Evaluation of new acute kidney injury biomarkers in a mixed intensive care unit

Association of Urinary Neutrophil Gelatinase-Associated Lipocalin With Long-Term Renal Outcomes in ICU Survivors: A Retrospective Observational Cohort Study

BACKGROUND

Epidemiological studies recently suggested that acute kidney injury (AKI) in intensive care units (ICUs) increases the risk of chronic kidney disease development and progression. However, whether any AKI biomarker can predict long-term renal outcomes in ICU survivors remains unclear. This study was undertaken to elucidate the role of urinary biomarkers for long-term renal outcome prediction after ICU discharge.

METHODS

This retrospective observational study examined 495 adult patients who had been admitted to the ICU of the University of Tokyo Hospital. Major adverse kidney events (MAKE): death, incident end-stage renal disease (ESRD), and halving of estimated glomerular filtration rate (eGFR), at hospital discharge and long-term renal outcomes of 30% reduction of eGFR or incident ESRD were evaluated.

RESULTS

Among all the enrolled 495 patients, 393 patients were discharged from the hospital without MAKE. Data of eGFR up to two years after ICU discharge were available for 173 patients; 63 patients (36.4%) were positive for long-term renal outcomes. Step-wise logistic regression analysis demonstrated that male sex and urinary neutrophil gelatinase-associated lipocalin (NGAL) measured at ICU admission showed significant associations with long-term renal outcomes. Receiver operating characteristic curve analysis showed the area under the curve of 0.66 (95% confidence interval 0.57-0.74) for prediction of long-term renal outcome by urinary NGAL.

CONCLUSION

Urinary NGAL measured at ICU admission was significantly associated with long-term renal outcomes after hospital discharge in MAKE-free ICU survivors. Urinary NGAL measurements at ICU might be useful to identify a high risk population of kidney disease progression after intensive care.

Angiotensinogen as a biomarker of acute kidney injury

Early recognition of acute kidney injury (AKI) is critical to prevent its associated complications as well as its progression to long term adverse outcomes like chronic kidney disease. A growing body of evidence from both laboratory and clinical studies suggests that inflammation is a key factor contributing to the progression of AKI regardless of the initiating event. Biomarkers of inflammation are therefore of interest in the evaluation of AKI pathogenesis and prognosis. There is evidence that the renin angiotensin aldosterone system is activated in AKI, which leads to an increase in angiotensin II (Ang II) formation within the kidney. Ang II activates pro-inflammatory and pro-fibrotic pathways that likely contribute to the progression of AKI. Angiotensinogen is the parent polypeptide from which angiotensin peptides are formed and its stability in urine makes it a more convenient marker of renin angiotensin system activity than direct measurement of Ang II in urine specimens, which would provide more direct information. The potential utility of urinary angiotensinogen as a biomarker of AKI is discussed in light of emerging data showing a strong predictive value of AKI progression, particularly in the setting of decompensated heart failure. The prognostic significance of urinary angiotensinogen as an AKI biomarker strongly suggests a role for renin-angiotensin system activation in modulating the severity of AKI and its outcomes.

Biomarkers for Early Detection of Acute Kidney Injury

BACKGROUND

Acute kidney injury (AKI) is common in hospitalized patients and is associated with increased morbidity, mortality, and cost. Currently, AKI is diagnosed after symptoms manifest; available diagnostic tests (e.g., serum creatinine, urine microscopy, urine output) have limited ability to identify subclinical AKI. Because of the lack of treatment strategies, AKI typically is managed with supportive measures. However, strategies exist that may prevent renal insults in critically ill patients; therefore, early recognition of AKI is crucial for minimizing damage propagation.

CONTENT

Experimental and clinical studies have identified biomarkers that may facilitate earlier recognition of AKI or even identify patients at risk of AKI. Such biomarkers might aid in earlier implementation of preventive strategies to slow disease progression and potentially improve outcomes. This review describes some of the most promising novel biomarkers of AKI, including neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule 1 (KIM-1), interleukin 18 (lL-18), liver-type fatty-acid-binding protein (L-FABP), insulin-like-growth-factor-binding protein 7 (IGFBP7), and tissue inhibitor of metalloproteinase 2 (TIMP-2).

SUMMARY

We discuss biomarker test characteristics, their strengths and weaknesses, and future directions of their clinical implementation.

Heparin-binding protein as a biomarker of acute kidney injury in critical illness

BACKGROUND

There is no biomarker with high sensitivity and specificity for the development of acute kidney injury (AKI) in a mixed intensive care unit (ICU) population. Heparin-binding protein (HBP) is released from granulocytes and causes increased vascular permeability which plays a role in the development of AKI in sepsis and ischemia. The aim of this study was to investigate whether plasma levels of HBP on admission can predict the development of AKI in a mixed ICU population and in the subgroup with sepsis.

METHODS

Longitudinal observational study with plasma HBP levels from 245 patients taken on admission to ICU. Presence and severity of AKI was scored daily for 1 week.

RESULTS

Mean (95% CI) plasma concentrations of log HBP (ng/ml) in the groups developing different stages of AKI were: stage 0 (n = 175), 3.5 (3.4-3.7); stage 1 (n = 33), 3.7 (3.5-4.0), stage 2 (n = 20), 4.4 (3.5-4.8); and stage 3 (n = 17), 4.6 (3.8-5.2). HBP levels were significantly higher in patients developing AKI stage 3 (P < 0.01) compared to AKI stage 0 and 1. The area under the curve (AUC) for HBP to discriminate the group developing AKI stage 2-3 was 0.70 (CI: 0.58-0.82) and in the subgroup with severe sepsis 0.88 (CI: 0.77-0.99).

CONCLUSION

Heparin-binding protein levels on admission to ICU are associated with the development of severe kidney injury. The relationship between HBP and AKI needs to be further validated in larger studies.

Biomarkers of acute kidney injury: the pathway from discovery to clinical adoption

Acute kidney injury (AKI) is a common complication of critical illnesses and has a significant impact on outcomes, including mortality and morbidities. Unfortunately, apart from prophylactic measures, no effective treatment for this syndrome is known. Therefore, early recognition of AKI not only can provide better opportunities for preventive interventions, but also opens many gates for research and development of effective therapeutic options. Over the last few years, several new AKI biomarkers have been discovered and validated to improve early detection, differential diagnosis, and differentiation of patients into risk groups for progressive renal failure, need for renal replacement therapy (RRT), or death. These novel AKI biomarkers complement serum creatinine (SCr) and urine output, which are the standard diagnostic tools for AKI detection. In this article, we review the available literature on characteristics of promising AKI biomarkers that are currently the focus of preclinical and clinical investigations. These biomarkers include neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule 1 (KIM-1), liver-type fatty acid-binding protein, interleukin 18 (lL-18), insulin-like growth factor-binding protein 7, tissue inhibitor of metalloproteinase 2 (TIMP-2), calprotectin, urine angiotensinogen (AGT), and urine microRNA. We then describe the clinical performance of these biomarkers for diagnosis and prognostication. We also appraise each AKI biomarker's advantages and limitations as a tool for early AKI recognition and prediction of clinical outcomes after AKI. Finally, we review the current and future states of implementation of biomarkers in the clinical practice.

Clinical Usefulness of Urinary Liver Fatty Acid-Binding Protein Excretion for Predicting Acute Kidney Injury during the First 7 Days and the Short-Term Prognosis in Acute Heart Failure Patients with Non-Chronic Kidney Disease

Background

The clinical significance of urinary liver fatty acid-binding protein (u-LFABP) in acute heart failure (AHF) patients remains unclear.

