarker for Acute Kidney Injury in Cardiovascular Disease

Acute kidney injury (AKI) commonly occurs in hospitalised patients resulting in short and long-term morbidity and mortality. A subset of patients especially those with cardiovascular diseases appear particularly vulnerable. The diagnosis of AKI currently depends on changes in serum creatinine and is usually made at least 24 to 48 hours after the initial renal insult. This hinders formulation of possible early therapeutic strategies which could otherwise reduce the clinical sequelae of AKI. Neutrophil gelatinase-associated lipocalin (NGAL) is released in both serum and urine, and has shown great promise in identifying AKI as early as two to four hours after renal injury. NGAL has been demonstrated to be both specific and sensitive in a variety of renal conditions associated with AKI, compared to serum creatinine. This article discusses the emerging role of NGAL in the diagnostic and prognostic evaluation of AKI secondary to cardiovascular diseases and interventions including its benefits and pitfalls. NGAL has been shown to be useful in the diagnosis of AKI particularly for contrast induced nephropathy (CIN) after percutaneous coronary intervention (PCI) and renal dysfunction complicating acute and chronic heart failure. Larger prospective outcome studies with therapeutic interventions are warranted to further validate the role of NGAL in the diagnosis of AKI and in cardiorenal syndrome.

Biomarkers of acute kidney injury

Acute kidney injury (AKI) is a common problem in both the inpatient and outpatient setting and often results from drug toxicities. Traditional methods of identifying AKI, through measurement of blood urea nitrogen and serum creatinine, are problematic in that they are slow to detect decreases in glomerular filtration rate (GFR) and are influenced by a variety of factors that are not related to GFR changes. The problems inherent in a creatinine-based diagnosis of AKI have impeded the development of proper therapeutics in AKI and posed problems in evaluating nephrotoxicity of drugs and other chemical exposures. In recent years, a number of new biomarkers of AKI with more favorable test characteristics than creatinine have been identified and studied in a variety of experimental and clinical settings. This review will consider the most well-established biomarkers and appraise the literature, with particular attention given to the use of biomarkers in identifying toxin-mediated AKI.

Biomarker strategies to predict need for renal replacement therapy in acute kidney injury

The early detection and diagnosis of acute kidney injury (AKI) with the standardization of novel kidney-injury-specific biomarkers is one of the highest research priorities in nephrology. Accordingly, the majority of studies of novel AKI biomarkers have focused on the early diagnosis of AKI using serum creatinine-based definitions as the gold standard. However, another potential application of kidney-injury-specific biomarkers is for guiding decisions on when to initiate renal replacement therapy (RRT). The purpose of this review is to summarize recent findings concerning some of the more promising AKI biomarkers on their capacity, either alone or integrated with traditional surrogate measures of kidney injury, for early prediction of whether patients will develop severe AKI requiring RRT. Some studies that have examined neutrophil gelatinase-associated lipocalin, cystatin-C, N-acetyl-β-d-glucosaminidase, kidney injury molecule-1, and α(1)-microglobulin, among others, have suggested that these novel biomarkers have the potential to distinguish patients in whom RRT will be needed. This would imply that these biomarkers may be integrated into clinical decision algorithms and could synergistically improve our current ability to predict worsening AKI and need for RRT. However, published studies have many recognized limitations, which preclude our ability to adapt their findings into clinical practice today. While currently available data are not sufficient to conclude that biomarkers should be used routinely for clinical decision making for RRT initiation, additional data may in the future significantly modify the clinical variability for initiation of RRT, and potentially translate into improved outcomes and cost-effectiveness. Finally, we propose a potential approach to future biomarker strategies for RRT initiation, integrating these biomarkers with "traditional" clinical factors.

Urinary Neutrophil Gelatinase-Associated Lipocalin Measured on Admission to the Intensive Care Unit Accurately Discriminates between Sustained and Transient Acute Kidney Injury in Adult Critically Ill Patients

Background

First we aimed to evaluate the ability of neutrophil gelatinase-associated lipocalin (NGAL) and cystatin-C (CyC) in plasma and urine to discriminate between sustained, transient and absent acute kidney injury (AKI), and second to evaluate their predictive performance for sustained AKI in adult intensive care unit (ICU) patients.

Methods

A prospective cohort study of 700 patients was studied. Sample collection was performed over 8 time points starting on admission.

