The role of urinary liver-type fatty acid-binding protein in critically ill patients

Review of the limitations of current biomarkers in acute kidney injury clinical practices

Acute kidney injury is a prevalent disease in hospitalized patients and is continuously increasing worldwide. Various efforts have been made to define and classify acute kidney injury to understand the progression of this disease. Furthermore, deviations from structure and kidney function and the current diagnostic guidelines are not adequately placed due to baseline serum creatinine values, which are rarely known and estimated based on glomerular function rate, resulting in misclassification of acute kidney injury staging. Hence, the current guidelines are still developing to improve and understand the clinical implications of risk factors and earlier predictive biomarkers of acute kidney injury. Yet, studies have indicated disadvantages and limitations with the current acute kidney injury biomarkers, including lack of sensitivity and specificity. Therefore, the present narrative review brings together the most current evidenced-based practice and literature associated with the limitations of the gold standard for acute kidney injury diagnoses, the need for novel acute kidney injury biomarkers, and the process for biomarkers to be qualified for diagnostic use under the following sections and themes. The introduction section situates the anatomy and normal and abnormal kidney functions related to acute kidney injury disorders. Guidelines in providing acute kidney injury definitions and classification are then considered, followed by a discussion of the disadvantages of standard markers used to diagnose acute kidney injury. Characteristics of an ideal acute kidney injury biomarker are discussed concerning sensitivity, specificity, and anatomic location of injury. A particular focus on the role and function of emerging biomarkers is discussed in relation to their applications and significance to the prognosis and severity of acute kidney injury. Findings show emerging markers are early indicators of acute kidney injury prediction in different clinical settings. Finally, the process required for a biomarker to be applied for diagnostic use is explained.

Comparative accuracy of biomarkers for the prediction of hospital-acquired acute kidney injury: a systematic review and meta-analysis

Background

Several biomarkers have been proposed to predict the occurrence of acute kidney injury (AKI); however, their efficacy varies between different trials. The aim of this study was to compare the predictive performance of different candidate biomarkers for AKI.

Methods

In this systematic review, we searched PubMed, Medline, Embase, and the Cochrane Library for papers published up to August 15, 2022. We selected all studies of adults (> 18 years) that reported the predictive performance of damage biomarkers (neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), liver-type fatty acid-binding protein (L-FABP)), inflammatory biomarker (interleukin-18 (IL-18)), and stress biomarker (tissue inhibitor of metalloproteinases-2 × insulin-like growth factor-binding protein-7 (TIMP-2 × IGFBP-7)) for the occurrence of AKI. We performed pairwise meta-analyses to calculate odds ratios (ORs) and 95% confidence intervals (CIs) individually. Hierarchical summary receiver operating characteristic curves (HSROCs) were used to summarize the pooled test performance, and the Grading of Recommendations, Assessment, Development and Evaluations criteria were used to appraise the quality of evidence.

Results

We identified 242 published relevant studies from 1,803 screened abstracts, of which 110 studies with 38,725 patients were included in this meta-analysis. Urinary NGAL/creatinine (diagnostic odds ratio [DOR] 16.2, 95% CI 10.1–25.9), urinary NGAL (DOR 13.8, 95% CI 10.2–18.8), and serum NGAL (DOR 12.6, 95% CI 9.3–17.3) had the best diagnostic accuracy for the risk of AKI. In subgroup analyses, urinary NGAL, urinary NGAL/creatinine, and serum NGAL had better diagnostic accuracy for AKI than urinary IL-18 in non-critically ill patients. However, all of the biomarkers had similar diagnostic accuracy in critically ill patients. In the setting of medical and non-sepsis patients, urinary NGAL had better predictive performance than urinary IL-18, urinary L-FABP, and urinary TIMP-2 × IGFBP-7: 0.3. In the surgical patients, urinary NGAL/creatinine and urinary KIM-1 had the best diagnostic accuracy. The HSROC values of urinary NGAL/creatinine, urinary NGAL, and serum NGAL were 91.4%, 85.2%, and 84.7%, respectively.

Conclusions

Biomarkers containing NGAL had the best predictive accuracy for the occurrence of AKI, regardless of whether or not the values were adjusted by urinary creatinine, and especially in medically treated patients. However, the predictive performance of urinary NGAL was limited in surgical patients, and urinary NGAL/creatinine seemed to be the most accurate biomarkers in these patients. All of the biomarkers had similar predictive performance in critically ill patients.

Trial registrationCRD42020207883, October 06, 2020.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-04223-6.