Methods and Results

The u-LFABP levels on admission of 293 AHF patients were analyzed. The patients were divided into 2 groups according to the u-LFABP quartiles (Q1, Q2, and Q3 = low u-LFABP [L] group vs. Q4 = high u-LFABP [H] group). We evaluated the diagnostic and prognostic value of u-LFABP and compared the findings between the chronic kidney disease (CKD; n = 165) and non-CKD patients (n = 128). Acute kidney injury (AKI) during the first 7 days was evaluated based on the RIFLE criteria. In the non-CKD group, the number of AKI patients during the first 7 days was significantly greater in the H group (70.0%) than in the L group (45.6%). A multivariate logistic regression model indicated that the H group (odds ratio: 3.850, 95% confidence interval [CI] 1.128-13.140) was independently associated with AKI during the first 7 days. The sensitivity and specificity of u-LFABP for predicting AKI were 63.6 and 59.7% (area under the ROC curve 0.631) at 41.9 ng/mg × cre. A Cox regression model identified the H group (hazard ratio: 13.494, 95% CI 1.512-120.415) as an independent predictor of the 60-day mortality. A Kaplan-Meier curve, including all-cause death within 60 days, showed a significantly poorer survival rate in the H group than in the L group (p = 0.036).

Conclusions

The u-LFABP level is an effective biomarker for predicting AKI during the first 7 days of hospitalization and an adverse outcome in AHF patients with non-CKD.

Deletion of β1-integrin in collecting duct principal cells leads to tubular injury and renal medullary fibrosis

The renal collecting duct (CD) contains two major cell types, intercalated (ICs) and principal cells (PCs). A previous report showed that deletion of β1-integrin in the entire renal CD causes defective CD morphogenesis resulting in kidney dysfunction. However, subsequent deletion of β1-integrin specifically in ICs and PCs, respectively, did not cause any morphological defects in the CDs. The discrepancy between these studies prompts us to reinvestigate the role of β1-integrin in CD cells, specifically in the PCs. We conditionally deleted β1-integrin in mouse CD PCs using a specific aquaporin-2 (AQP2) promoter Cre-LoxP system. The resulting mutant mice, β-1^f/fAQP2-Cre+, had lower body weight, failed to thrive, and died around 8-12 wk. Their CD tubules were dilated, and some of them contained cellular debris. Increased apoptosis and proliferation of PCs were observed in the dilated CDs. Trichrome staining and electron microscopy revealed the presence of peritubular and interstitial fibrosis that is associated with increased production of extracellular matrix proteins including collagen type IV and fibronectin, as detected by immunoblotting. Further analysis revealed a significantly increased expression of transforming growth factor-β (TGF-β)-induced protein, fibronectin, and TGF-β receptor-1 mRNAs and concomitantly increased phosphorylation of SMAD-2 that indicates the activation of the TGF-β signaling pathway. Therefore, our data reveal that normal expression of β1-integrin in PCs is a critical determinant of CD structural and functional integrity and further support the previously reported critical role of β1-integrin in the development and/or maintenance of the CD structure and function.

Severe bilateral ischemic-reperfusion renal injury: hyperacute and acute changes in apparent diffusion coefficient, T1, and T2 mapping with immunohistochemical correlations

The aim of this study was to investigate the hyperacute and acute changes in apparent diffusion coefficient (ADC), T1, and T2 mapping in rat kidneys after severe bilateral renal ischemic-reperfusion injury (IRI). After baseline MRI, 24 Spraque-Dawley rats with renal IRI were divided equally as group 1 (post-IRI MRI at 6 hours, days 1, 3, and 7) and groups 2, 3, and 4 (post-IRI MRI at 6 hours; 6 hours and day 1; 6 hours, days 1 and 3, respectively), while six other rats without IRI (group 5) were used as sham control. ADC, T1, and T2 values of the cortex and outer and inner stripes of outer medulla (OSOM and ISOM), and immunohistochemical studies assessing monocyte chemoattractant protein-1 (MCP-1), CD68+ cells, tubular cast formation, and collagen deposition in three zones at different time points were evaluated. Significantly reduced ADCs in OSOM and ISOM are noninvasive biomarkers denoting hyperacute damages after IRI. Linear regression analysis revealed a significant inverse correlation between 6-hour/baseline ADC ratios and MCP-1 staining (P < 0.001, r² = 0.738). ADC, T1, and T2 values are useful for assessing variable IRI changes in different layers depending on underlying microstructural and histopathological changes at different time points.

Evaluation of clinically available renal biomarkers in critically ill adults: a prospective multicenter observational study

BACKGROUND

Although serum cystatin C (sCysC), urinary N-acetyl-β-D-glucosaminidase (uNAG), and urinary albumin/creatinine ratio (uACR) are clinically available, their optimal combination for acute kidney injury (AKI) detection and prognosis prediction remains unclear. We aimed to assess the discriminative abilities of these biomarkers and their possible combinations for AKI detection and intensive care unit (ICU) mortality prediction in critically ill adults.

METHODS

A multicenter, prospective observational study was conducted in mixed medical-surgical ICUs at three tertiary care hospitals. One thousand eighty-four adult critically ill patients admitted to the ICUs were studied. We assessed the use of individual biomarkers (sCysC, uNAG, and uACR) measured at ICU admission and their combinations with regard to AKI detection and prognosis prediction.

RESULTS

AUC-ROCs for sCysC, uNAG, and uACR were calculated for total AKI (0.738, 0.650, and 0.683, respectively), severe AKI (0.839, 0.706, and 0.771, respectively), and ICU mortality (0.727, 0.793, and 0.777, respectively). The panel of sCysC plus uNAG detected total and severe AKI with significantly higher accuracy than either individual biomarkers or the other two panels (uNAG plus uACR or sCysC plus uACR). For detecting total AKI, severe AKI, and ICU mortality at ICU admission, this panel yielded AUC-ROCs of 0.756, 0.863, and 0.811, respectively; positive predictive values of 0.71, 0.31, and 0.17, respectively; and negative predictive values of 0.81, 0.97, and 0.98, respectively. Moreover, this panel significantly contributed to the accuracy of the clinical models for AKI detection and ICU mortality prediction, as measured by the AUC-ROC, continuous net reclassification index, and incremental discrimination improvement index. The comparable performance of this panel was further confirmed with bootstrap internal validation.

CONCLUSIONS

The combination of a functional marker (sCysC) and a tubular damage marker (uNAG) revealed significantly superior discriminative performance for AKI detection and yielded additional prognostic information on ICU mortality.

Biomarkers in acute kidney injury - pathophysiological basis and clinical performance

Various biomarkers of acute kidney injury (AKI) have been discovered and characterized in the recent past. These molecules can be detected in urine or blood and signify structural damage to the kidney. Clinically, they are proposed as adjunct diagnostics to serum creatinine and urinary output to improve the early detection, differential diagnosis and prognostic assessment of AKI. The most obvious requirements for a biomarker include its reflection of the underlying pathophysiology of the disease. Hence, a biomarker of AKI should derive from the injured kidney and reflect a molecular process intimately connected with tissue injury. Here, we provide an overview of the basic pathophysiology, the cellular sources and the clinical performance of the most important currently proposed biomarkers of AKI: neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), liver-type fatty acid-binding protein (L-FABP), interleukin-18 (IL-18), insulin-like growth factor-binding protein 7 (IGFBP7), tissue inhibitor of metalloproteinase 2 (TIMP-2) and calprotectin (S100A8/9). We also acknowledge each biomarker's advantages and disadvantages as well as important knowledge gaps and perspectives for future studies.

The serum heart-type fatty acid-binding protein (HFABP) levels can be used to detect the presence of acute kidney injury on admission in patients admitted to the non-surgical intensive care unit

Background

No cardiac biomarkers for detecting acute kidney injury (AKI) on admission in non-surgical intensive care patients have been reported. The aim of the present study is to elucidate the role of cardiac biomarkers for quickly identifying the presence of AKI on admission.

Methods

Data for 1183 patients who underwent the measurement of cardiac biomarkers, including the serum heart-type fatty acid-binding protein (s-HFABP) level, in the emergency department were screened, and 494 non-surgical intensive care patients were enrolled in this study. Based on the RIFLE classification, which was the ratio of the serum creatinine value recorded on admission to the baseline creatinine value, the patients were assigned to a no-AKI (n = 349) or AKI (Class R [n = 83], Class I [n = 36] and Class F [n = 26]) group on admission. We evaluated the diagnostic value of the s-H-FABP level for detecting AKI and Class I/F. The mid-term prognosis, as all-cause death within 180 days, was also evaluated.