Results

After exclusion 510 patients remained for the analysis. All biomarkers showed significant differentiation between sustained and no AKI at all time points (p ≤ 0.0002) except for urine CyC (uCyC) on admission (p = 0.06). Urine NGAL (uNGAL) was the only biomarker significantly differentiating sustained from transient AKI on ICU admission (p = 0.02). Individually, uNGAL performed better than the other biomarkers (area under the curves, AUC = 0.80, 95% confidence interval, CI = 0.72–0.88) for the prediction of sustained AKI. The combination with plasma NGAL (pNGAL) showed a nonsignificant improvement (AUC = 0.83, 95% CI = 0.75–0.91). The combination of individual markers with a model of clinical characteristics (MDRD eGFR, HCO₃⁻ and sepsis) did not improve its performance significantly. However, the integrated discrimination improvement showed significant improvement when uNGAL was added (p = 0.04).

Conclusions

uNGAL measured on ICU admission differentiates patients with sustained AKI from transient or no-AKI patients. Combining biomarkers such as pNGAL, uNGAL and plasma CyC with clinical characteristics adds some value to the predictive model.

Biomarkers in chronic kidney disease: a review

Chronic kidney disease (CKD) is a major public health problem. The classification of CKD by KDOQI and KDIGO and the routine eGFR reporting have resulted in increased identification of CKD. It is important to be able to identify those at high risk of CKD progression and its associated cardiovascular disease (CVD). Proteinuria is the most sensitive marker of CKD progression in clinical practice, especially when combined with eGFR, but these have limitations. Hence, early, more sensitive, biomarkers are required. Recently, promising biomarkers have been identified for CKD progression and its associated CVD morbidity and mortality. These may be more sensitive biomarkers of kidney function, the underlying pathophysiological processes, and/or cardiovascular risk. Although there are some common pathways to CKD progression, there are many primary causes, each with its own specific pathophysiological mechanism. Hence, a panel measuring multiple biomarkers including disease-specific biomarkers may be required. Large, longitudinal observational studies are needed to validate candidate biomarkers in a broad range of populations prior to implementation into routine CKD management. Recent renal biomarkers discovered include neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, and liver-type fatty acid-binding protein. Although none are ready for use in clinical practice, it is timely to review the role of such biomarkers in predicting CKD progression and/or CVD risk in CKD.

Plasma neutrophil gelatinase-associated lipocalin predicts recovery from acute kidney injury following community-acquired pneumonia

Although plasma neutrophil gelatinase-associated lipocalin (NGAL) is a promising biomarker for early detection of acute kidney injury, its ability to predict recovery is unknown. Using RIFLE criteria to define kidney injury, we tested whether higher plasma NGAL concentrations on the first day of RIFLE-F would predict failure to recover in a post hoc analysis of a multicenter, prospective, cohort study of patients with community-acquired pneumonia. Recovery was defined as alive and not requiring renal replacement therapy during hospitalization or having a persistent RIFLE-F classification at hospital discharge. Median plasma NGAL concentrations were significantly lower among the 93 of 181 patients who recovered. Plasma NGAL alone predicted failure to recover with an area under the receiver operating characteristic curve of 0.74. A clinical model using age, serum creatinine, pneumonia severity, and nonrenal organ failure predicted failure to recover with area under the curve of 0.78. Combining this clinical model with plasma NGAL concentrations did not improve prediction. The reclassification of risk of renal recovery, however, significantly improved by 17% when plasma NGAL was combined with the clinical model. Thus, in this cohort of patients with pneumonia-induced severe acute kidney injury, plasma NGAL appears to be a useful biomarker for predicting renal recovery.

A comparison of alternative serum biomarkers with creatinine for predicting allograft function after kidney transplantation

BACKGROUND

The role of serum cystatin C (Scyc), neutrophil gelatinase-associated lipocalin, and interleukin-18 in predicting early graft function after kidney transplant is poorly defined.

METHODS

We conducted a multicenter prospective cohort study of deceased-donor kidney transplants. We collected serial blood samples for the first 3 days of transplant and monitored need for dialysis within 1 week and graft function at 3 months after transplant.