Advances in the study of subclinical AKI biomarkers

Acute kidney injury (AKI) is a prevalent and serious illness in all clinical departments, with a high morbidity and death rate, particularly in intensive care units, where prevention and treatment are crucial. As a result, active prevention, early detection, and timely intervention for acute kidney injury are critical. The current diagnostic criteria for acute kidney injury are an increase in serum creatinine concentration and/or a decrease in urine output, although creatinine and urine output merely reflect changes in kidney function, and AKI suggests injury or damage, but not necessarily dysfunction. The human kidney plays a crucial functional reserve role, and dysfunction is only visible when more than half of the renal mass is impaired. Tubular damage markers can be used to detect AKI before filtration function is lost, and new biomarkers have shown a new subset of AKI patients known as “subclinical AKI.” Furthermore, creatinine and urine volume are only marginally effective for detecting subclinical AKI. As a result, the search for new biomarkers not only identifies deterioration of renal function but also allows for the early detection of structural kidney damage. Several biomarkers have been identified and validated. This study discusses some of the most promising novel biomarkers of AKI, including CysC, NGAL, KIM-1, lL-18, L-FABP, IGFBP7, TIMP-2, Clusterin, and Penkid. We examine their performance in the diagnosis of subclinical AKI, limitations, and future clinical practice directions.

Point-of-Care (POC) Urinary L-Type Fatty Acid-Binding Protein (u-LFABP) Use in Critically Ill, Very Preterm Neonates

Preterm neonates are born with fewer functional nephrons, rendering them vulnerable to secondary insult. These insults are associated with acute kidney injury (AKI); thus, structural damage must be detected as early as possible. Urinary L-type fatty acid-binding protein (u-LFABP) has been proposed as a highly suitable kidney injury biomarker during prematurity. We aimed to analyze the use of POC u-LFABP in critically ill, very preterm neonates. This study was conducted at the neonatal intensive care unit (NICU), Dr. Cipto Mangunkusumo General Hospital, from November to December 2020. Baseline characteristics were recorded from electronic medical records. u-LFABP examination utilized stored urine samples from a previous study and was performed using a LFABP POC test kit. The proportion of abnormal u-LFABP (83.3%) was highest at 72 hours. Neonates with older gestational age (0–48 hours; $p=0.017$ ) and higher birth weight (0–48 hours; $p=0.022$ , 72 hours; $p=0.013$ ) had normal u-LFABP levels. Neonates exposed to nephrotoxic agents showed higher proportion of abnormal u-LFABP (0–48 hours; $p=0.006$ ). Longer invasive mechanical ventilation (IMV) period was observed in neonates with abnormal u-LFABP levels at 0–48 hours (7.44 ± 7.9 vs. 1.50 ± 2.9 days; $p=0.011$ ). We found an association between complication rates and poorer disease outcome trends with abnormal u-LFABP; however, this relationship was not supported statistically. In conclusion, this study demonstrated that u-LFABP can be detected using bedside POC kit in critically ill very preterm neonates and those exposed to nephrotoxic agents may be at risk for kidney injury, confirmed by abnormal u-LFABP levels.

Biomarkers for assessing acute kidney injury for people who are being considered for admission to critical care: a systematic review and cost-effectiveness analysis

BACKGROUND

Acute kidney injury is a serious complication that occurs in the context of an acute critical illness or during a postoperative period. Earlier detection of acute kidney injury may facilitate strategies to preserve renal function, prevent further disease progression and reduce mortality. Acute kidney injury diagnosis relies on a rise in serum creatinine levels and/or fall in urine output; however, creatinine is an imperfect marker of kidney function. There is interest in the performance of novel biomarkers used in conjunction with existing clinical assessment, such as NephroCheck^® (Astute Medical, Inc., San Diego, CA, USA), ARCHITECT^® urine neutrophil gelatinase-associated lipocalin (NGAL) (Abbott Laboratories, Abbott Park, IL, USA), and urine and plasma BioPorto NGAL (BioPorto Diagnostics A/S, Hellerup, Denmark) immunoassays. If reliable, these biomarkers may enable earlier identification of acute kidney injury and enhance management of those with a modifiable disease course.

OBJECTIVE

The objective was to evaluate the role of biomarkers for assessing acute kidney injury in critically ill patients who are considered for admission to critical care.

DATA SOURCES

Major electronic databases, conference abstracts and ongoing studies were searched up to June 2019, with no date restrictions. MEDLINE, EMBASE, Health Technology Assessment Database, Cumulative Index to Nursing and Allied Health Literature, Cochrane Central Register of Controlled Trials, Web of Science, World Health Organization Global Index Medicus, EU Clinical Trials Register, International Clinical Trials Registry Platform and ClinicalTrials.gov were searched.