Results

The s-H-FABP levels were significantly higher in the Class F (79.2 [29.9 to 200.3] ng/mL) than in the Class I (41.5 [16.7 to 71.6] ng/mL), the Class R (21.1 [10.2 to 47.9] ng/mL), and no-AKI patients (8.8 [5.4 to 17.7] ng/mL). The most predictive values for detecting AKI were Q2 (odds ratio [OR]: 3.743; 95 % confidence interval [CI]: 1.693–8.274), Q3 (OR: 9.427; 95 % CI: 4.124–21.548), and Q4 (OR: 28.000; 95 % CI: 11.245–69.720), while those for Class I/F were Q3 (OR: 5.155; 95 % CI: 1.030–25.790) and Q4 (OR: 22.978; 95 % CI: 4.814–109.668). The s-HFABP level demonstrating an optimal balance between sensitivity and specificity (70.3 and 72.8 %, respectively; area under the curve: 0.774; 95 % CI: 0.728–0.819) was 15.7 ng/mL for AKI and 20.7 ng/mL for Class I/F (71.0 and 83.1 %, respectively; area under the curve: 0.818; 95 % CI: 0.763–0.873). The prognosis was significantly poorer in the high serum HFABP with AKI group than in the other groups.

Conclusions

The s-H-FABP level is an effective biomarker for detecting AKI in non-surgical intensive care patients.

The Current State of the Diagnosis and Management of Acute Kidney Injury by Pediatric Critical Care Physicians

OBJECTIVES

Increasingly prevalent in pediatric intensive care, acute kidney injury imparts significant short- and long-term consequences. Despite advances in acute kidney injury research, clinical outcomes are worsening. We surveyed pediatric critical care physicians to describe the current state of acute kidney injury diagnosis and management in critically ill children.

DESIGN

Anonymous electronic questionnaire.

PARTICIPANTS

Pediatric critical care physicians from academic centers, the Pediatric Acute Lung Injury and Sepsis Investigators network, and/or the pediatric branch of Society of Critical Care Medicine.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of 201 surveys initiated, 170 surveys were more than 50% completed and included in our results. The majority of physicians (74%) diagnosed acute kidney injury using serum creatinine and urine output. Acute kidney injury guidelines or criteria were used routinely by 54% of physicians; Risk, Injury, Failure, Loss, and End stage criteria were the most commonly used. Awareness of any acute kidney injury guideline or definition was associated with five-fold higher odds of using any guideline (odds ratio, 5.22; 95% CI, 1.84-14.83) and four-fold higher odds of being dissatisfied with available acute kidney injury biomarkers (odds ratio, 4.88; 95% CI, 1.58-15.05). Less than half of respondents recognized the limitations of serum creatinine. Physicians unaware of the limitations of serum creatinine had two-fold higher odds of being unaware of newer biomarker availability (odds ratio, 2.34; 95% CI, 1.14-4.79). Novel biomarkers were available to 37.6% of physicians for routine use. Physicians with access to novel biomarkers more often practiced in larger (odds ratio, 3.09; 95% CI, 1.18-8.12) and Midwestern (odds ratio, 3.38; 95% CI, 1.47-7.78) institutions. More physicians with access to a novel biomarker reported satisfaction with current acute kidney injury diagnostics (66%) than physicians without access (48%); this finding approached significance (p = 0.07).

CONCLUSIONS

Half of PICU attending physicians surveyed are not using recent acute kidney injury guidelines or diagnostic criteria in their practice. There is a positive association between awareness and clinical use of acute kidney injury guidelines. Serum creatinine and urine output are still the primary diagnostics; novel biomarkers are frequently unavailable.

Urinary NGAL-Positive Acute Kidney Injury and Poor Long-term Outcomes in Hospitalized Patients

Introduction

Neutrophil gelatinase−associated lipocalin (NGAL) is a widely studied biomarker of renal tubular injury. Urinary NGAL (uNGAL) during acute kidney injury (AKI) predicts short-term adverse outcomes. However, the long-term predictive value is unknown.

Methods

We performed a prospective observational study of 145 patients with hospital-acquired AKI according to Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease (RIFLE) criteria and analyzed the long-term predictive value of uNGAL at the time of AKI. We defined a composite outcome of all-cause mortality and the development of end-stage renal disease (ESRD).

Results

In all, 61 AKI patients died and 22 developed ESRD within 6 months. The uNGAL levels were significantly higher in patients with poor long-term outcomes. uNGAL levels ≥362 μg/l (highest quartile) and uNGAL levels between 95 and 362 μg/l (third quartile) were associated with hazard ratios of 3.7 (95% confidence interval, 2.1–6.5) and 1.9 (1.1–3.5), respectively, compared with uNGAL levels <95 μg/l (lower quartiles). After 6 months, 67% and 43% of patients within the highest and third uNGAL quartile, respectively, had either progressed to ESRD or died, compared to only 21% of patients with uNGAL in the lower 2 quartiles (P < 0.001). In multivariable Cox regression analyses accounting for conventional predictors, uNGAL was the strongest independent predictor of adverse long-term outcomes. The association of uNGAL levels and poor long-term outcomes remained significant in the subgroup of 107 AKI survivors discharged without requiring dialysis (P = 0.002).

Discussion

These data indicate that elevated uNGAL levels at AKI diagnosis predict poor long-term outcomes.

Biomarkers of acute kidney injury and associations with short- and long-term outcomes

Acute kidney injury is strongly associated with increased mortality and other adverse outcomes. Medical researchers have intensively investigated novel biomarkers to predict short- and long-term outcomes of acute kidney injury in many patient care settings, such as cardiac surgery, intensive care units, heart failure, and transplant. Future research should focus on leveraging this relationship to improve enrollment for clinical trials of acute kidney injury.

Increase in urinary markers during the acute phase reflects the degree of chronic tubulointerstitial injury after ischemia-reperfusion renal injury

CONTEXT

Acute kidney injury (AKI) could lead to progressive chronic kidney disease (CKD).

OBJECTIVES

To demonstrate that urinary markers in AKI are associated with the degree of persistent renal injury.

MATERIAL AND METHODS

Human L-FABP chromosomal transgenic (T_g) mice were subjected to ischemia-reperfusion (I/R) clamping renal pedicle for 20 min or 30 min. Kidneys were obtained at one and 40 days after I/R.

RESULTS

Urinary L-FABP, NGAL, Kim-1 and albumin levels increased during the acute phase and were significantly correlated with the degree of tubulointerstitial fibrosis during the chronic phase.

DISCUSSION AND CONCLUSION

These markers could detect higher risk of progression to CKD.

Urinary L-FABP as a mortality predictor in <5-year-old children with sepsis in Bangladesh

BACKGROUND

Although sepsis is often associated with high mortality in severely malnourished children, data are very limited on appropriate diagnostic tools to predict mortality. We examined the role of urinary liver-type fatty acid-binding protein (L-FABP) in children <5 years old with sepsis who died.

METHODS

This prospective observational study was conducted at the Dhaka Hospital of the International Centre for Diarrhoeal Disease Research, Bangladesh. Children aged 6-59 months admitted with sepsis from April 2010 to December 2011 were enrolled. Comparison of clinical and laboratory characteristics was made between children who survived (n = 83) and those who did not survive (n = 22).