RESULTS

Among 78 recipients with serum biomarker measurements, 26 had delayed graft function (DGF; hemodialysis within 1 week of transplant). Of those not dialyzed, 29 had slow graft function (serum creatinine [Scr] reduction from transplantation to day 7 <70%), and 23 had immediate graft function (IGF; reduction in Scr ≥70%). Scyc levels were statistically different between groups by the first postoperative day (POD), whereas Scr levels were not. Serum neutrophil gelatinase-associated lipocalin and serum interleukin-18 levels were not different between groups. Scyc on the first POD demonstrated good utility for predicting DGF and non-IGF (DGF or slow graft function) with areas under the receiver-operating characteristic curve of 0.83 and 0.85, respectively. Areas under the receiver-operating characteristic curve for predicting DGF and non-IGF using Scr on the first POD were 0.65 and 0.53, respectively. Substituting Scyc for Scr in a clinical algorithm improved its utility for predicting DGF or non-IGF, with adjusted odds ratios of 2.4 and 3.3 for Scyc levels on the first POD. The change in Scyc during the first POD demonstrated a dose-response relationship with 3-month graft function.

CONCLUSIONS

Scyc outperforms Scr as a predictor of early graft function after deceased-donor kidney transplant.

Biomarkers for the early detection of acute kidney injury

PURPOSE OF REVIEW

Acute kidney injury (AKI) is a common and serious condition, the diagnosis of which depends on serum creatinine, which is a delayed and unreliable indicator of AKI. Fortunately, understanding the early stress response of the kidney to acute injuries has revealed a number of potential biomarkers. The current status of the most promising of these novel AKI biomarkers, including neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), liver-type fatty acid binding protein (L-FABP), and interleukin (IL)-18, is reviewed.

RECENT FINDINGS

In particular, NGAL is emerging as an excellent biomarker in the urine and plasma, for the early prediction of AKI, for monitoring clinical trials in AKI, and for the prognosis of AKI in several common clinical scenarios. However, biomarker combinations may be required to improve our ability to predict AKI and its outcomes in a context-specific manner.

SUMMARY

It is vital that additional large future studies demonstrate the association between biomarkers and hard clinical outcomes independent of serum creatinine concentrations and that randomization to a treatment for AKI based on high biomarker levels results in an improvement in clinical outcomes.

Evolving use of biomarkers for kidney injury in acute care settings

PURPOSE OF REVIEW

Acute kidney injury is increasingly recognized in acute care settings in more recent years. Proper diagnosis and risk stratification for acute kidney injury is necessary for carrying out appropriate and cost-effective treatments in patients with acute kidney injury. Kidney markers serve as diagnostic and prognostic tools to give physicians a more complete perspective of renal insult. The aim of this review is to highlight some of the evidence from recent studies, involving kidney markers and provide current opinion on the accuracy of these markers.

RECENT FINDINGS

Recent studies demonstrate that novel kidney markers such as cystatin C, interleukin-18, kidney injury molecule 1, and neutrophil gelatinase-associated lipocalin serve as more accurate markers for acute kidney injury as compared with the more traditional marker, creatinine. Additionally, there seems to be a correlation between the concentrations of each marker and the level of deterioration of kidneys, patient recovery time, length of hospital stay, and hospital costs.

SUMMARY

Each individual kidney marker possesses its own strengths and weaknesses in determining the onset and severity of acute kidney injury. However, in combination, a panel of kidney markers may serve as powerful tools in diagnosing kidney injury with high accuracy.

Review: neutrophil gelatinase-associated lipocalin: a troponin-like biomarker for human acute kidney injury

Acute kidney injury (AKI) is a common and serious condition, the diagnosis of which currently depends on functional markers such as serum creatinine measurements. Unfortunately, creatinine is a delayed and unreliable indicator of AKI. The lack of early biomarkers of structural kidney injury (akin to troponin in acute myocardial injury) has hampered our ability to translate promising experimental therapies to human AKI. Fortunately, understanding the early stress response of the kidney to acute injuries has revealed a number of potential biomarkers. The discovery, translation and validation of neutrophil gelatinase-associated lipocalin (NGAL), possibly the most promising novel AKI biomarker, is reviewed. NGAL is emerging as an excellent stand-alone troponin-like structural biomarker in the plasma and urine for the early diagnosis of AKI, and for the prediction of clinical outcomes such as dialysis requirement and mortality in several common clinical scenarios. The approach of using NGAL as a trigger to initiate and monitor therapies for AKI, and as a safety biomarker when using potentially nephrotoxic agents, is also promising. In addition, it is hoped that the use of sensitive and specific biomarkers such as NGAL as endpoints in clinical trials will result in a reduction in required sample sizes, and hence the cost incurred. Furthermore, predictive biomarkers like NGAL may play a critical role in expediting the drug development process. However, given the complexity of AKI, additional biomarkers (perhaps a panel of plasma and urinary biomarkers) may eventually need to be developed and validated for optimal progress to occur.