RESULTS

On multiple Poisson regression analysis, after adjusting for potential confounders such as mid-upper arm circumference < 115 mm, plasma albumin < 2.5 g/dL, potassium > 5.0 mmol/L, and blood urea nitrogen > 20 mg/dL on admission, first urine L-FABP ≥ 370 ng/mL (relative risk [RR], 2.76; 95%CI: 1.22-6.25), weight-for-length/height z score < -3 (RR, 2.54; 95%CI: 1.26-5.09), capillary refilling time > 2.0 s (RR, 5.16; 95%CI: 1.46-18.3), and sodium > 160 mmol/L (RR, 2.72; 95%CI: 1.07-6.90) were identified as significant risk factors of mortality in children with sepsis. Diagnostic performance of first urine L-FABP was analyzed using receiver operating characteristic curve, and the area under the curve was 0.647 (95%CI: 0.500-0.795).

CONCLUSION

Urinary L-FABP may be a useful predictor of mortality in septic children. Urinary examination is non-invasive and easy to apply at the bedside.

Long-term remote organ consequences following acute kidney injury

Acute kidney injury (AKI) has been a global health epidemic problem with soaring incidence, increased long-term risks for multiple comorbidities and mortality, as well as elevated medical costs. Despite the improvement of patient outcomes following the advancements in preventive and therapeutic strategies, the mortality rates among critically ill patients with AKI remain as high as 40–60 %. The distant organ injury, a direct consequence of deleterious systemic effects, following AKI is an important explanation for this phenomenon. To date, most evidence of remote organ injury in AKI is obtained from animal models. Whereas the observations in humans are from a limited number of participants in a relatively short follow-up period, or just focusing on the cytokine levels rather than clinical solid outcomes. The remote organ injury is caused with four underlying mechanisms: (1) “classical” pattern of acute uremic state; (2) inflammatory nature of the injured kidneys; (3) modulating effect of AKI of the underlying disease process; and (4) healthcare dilemma. While cytokines/chemokines, leukocyte extravasation, oxidative stress, and certain channel dysregulation are the pathways involving in the remote organ damage. In the current review, we summarized the data from experimental studies to clinical outcome studies in the field of organ crosstalk following AKI. Further, the long-term consequences of distant organ-system, including liver, heart, brain, lung, gut, bone, immune system, and malignancy following AKI with temporary dialysis were reviewed and discussed.

Comparison of Plasma and Urine Biomarker Performance in Acute Kidney Injury

Background

New renal biomarkers measured in urine promise to increase specificity for risk stratification and early diagnosis of acute kidney injury (AKI) but concomitantly may be altered by urine concentration effects and chronic renal insufficiency. This study therefore directly compared the performance of AKI biomarkers in urine and plasma.

Methods

This single-center, prospective cohort study included 110 unselected adults undergoing cardiac surgery with cardiopulmonary bypass between 2009 and 2010. Plasma and/or urine concentrations of creatinine, cystatin C, neutrophil gelatinase-associated lipocalin (NGAL), liver fatty acid-binding protein (L-FABP), kidney injury molecule 1 (KIM1), and albumin as well as 15 additional biomarkers in plasma and urine were measured during the perioperative period. The primary outcome was AKI defined by AKIN serum creatinine criteria within 72 hours after surgery.

Results

Biomarkers in plasma showed markedly better discriminative performance for preoperative risk stratification and early postoperative (within 24h after surgery) detection of AKI than urine biomarkers. Discriminative power of urine biomarkers improved when concentrations were normalized to urinary creatinine, but urine biomarkers had still lower AUC values than plasma biomarkers. Best diagnostic performance 4h after surgery had plasma NGAL (AUC 0.83), cystatin C (0.76), MIG (0.74), and L-FAPB (0.73). Combinations of multiple biomarkers did not improve their diagnostic power. Preoperative clinical scoring systems (EuroSCORE and Cleveland Clinic Foundation Score) predicted the risk for AKI (AUC 0.76 and 0.71) and were not inferior to biomarkers. Preexisting chronic kidney disease limited the diagnostic performance of both plasma and urine biomarkers.

Conclusions

In our cohort plasma biomarkers had higher discriminative power for risk stratification and early diagnosis of AKI than urine biomarkers. For preoperative risk stratification of AKI clinical models showed similar discriminative performance to biomarkers. The discriminative performance of both plasma and urine biomarkers was reduced by preexisting chronic kidney disease.

Plasma neutrophil gelatinase-associated lipocalin predicts major adverse cardiovascular events after cardiac care unit discharge

BACKGROUND

Emerging acute kidney injury biomarkers, including neutrophil gelatinase-associated lipocalin (NGAL), have a high potential for predicting worsening renal function. Acute exacerbation of renal dysfunction has a great impact on the outcomes of cardiovascular patients in critical conditions. This study aimed to evaluate whether plasma NGAL can predict the mortality and major adverse cardiovascular events (MACEs) after discharge from the cardiac care unit (CCU).

METHODS

Patients who were admitted to the CCU of the Tokyo University Hospital were prospectively enrolled (101 patients). Blood and urinary markers, including the blood NGAL, brain natriuretic peptide, creatinine, cystatin C, urinary albumin, N-acetyl-β-d-glucosaminidase, and L-type fatty acid-binding protein, were measured at CCU discharge. The primary outcome was MACEs until at least 6 months after CCU discharge.

RESULTS

Thirty-five patients experienced MACEs (35%). Multivariate logistic analysis revealed that the plasma NGAL, length of CCU stay, and existence of diabetes and heart failure were independent predicting factors for MACEs. Patients with the highest NGAL at discharge (>75th percentile) showed a significantly higher risk of MACEs than those with the lowest NGAL (<25th percentile) (log-rank test; hazard ratio, 5.15; 95% confidence interval 1.84-18.20; p<0.01).

CONCLUSION

Plasma NGAL at CCU discharge is a significant prognostic indicator of outcomes at 6 months in critically ill cardiac patients treated in a CCU.

Diagnosis of acute kidney injury: Kidney Disease Improving Global Outcomes criteria and beyond

PURPOSE OF REVIEW

Acute kidney injury (AKI) is common. Clear criteria and accurate diagnostic tools are essential to diagnose AKI early and correctly. The aims of this review are to outline some of the pitfalls of the Kidney Disease Improving Global Outcomes (KDIGO) classification and to describe other traditional and novel tools to diagnose AKI.

RECENT FINDINGS

The KDIGO classification of AKI is based on changes in serum creatinine and urine output. Misdiagnosis of AKI can occur when using only the KDIGO criteria. Potential pitfalls are related to the fact that neither creatinine nor urine output are renal-specific. Other traditional tools to diagnose AKI are blood urea nitrogen, urine chemistry, urine microscopy and renal biopsy. New diagnostic tools, including novel AKI biomarkers and techniques to measure glomerular filtration rate in real time, are being developed and validated.

SUMMARY

Knowledge about the strengths and weaknesses of traditional diagnostic tests is essential to make the correct diagnosis of AKI. New tests and technical innovations offer the prospect of diagnosing AKI earlier and more accurately.

Intra-abdominal hypertension does not predict renal recovery or in-hospital mortality in critically ill patients with acute kidney injury

BACKGROUND

Although emerging evidence suggests that intra-abdominal hypertension (IAH) is a predictor of the development of acute kidney injury (AKI), it remains unclear whether the presence of IAH is a predictor of prognosis in patients with AKI. The purpose of this study was to assess whether the presence of IAH could predict prognosis in critically ill patients with AKI. The prognostic value of urinary biomarkers was also determined.

METHODS

In this prospective observational study, we enrolled 57 patients with established AKI, who were admitted to the intensive care unit between February 2012 and June 2014. IAH was defined as a sustained elevation in intra-abdominal pressure of ≥12 mmHg, in three consecutive measurements performed daily on the first 3 days. Urinary neutrophil gelatinase-associated lipocalin (NGAL), liver-type fatty acid-binding protein, and simplified acute physiology score II score at the time of admission were also examined.

RESULTS

IAH was observed in 78.9% of patients. The in-hospital mortality was 21.1%, and renal recovery during hospitalization was achieved in 40.4% of patients. Although high urinary NGAL [odds ratio (OR), 1.015] and liver-type fatty acid-binding protein (OR, 1.003) were found to be independent predictors of renal recovery, IAH was not. High urinary NGAL (OR, 1.003) and a high simplified acute physiology score II score (OR, 1.102) were independent predictors of in-hospital mortality, while IAH or urinary liver-type fatty acid-binding protein was not.

CONCLUSION

Although IAH is prevalent in critically ill patients with AKI, it did not predict AKI prognosis. However, urinary NGAL was found to be a useful predictor of both renal recovery and in-hospital mortality.

Novel markers and therapies for patients with acute heart failure and renal dysfunction

BACKGROUND

Acute kidney injury complicates decompensated heart failure in ∼33% of cases and is associated with morbidity and mortality; thus, we sought to systematically review this topic in order to summarize novel diagnostic and therapeutic approaches.

METHODS

Structured PubMed searches on these topics were conducted in February 2014 and relevant literature was identified. The PubMed search identified a total of 192 articles that were individually screened for inclusion in this analysis, and 58 were included.

RESULTS

Acute kidney injury, defined by substantial increases in serum creatinine, is associated consistently with prolonged length of stay, rehospitalization, and mortality. Biomarker studies suggested that natriuretic peptides are prognostic for shorter- and longer-term mortality. Novel proteins indicating kidney damage and albumin in the urine are associated with acute kidney injury. The most promising acute pharmacologic treatment appears to be serelaxin, which has been shown to improve acute heart failure symptoms, hemodynamic parameters, and renal function.

CONCLUSIONS

The presence of acute kidney injury results in worse clinical outcomes for patients with acute heart failure. Novel biomarkers and therapies hold the promise of improving both cardiac and renal outcomes in these patients.

The ratio of plasma interleukin-18 is a sensitive biomarker for acute kidney injury after liver transplantation

BACKGROUND

Acute kidney injury (AKI) is common after liver transplantation (OLT) and is associated with high morbidity and mortality. Previous studies have shown that interleukin-18 (IL-18) levels are associated with AKI. The purpose of this study was to determine whether plasma IL-18 levels were early predictors for AKI after liver transplantation.

METHODS

Plasma samples were obtained from 26 patients who underwent OLT at induction of anesthesia (T1), 1 hour after the surgical incision (T2), the time of reperfusion (T3), as well as 1 (T4), 2 (T5), and 4 hours (T6) after reperfusion. Samples were also obtained at 24 hours after surgery (T7). The AKI criteria were taken according to the Acute Kidney Injury Network criteria.

RESULTS

Twelve patients (46%) developed AKI after OLT. The area under the receiver operating curve of plasma IL-18 concentrations (T4/T1) to predict AKI occurrence was 0.842 at T5, 0.905 at T6, 0.726 at T7, and 0.726 at T5 to T7.

CONCLUSION

Plasma IL-18 concentrations taken 1 hour after reperfusion were predictive of AKI. Therefore, changing IL-18 ratio may be an early predictor for AKI after OLT.

The urinary levels of prostanoid metabolites predict acute kidney injury in heterogeneous adult Japanese ICU patients: a prospective observational study

BACKGROUND

Acute kidney injury (AKI) is frequently observed in critically ill patients in the intensive care unit (ICU) and is associated with increased mortality. Prostanoids regulate numerous biological functions, including hemodynamics and renal tubular transport. We herein investigated the ability of urinary prostanoid metabolites to predict the onset of AKI in critically ill adult patients.

METHODS

The current study was conducted as a prospective observational study. Urine of patients admitted to the ICU at Okayama University Hospital was collected and the urinary levels of prostaglandin E2 (PGE2), PGI2 metabolite (2,3-dinor-6-OXO-PGF1α), thromboxane A2 (TXA2) metabolite (11-dehydro-TXB2) were determined.

RESULTS

Of the 93 patients, 24 developed AKI (AKIN criteria). Surgical intervention (93, 75 %) was the leading cause of ICU admission. Overall, the ratio of the level of serum Cr on Day 1 after ICU admission to that observed at baseline positively correlated with the urinary 2,3-dinor-6-OXO-PGF1α/Cr (r = 0.57, p < 0.0001) and 11-dehydro-TXB2/Cr (r = 0.47, p < 0.0001) ratios. In 16 cases of de novo AKI, the urinary 2,3-dinor-6-OXO-PGF1α/Cr and 11-dehydro-TXB2/Cr values were significantly elevated compared with that observed in the non-AKI group, whereas the urinary PGE2/Cr values were not. The urinary 2,3-dinor-6-OXO-PGF1α/Cr ratio exhibited the best diagnostic and predictive performance among the prostanoid metabolites according to the receiver operating characteristic (ROC) analysis [ROC-area under the curve (AUC): 0.75].

CONCLUSIONS

Taken together, these results demonstrate that the urinary 2,3-dinor-6-OXO-PGF1α/Cr and 11-dehydro-TXB2/Cr ratios are associated with the subsequent onset of AKI and poor outcomes in adult heterogeneous ICU patients.

Predictive value of NGAL for use of renal replacement therapy in patients with severe sepsis

BACKGROUND

The predictive value of plasma and urine neutrophil gelatinase-associated lipocalin (NGAL) for use of renal replacement therapy (RRT) and acute kidney injury (AKI) is not established in patients with severe sepsis.

METHODS

This was a prospective observational study in three general intensive care units (ICUs) in adult ICU patients with severe sepsis needing fluid resuscitation and a sub-study of the 6S trial. Plasma and urine were sampled at baseline and NGAL was measured using particle-enhanced turbidimetric immunoassay (The NGAL Test). Outcome measures were use of RRT in ICU, development of AKI according to the Kidney Disease: Improving Global Outcomes plasma creatinine criteria within 48 h and 90-day mortality.

RESULTS

Two-hundred- twenty-two patients had samples taken (211 had plasma and 162 urine sampled); simplified acute physiology score II was 54 (39-66). Forty patients (18%) had RRT in the ICU, 91 patients had AKI at enrollment; of the remaining 131 patients 24% developed AKI during the first 48 h, and 55% had died at 90 days. Areas under receiver-operating characteristics curve (AuROC) for predicting use of RRT in ICU were 0.70 (95% confidence interval 0.61-0.78) and 0.62 (0.51-0.73) for plasma and urine NGAL, respectively. AuROC of plasma and urine NGAL for AKI were 0.66 (0.54-0.77) and 0.71 (0.59-0.82), respectively, and for 90-day mortality 0.55 (0.47-0.63) and 0.61 (0.53-0.70), respectively. Combining NGAL values with plasma creatinine did not improve AuROCs.

CONCLUSION

In ICU patients with severe sepsis, plasma and urine NGAL had low predictive power for use of RRT, AKI and 90-day mortality. These results were supported by sensitivity and exploratory analyses.

Evaluation of urinary tissue inhibitor of metalloproteinase-2 in acute kidney injury: a prospective observational study

INTRODUCTION

Tissue inhibitor of metalloproteinase-2 (TIMP-2) is an emerging acute kidney injury (AKI) biomarker. We evaluated the performance of urinary TIMP-2 in an adult mixed ICU by comparison with other biomarkers that reflect several different pathways of AKI.

METHODS

In this study, we prospectively enrolled 98 adult critically ill patients who had been admitted to the adult mixed ICU. Urinary TIMP-2 and N-acetyl-β-D-glucosaminidase (NAG) and plasma neutrophil gelatinase-associated lipocalin (NGAL), interleukin-6 (IL-6) and erythropoietin (EPO) were measured on ICU admission. We evaluated these biomarkers' capability of detecting AKI and its severity as determined by using the Kidney Disease Improving Global Outcomes serum creatinine criteria, as well as its capacity to predict in-hospital mortality. The impact of sepsis, the leading cause of AKI in ICUs, was also evaluated.