Neutrophil gelatinase-associated lipocalin at ICU admission predicts for acute kidney injury in adult patients

RATIONALE

Measured at intensive care unit admission (ICU), the predictive value of neutrophil gelatinase-associated lipocalin (NGAL) for severe acute kidney injury (AKI) is unclear.

OBJECTIVES

To assess the ability of plasma and urine NGAL to predict severe AKI in adult critically ill patients.

METHODS

Prospective-cohort study consisting of 632 consecutive patients.

MEASUREMENTS AND MAIN RESULTS

Samples were analyzed by Triage immunoassay for NGAL expression. The primary outcome measure was occurrence of AKI based on Risk-Injury-Failure (RIFLE) classification during the first week of ICU stay. A total of 171 (27%) patients developed AKI. Of these 67, 48, and 56 were classified as RIFLE R, I, and F, respectively. Plasma and urine NGAL values at ICU admission were significantly related to AKI severity. The areas under the receiver operating characteristic curves for plasma and urine NGAL were for RIFLE R (0.77 ± 0.05 and 0.80 ± 0.04, respectively), RIFLE I (0.80 ± 0.06 and 0.85 ± 0.04, respectively), and RIFLE F (0.86 ± 0.06 and 0.88 ± 0.04, respectively) and comparable with those of admission estimated glomerular filtration rate (eGFR) (0.84 ± 0.04, 0.87 ± 0.04, and 0.92 ± 0.04, respectively). Plasma and urine NGAL significantly contributed to the accuracy of the "most efficient clinical model" with the best four variables including eGFR, improving the area under the curve for RIFLE F prediction to 0.96 ± 0.02 and 0.95 ± 0.01. Serial NGAL measurements did not provide additional information for the prediction of RIFLE F.

CONCLUSIONS

NGAL measured at ICU admission predicts the development of severe AKI similarly to serum creatinine-derived eGFR. However, NGAL adds significant accuracy to this prediction in combination with eGFR alone or with other clinical parameters and has an interesting predictive value in patients with normal serum creatinine.

Neutrophil gelatinase-associated lipocalin: a promising biomarker for human acute kidney injury

Acute kidney injury (AKI) is a common and serious condition, the diagnosis of which depends on serum creatinine measurements. Unfortunately, creatinine is a delayed and unreliable indicator of AKI. The lack of early biomarkers has crippled our ability to translate promising experimental therapies to human AKI. Fortunately, understanding the early stress response of the kidney to acute injuries has revealed a number of potential biomarkers. The discovery, translation and validation of neutrophil gelatinase-associated lipocalin, arguably the most promising novel AKI biomarker, are reviewed in this article. Neutrophil gelatinase-associated lipocalin is emerging as an excellent standalone troponin-like biomarker in the plasma and urine for the prediction of AKI, monitoring clinical trials in AKI and for the prognosis of AKI in several common clinical scenarios.

Back-calculating baseline creatinine with MDRD misclassifies acute kidney injury in the intensive care unit

BACKGROUND AND OBJECTIVES

The purpose of this study was to assess the viability of back-calculation with the Modification of Diet in Renal Disease (MDRD) formula to determine baseline creatinine on the basis of acute kidney injury (AKI) metrics, RIFLE criteria, and Acute Kidney Injury Network (AKIN) criteria for the purpose of clinical trial outcomes or epidemiology.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study was a retrospective analysis of prospectively collected data from patients with measured baseline creatinines before entry to the intensive care unit (ICU). The AKI status was determined using five different baseline creatinines: the measured creatinine (the standard) and an estimated creatinine determined by back-calculation using MDRD assuming a GFR of 75 ml/min (epCr75), 100 ml/min (epCr100), randomly generating a value on a lognormal curve (epCrRnd), and choosing the lowest creatinine value within the first week in the ICU (epCrlow). A subgroup of patients without chronic kidney disease (CKD) was similarly analyzed.

RESULTS

Of 224 patients, 70 (31%) had AKI according to RIFLE and 93 (42%) according to AKIN. The epCr75 and epCr100 distributions greatly overestimated the proportion with AKI. The epCrlow overestimated AKI according to AKIN but correctly estimated AKI according to RIFLE. The mean of 1000 epCrRnd distributions correctly estimated AKI according to RIFLE and AKIN. Each estimated distribution performed better in the non-CKD population with the exception of epCrRnd. However, only the epCrlow distribution accurately determined the proportion with AKI.

CONCLUSIONS

A measured rather than estimated value should be used for baseline creatinine in trials or epidemiologic studies of AKI.