RESULTS

We found AKI in 42 patients (42.9%). All biomarkers were significantly higher in AKI than in non-AKI. In total, 27 patients (27.6%) developed severe AKI. Urinary TIMP-2 was able to distinguish severe AKI from non-severe AKI with an area under the receiver operating characteristic curve (AUC-ROC) of 0.80 (95% confidence interval, 0.66 to 0.90). A total of 41 cases (41.8%) were complicated with sepsis. Although plasma NGAL and IL-6 were increased by sepsis, urinary TIMP-2 and NAG were increased not by sepsis, but by the presence of severe AKI. Plasma EPO was increased only by septic AKI. In-hospital mortality was 15.3% in this cohort. Urinary TIMP-2 and NAG, and plasma NGAL, were significantly higher in non-survivors than in survivors, although plasma IL-6 and EPO were not. Among the biomarkers, only urinary TIMP-2 was able to predict in-hospital mortality significantly better than serum creatinine.

CONCLUSION

Urinary TIMP-2 can detect severe AKI with performance equivalent to plasma NGAL and urinary NAG, with an AUC-ROC value higher than 0.80. Furthermore, urinary TIMP-2 was associated with mortality. Sepsis appeared to have only a limited impact on urinary TIMP-2, in contrast to plasma NGAL.

Academic College of Emergency Experts in India's INDO-US Joint Working Group and OPUS12 Foundation Consensus Statement on Creating A Coordinated, Multi-Disciplinary, Patient-Centered, Global Point-of-Care Biomarker Discovery Network

Biomarker science brings great promise to clinical medicine. This is especially true in the era of technology miniaturization, rapid dissemination of knowledge, and point-of-care (POC) implementation of novel diagnostics. Despite this tremendous progress, the journey from a candidate biomarker to a scientifically validated biomarker continues to be an arduous one. In addition to substantial financial resources, biomarker research requires considerable expertise and a multidisciplinary approach. Investigational designs must also be taken into account, with the randomized controlled trial remaining the “gold standard”. The authors present a condensed overview of biomarker science and associated investigational methods, followed by specific examples from clinical areas where biomarker development and/or implementation resulted in tangible enhancements in patient care. This manuscript also serves as a call to arms for the establishment of a truly global, well-coordinated infrastructure dedicated to biomarker research and development, with focus on delivery of the latest discoveries directly to the patient via point-of-care technology.

Mortality prediction by acute kidney injury biomarkers in comparison with serum creatinine

OBJECTIVES

To investigate the performance of acute kidney injury (AKI) biomarkers for mortality prediction.

MATERIALS AND METHODS

Cutoff values of urinary L-type fatty acid-binding protein (L-FABP) and N-acetyl-β-d-glucosaminidase (NAG) for AKI diagnosis in ICU were determined in the derivation cohort. The performance of these AKI biomarkers for mortality prediction was evaluated in the validation cohort with stratification of serum-creatinine based AKI diagnosis.

RESULTS

Mortality in the AKI patients diagnosed by serum creatinine was increased remarkably when urinary L-FABP and NAG were positive.

CONCLUSIONS

These AKI biomarkers can specifically detect high-risk patients among creatinine-base diagnosed AKI.

Urinary L-FABP predicts poor outcomes in critically ill patients with early acute kidney injury

Biomarker studies for early detection of acute kidney injury (AKI) have been limited by non-selective testing and uncertainties in using small changes in serum creatinine as a reference standard. Here we examine the ability of urine L-type fatty acid binding protein (L-FABP), neutrophil gelatinase-associated lipocalin (NGAL), Interleukin-18 (IL-18), and Kidney Injury Moledule-1 (KIM-1) to predict injury progression, dialysis, or death within 7 days in critically ill adults with early AKI. Of 152 patients with known baseline creatinine examined, 36 experienced the composite outcome. Urine L-FABP demonstrated an area under the receiver-operating characteristic curve (AUC-ROC) of 0.79 (95% confidence interval 0.70-0.86), which improved to 0.82 (95% confidence interval 0.75-0.90) when added to the clinical model (AUC-ROC of 0.74). Urine NGAL, IL-18, and KIM-1 had AUC-ROCs of 0.65, 0.64, and 0.62, respectively, but did not significantly improve discrimination of the clinical model. The category free net reclassification index improved with urine L-FABP [total net reclassification index for non-events 31.0%] and urine NGAL [total net reclassification index for events 33.3%]. However, only urine L-FABP significantly improved the integrated discriminative index. Thus, modest early changes in serum creatinine can help target biomarker measurement for determining prognosis with urine L-FABP providing independent and additive prognostic information when combined with clinical predictors.

Neutrophil gelatinase-associated lipocalin and liver-type fatty acid-binding protein as biomarkers for acute kidney injury after organ transplantation

PURPOSE

Neutrophil gelatinase-associated lipocalin (NGAL) and liver-type fatty acid-binding protein (L-FABP) are promising early biomarkers for acute kidney injury (AKI). In organ transplant recipients, AKI predictability based on NGAL and L-FABP remains to be elucidated. Furthermore, the association between serial NGAL and L-FABP measurements and AKI outcome is unknown. Therefore, we conducted a study to evaluate the ability of NGAL and L-FABP to predict AKI after organ transplantation and investigate the association between NGAL, L-FABP and AKI outcome.

METHODS

Twenty-five organ transplant recipients admitted to the intensive care unit (ICU) immediately after transplant surgery were studied prospectively. Plasma NGAL (P-NGAL), urinary NGAL (U-NGAL) and L-FABP were measured from ICU admission to ICU discharge. U-NGAL and L-FABP were corrected for dilution/concentration by calculating U-NGAL/urine creatinine ratios (U-NGAL/Cr) and L-FABP/urine creatinine ratios (L-FABP/Cr). AKI was defined according to the Kidney Disease: Improving Global Outcomes criteria.

RESULTS

AKI occurred in 11 patients. P-NGAL, U-NGAL/Cr and L-FABP/Cr upon ICU admission were unrelated to AKI development (p = 0.24, 0.22, and 0.53, respectively). There were no differences in P-NGAL, U-NGAL/Cr, and L-FABP/Cr levels from day 1 to day 6 between patients who did not recover from AKI and patients who recovered from AKI (p = 0.82, 0.26, and 0.61, respectively).

CONCLUSION

Our findings suggest that NGAL and L-FABP upon ICU admission are not predictive of AKI and serial NGAL and L-FABP measurements may be ineffective for monitoring the status and treatment of post-transplantation AKI.

The urine protein NGAL predicts renal replacement therapy, but not acute kidney injury or 90-day mortality in critically ill adult patients

BACKGROUND

Urine neutrophil gelatinase-associated lipocalin (uNGAL) is increasingly used as a biomarker for acute kidney injury (AKI). However, the clinical value of uNGAL with respect to AKI, renal replacement therapy (RRT), or 90-day mortality in critically ill patients is unclear. Accordingly, we tested the hypothesis that uNGAL is a clinically relevant biomarker for these end points in a large, nonselected cohort of critically ill adult patients.

METHODS

We prospectively obtained urine samples from 1042 adult patients admitted to 15 Finnish intensive care units. We analyzed 3 samples (on admission, at 12 hours, and at 24 hours) with NGAL ELISA Rapid Kits (BioPorto® Diagnostics, Gentofte, Denmark). We chose the highest uNGAL (uNGAL24) for statistical analyses. We calculated the areas under receiver operating characteristics curves (AUC) with 95% confidence intervals (95% CIs), the best cutoff points with the Youden index, positive likelihood ratios (LR+), continuous net reclassification improvement (NRI), and the integrated discrimination improvement (IDI). We performed sensitivity analyses excluding patients with AKI or RRT on day 1, sepsis, or with missing baseline serum creatinine concentration.

RESULTS

In this study population, the AUC of uNGAL24 (95% CI) for development of AKI (defined by the Kidney Disease: Improving Global Outcomes [KDIGO] criteria) was 0.733 (0.701-0.765), and the continuous NRI for AKI was 56.9%. For RRT, the AUC of uNGAL24 (95% CI) was 0.839 (0.797-0.880), and NRI 56.3%. For 90-day mortality, the AUC of uNGAL24 (95% CI) was 0.634 (0.593 to 0.675), and NRI 15.3%. The LR+ (95% CI) for RRT was 3.81 (3.26-4.47).

CONCLUSION

In this study, we found that uNGAL associated well with the initiation of RRT but did not provide additional predictive value regarding AKI or 90-day mortality in critically ill patients.

Urine YKL-40 is associated with progressive acute kidney injury or death in hospitalized patients

Background

A translational study in renal transplantation suggested YKL-40, a chitinase 3-like-1 gene product, plays an important role in acute kidney injury (AKI) and repair, but data are lacking about this protein in urine from native human kidneys.

Methods

This is an ancillary study to a single-center, prospective observational cohort of patients with clinically-defined AKI according to AKI Network serum creatinine criteria. We determined the association of YKL -40 ≥ 5 ng/ml, alone or combined with neutrophil gelatinase-associated lipocalin (NGAL), in urine collected on the first day of AKI with a clinically important composite outcome (progression to higher AKI stage and/or in-hospital death).

Results

YKL-40 was detectable in all 249 patients, but urinary concentrations were considerably lower than in previously measured deceased-donor kidney transplant recipients. Seventy-two patients (29%) progressed or died in-hospital, and YKL-40 ≥ 5 ng/ml had an adjusted odds ratio (95% confidence interval) for the outcome of 3.4 (1.5-7.7). The addition of YKL-40 to a clinical model for predicting the outcome resulted in a continuous net reclassification improvement of 29% (P = 0.04). In patients at high risk for the outcome based on NGAL concentrations in the upper quartile, YKL-40 further partitioned the cohort into moderate-risk and very high-risk groups.

Conclusions

Urine YKL-40 is associated with AKI progression and/or death in hospitalized patients and improves clinically determined risk reclassification. Combining YKL-40 with other AKI biomarkers like NGAL may further delineate progression risk, though additional studies are needed to determine whether YKL-40 has general applicability and to define its association with longer-term outcomes in AKI.

Biomarkers of AKI: a review of mechanistic relevance and potential therapeutic implications

AKI is a common clinical condition associated with a number of adverse outcomes. More timely diagnosis would allow for earlier intervention and could improve patient outcomes. The goal of early identification of AKI has been the primary impetus for AKI biomarker research, and has led to the discovery of numerous novel biomarkers. However, in addition to facilitating more timely intervention, AKI biomarkers can provide valuable insight into the molecular mechanisms of this complex and heterogeneous disease. Furthermore, AKI biomarkers could also function as molecular phenotyping tools that could be used to direct clinical intervention. This review highlights the major studies that have characterized the diagnostic and prognostic predictive power of these biomarkers. The mechanistic relevance of neutrophil gelatinase-associated lipocalin, kidney injury molecule 1, IL-18, liver-type fatty acid-binding protein, angiotensinogen, tissue inhibitor of metalloproteinase-2, and IGF-binding protein 7 to the pathogenesis and pathobiology of AKI is discussed, putting these biomarkers in the context of the progressive phases of AKI. A biomarker-integrated model of AKI is proposed, which summarizes the current state of knowledge regarding the roles of these biomarkers and the molecular and cellular biology of AKI.

Biomarkers in cardiorenal syndromes

Cardiac and renal diseases often coexist and patients with cardiac and renal failure have high morbidity and mortality. Cardiorenal syndromes (CRSs) are disorders of the heart and kidneys whereby dysfunction in one organ may induce dysfunction in the other organ. Five subtypes of CRSs have been defined by the Acute Dialysis Quality Initiative Consensus Group. There is a need for early detection and monitoring of patients with CRSs. Biomarkers play a key role in the diagnosis and monitoring of acute myocardial infarction, chronic heart failure, and chronic kidney disease. In recent years, new biomarkers have been identified that may play a role in the early diagnosis of acute kidney injury. Herein, we review the use of serum and urine biomarkers in the diagnosis and management of CRSs. The established cardiac and renal biomarkers such as the cardiac troponins, natriuretic peptides, urine albumin, and creatinine, as well as the new renal biomarkers cystatin C and neutrophil gelatinase-associated lipocalin are reviewed in detail. The recent advances in assay methods, clinical studies, and recommendations in clinical guidelines are discussed. With advances in biomarker research, in future, perhaps a multimarker approach will become feasible to stratify the diagnosis of CRS for individualized treatment and prognosis.

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.

Response of urinary liver-type fatty acid-binding protein to contrast media administration has a potential to predict one-year renal outcome in patients with ischemic heart disease

Urinary liver-type fatty acid-binding proteins (uL-FABP) have recently been recognized as a useful biomarker for predicting contrast-induced nephropathy. Although accumulating studies have evaluated short-term outcomes, its prognostic value for long-term renal prognosis in patients undergoing coronary angiography (CAG) has not been fully examined. This study aimed to evaluate the predictive value of uL-FABP for long-term renal outcome in patients with ischemic heart disease (IHD). Consecutive 24 patients with impaired renal function (serum creatinine >1.2 mg/dL) who underwent CAG were enrolled. uL-FABP was measured before CAG, 24 and 48 h after CAG. The changes in estimated glomerular filtration rate (eGFR) throughout CAG and at 1 year later were compared with the uL-FABP levels. The patients with a greater decrease in eGFR 1 year later had higher uL-FABP levels at all points, but only the value at 48 h after CAG reached statistical significance (lower vs. higher decreased eGFR group, 4.61 ± 3.87 vs. 17.71 ± 12.96; P < 0.01). Measurement of uL-FABP at 48 h after CAG (48h-uL-FABP) showed better correlation with the change in eGFR (pre-CAG uL-FABP vs. 48h-uL-FABP: R = 0.27, P = 0.20 vs. R = 0.65, P < 0.01). Moreover, the high-pre and high-48h-uL-FABP group showed a significantly larger decrease in eGFR compared with the high-pre and low-48h-uL-FABP group (change in eGFR; 8.12 ± 4.06 vs. 1.25 ± 2.23 mL/min/1.73 m2, P < 0.01), although the baseline eGFR levels were similar between these two groups. In this pilot study, measurement of uL-FABP levels at 48 h after CAG may be useful in detecting renal damage, and in predicting 1-year renal outcome in IHD patients undergoing CAG.

Tenofovir use and urinary biomarkers among HIV-infected women in the Women's Interagency HIV Study (WIHS)

BACKGROUND

Tenofovir (TDF) has been associated with renal tubular injury. Biomarkers that signal early tubular dysfunction are needed because creatinine rise lags behind TDF-associated kidney dysfunction. We examined several urinary biomarkers to determine if rises accompanying TDF initiation preceded creatinine changes.

METHODS

Three urinary biomarkers of tubular impairment--neutrophil gelatinase-associated lipocalin (NGAL), N-acetyl-β-D-glucosaminidase (NAG), and β-2-microglobulin (β2MG)--were measured across 3 time points (one pre-TDF visit and 2 post-TDF visits) in 132 HIV-positive women from the Women's Interagency HIV Study. Women initiating highly active antiretroviral therapy (HAART) containing TDF were propensity score matched to women initiating HAART without TDF and women not on HAART.

RESULTS

There were no differences between groups for NGAL or NAG, but β2MG was 19 times more likely to be elevated among TDF users at the second post-TDF visit compared with non-TDF users at the pre-TDF visit (P < 0.01). History of proteinuria was associated with elevated NGAL (P < 0.01). Factors associated with elevated NAG were glomerular filtration rate <60 mL/minute, history of proteinuria, hepatitis C (P < 0.01 for all), and diabetes mellitus (P = 0.05). Factors associated with increased odds of elevated β2MG were HIV RNA >100,000 copies/mL, hepatitis C, boosted protease inhibitor use, and glomerular filtration rate <60 mL/minute (P ≤ 0.01 for all).

CONCLUSIONS

β2MG levels are elevated in women on TDF, indicating probable early renal dysfunction. Biomarker elevation is additionally associated with baseline chronic kidney disease, uncontrolled viremia, and boosted protease inhibitor use. Future studies are needed to explore urinary biomarker thresholds in identifying treated HIV-infected individuals at risk for renal dysfunction.

Repulsive guidance cue semaphorin 3A in urine predicts the progression of acute kidney injury in adult patients from a mixed intensive care unit

BACKGROUNDS

Predicting the development of acute kidney injury (AKI) in the critical care setting is challenging. Although several biomarkers showed somewhat satisfactory performance for detecting established AKI even in a heterogeneous disease-oriented population, identification of new biomarkers that predict the development of AKI accurately is urgently required.

METHODS

A single-center prospective observational cohort study was undertaken to evaluate for the first time the reliability of the newly identified biomarker semaphorin 3A for AKI diagnosis in heterogeneous intensive care unit populations. In addition to five urinary biomarkers of L-type fatty acid-binding protein (L-FABP), neutrophil gelatinase-associated lipocalin (NGAL), IL-18, albumin and N-acetyl-β-d-glucosaminidase (NAG), urinary semaphorin 3A was measured at intensive care unit (ICU) admission.

RESULTS AND CONCLUSION

Three hundred thirty-nine critically ill adult patients were recruited for this study. Among them, 131 patients (39%) were diagnosed with AKI by the RIFLE criteria and 66 patients were diagnosed as AKI at post-ICU admission (later-onset AKI). Eighty-four AKI patients showed worsening severity during 1 week observation (AKI progression). Although L-FABP, NGAL and IL-18 showed significantly higher area under the curve (AUC)-receiver operating characteristic (ROC) values than semaphorin 3A in detecting established AKI, semaphorin 3A was able to detect later-onset AKI and AKI progression with similar AUC-ROC values compared with the other five biomarkers [AUC-ROC (95% CI) for established AKI 0.64 (0.56-0.71), later-onset AKI 0.71 (0.64-0.78), AKI progression 0.71 (0.64-0.77)]. Urinary semaphorin 3A was not increased in non-progressive established AKI, while the other biomarkers were elevated regardless of further progression. Finally, sepsis did not have any impact on semaphorin 3A while the other urinary biomarkers were increased with sepsis. Semaphorin 3A is a new biomarker of AKI which may have a distinct predictive use for AKI progression when compared with other AKI biomarkers.

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.

Urinary interleukin 18 for detection of acute kidney injury: a meta-analysis

BACKGROUND

Interleukin 18 (IL-18) has been proposed as a biomarker for the early detection of acute kidney injury (AKI), but a broad range of its predictive accuracy has been reported.

STUDY DESIGN

Meta-analysis of diagnostic test studies.

SETTING & POPULATION

Various clinical settings of AKI, including after cardiac surgery, after contrast infusion, in the emergency department, or in the intensive care unit.

SELECTION CRITERIA FOR STUDIES

Prospective studies that investigated the diagnostic accuracy of IL-18 level to predict AKI.

INDEX TESTS

Increasing or increased urinary IL-18 excretion.

REFERENCE TESTS

The primary outcome was AKI development, mainly based on serum creatinine level (definition varied across studies). The other outcome was in-hospital mortality.

RESULTS

We analyzed data from 23 studies and 7 countries involving 4,512 patients. Of these studies, 18 could be included in the meta-analysis. Across all settings, the diagnostic odds ratio (DOR) for urinary IL-18 level to predict AKI was 4.22 (95% CI, 2.90-6.14), with sensitivity and specificity of 0.58 and 0.75, respectively. The area under the receiver operating characteristic curve (AUROC) of urinary IL-18 level to predict AKI was 0.70 (95% CI, 0.66-0.74). Subgroup analysis showed the DOR/AUROC of urinary IL-18 was 5.32 (95% CI, 2.92-9.70)/0.72 (95% CI, 0.68-0.76) in cardiac surgery patients and 3.65 (95% CI, 1.88-7.10)/0.66 (95% CI, 0.62-0.70) in intensive care unit or coronary care unit patients. After stratification for age, IL-18 level had better diagnostic accuracy in children and adolescents versus adults: 8.12 (95% CI, 3.79-17.41)/0.78 (95% CI, 0.75-0.82) versus 3.31 (95% CI, 2.28-4.80)/0.66 (95% CI, 0.62-0.70). There was no significant difference in predictive performance of urinary IL-18 level among various times.

LIMITATIONS

Various clinical settings; different definition of AKI and serum creatinine level as the reference standard test for the diagnosis of AKI.

CONCLUSIONS

Urinary IL-18 is a useful biomarker of AKI with moderate predictive value across all clinical settings.

[Biomarkers of acute kidney injury: a « trending topic » in cirrhosis]

Acute kidney injury (AKI) is an ominous event in the natural history of cirrhosis. The differential diagnosis of this entity is hampered by the absence of specific biomarkers of tubular damage in cirrhosis. The clinical usefulness of such biomarkers is determined by their effectiveness in the diagnosis of AKI and their ability to provide critical information to ameliorate clinical outcomes and survival. The lack of biomarkers has hindered the development of interventions aimed to improve the prognosis of kidney impairment in cirrhosis. Currently, biomarkers are an area of intense research in nephrology. Emerging genomic and proteomic technologies have revealed novel plasma and urinary biomarkers of AKI. The present article discusses the most promising candidate biomarkers with potential application in cirrhosis, such as NGAL, KIM-1, cystatin-C, IL-18, L-FABP, N-acetyl glucosaminidase and netrin-1, are discussed below.

Distinct injury markers for the early detection and prognosis of incident acute kidney injury in critically ill adults with preserved kidney function

The use of novel biomarkers to detect incident acute kidney injury (AKI) in the critically ill is hindered by heterogeneity of injury and the potentially confounding effects of prevalent AKI. Here we examined the ability of urine NGAL (NGAL), L-type Fatty Acid Binding Protein (L-FABP), and Cystatin C to predict AKI development, death, and dialysis in a nested case-control study of 380 critically ill adults with an eGFR over 60 ml/min/1.73 m². One-hundred thirty AKI cases were identified following biomarker measurement and were compared to 250 controls without AKI. Areas under the receiver-operator characteristic curves (AUC-ROCs) for discriminating incident AKI from non-AKI were 0.58(95%CI: 0.52-0.64), 0.59(0.52-0.65), and 0.50(0.48-0.57) for urine NGAL, L-FABP, and Cystatin C, respectively. The combined AUC-ROC for NGAL and L-FABP was 0.59(56-0.69). Both urine NGAL and L-FABP independently predicted AKI during multivariate regression; however, risk reclassification indices were mixed. Neither urine biomarker was independently associated with death or acute dialysis [NGAL hazard ratio 1.35(95%CI: 0.93-1.96), L-FABP 1.15(0.82-1.61)] though both independently predicted the need for acute dialysis [NGAL 3.44(1.73-6.83), L-FABP 2.36(1.30-4.25)]. Thus, urine NGAL and L-FABP independently associated with the development of incident AKI and receipt of dialysis but exhibited poor discrimination for incident AKI using conventional definitions.

Implementation of novel biomarkers in the diagnosis, prognosis, and management of acute kidney injury: executive summary from the tenth consensus conference of the Acute Dialysis Quality Initiative (ADQI)

Detection of acute kidney injury is undergoing a dynamic revolution of biomarker technology allowing greater, earlier, and more accurate determination of diagnosis, prognosis, and with powerful implication for management. Biomarkers can be broadly considered as any measurable biologic entity or process that allows differentiation between normal function and injury or disease. The ADQI (Acute Dialysis Quality Initiative) had its Ninth Consensus Conference dedicated to synthesis and formulation of the existing literature on biomarkers for the detection of acute kidney injury in a variety of settings. In the papers that accompany this summary, ADQI workgroups fully develop key concepts from a summary of the literature in the domains of early diagnosis, differential diagnosis, prognosis and management, and concurrent physiologic and imaging measures.