REVIEW METHODS

A systematic review and meta-analysis were conducted to evaluate the performance of novel biomarkers for the detection of acute kidney injury and prediction of other relevant clinical outcomes. Random-effects models were adopted to combine evidence. A decision tree was developed to evaluate costs and quality-adjusted life-years accrued as a result of changes in short-term outcomes (up to 90 days), and a Markov model was used to extrapolate results over a lifetime time horizon.

RESULTS

A total of 56 studies (17,967 participants), mainly prospective cohort studies, were selected for inclusion. No studies addressing the clinical impact of the use of biomarkers on patient outcomes, compared with standard care, were identified. The main sources of bias across studies were a lack of information on blinding and the optimal threshold for NGAL. For prediction studies, the reporting of statistical details was limited. Although the meta-analyses results showed the potential ability of these biomarkers to detect and predict acute kidney injury, there were limited data to establish any causal link with longer-term health outcomes and there were considerable clinical differences across studies. Cost-effectiveness results were highly uncertain, largely speculative and should be interpreted with caution in the light of the limited evidence base. To illustrate the current uncertainty, 15 scenario analyses were undertaken. Incremental quality-adjusted life-years were very low across all scenarios, ranging from positive to negative increments. Incremental costs were also small, in general, with some scenarios generating cost savings with tests dominant over standard care (cost savings with quality-adjusted life-year gains). However, other scenarios generated results whereby the candidate tests were more costly with fewer quality-adjusted life-years, and were thus dominated by standard care. Therefore, it was not possible to determine a plausible base-case incremental cost-effectiveness ratio for the tests, compared with standard care.

LIMITATIONS

Clinical effectiveness and cost-effectiveness results were hampered by the considerable heterogeneity across identified studies. Economic model predictions should also be interpreted cautiously because of the unknown impact of NGAL-guided treatment, and uncertain causal links between changes in acute kidney injury status and changes in health outcomes.

CONCLUSIONS

Current evidence is insufficient to make a full appraisal of the role and economic value of these biomarkers and to determine whether or not they provide cost-effective improvements in the clinical outcomes of acute kidney injury patients.

FUTURE WORK

Future studies should evaluate the targeted use of biomarkers among specific patient populations and the clinical impact of their routine use on patient outcomes and management.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42019147039.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Evidence Synthesis programme and will be published in full in Health Technology Assessment; Vol. 26, No. 7. See the NIHR Journals Library website for further project information.

Urinary neutrophil gelatinase-associated lipocalin: Acute kidney injury in liver cirrhosis

Acute kidney injury (AKI) in liver cirrhosis is associated with poor clinical outcomes including an increased long and short-term mortality. The common type of AKI observed in patients with cirrhosis are prerenal AKI (PRA), hepatorenal syndrome (HRS) and acute tubular necrosis (ATN). Despite the growing knowledge and uniform definition for the diagnosis of AKI, there are several challenges including, early diagnosis and management. Precisely differentiating the type of AKI is critical, as therapies differ significantly. In this review, we summarize AKI in liver cirrhosis, their definition, pathophysiology and deficiencies of using the existing biomarker, serum creatinine. We outline the current clinical evidence on the novel biomarker urinary neutrophil gelatinase-associated lipocalin (uNGAL) and its potential role as a biomarker in the early detection, differentiation and prognostication of AKI. This review also briefly talks about other forthcoming biomarkers which hold promise in the management of AKI in liver cirrhosis.

Predictive value of novel biomarkers for chronic kidney disease among workers occupationally exposed to silica

There is a pressing need to find reliable biomarkers for the early diagnosis of silica-induced nephropathy. Abundant genes are upregulated in damaged kidneys with subsequent protein products appearing in the urine. Liver-type fatty acid-binding protein (L-FABP) and kidney injury molecule-1 (KIM-1) are among the most promising. Our objective was to study the importance of L-FABP and KIM-1 genes and their urinary proteins in the early detection of silica-induced renal injury, as compared with other conventional biomarkers. A cross-sectional study was conducted among 90 pottery workers occupationally exposed to silica, as compared to 90 controls. A full history taking and complete clinical examination were performed. Levels of serum creatinine, liver enzymes, urinary silicon, KIM-1, and L-FABP gene expression and protein products were measured. Estimated glomerular filtration rate (eGFR) was calculated, and abdominal ultrasound was performed. The results showed that the silica-exposed group had a statistically significant increase in serum creatinine and urinary silica, as well as a significant decrease in eGFR. Additionally, a significant increase in KIM-1 and L-FABP gene expression, associated with a significant increase in their urinary protein, was found among the exposed group. A positive correlation between urinary silica level and L-FABP gene expression was also found. A receiver operating characteristic curve analysis for L-FABP and KIM-1 gene as predictors for silica-induced nephropathy showed that L-FABP gene and protein specificity were greater than the KIM-1 gene and protein. Taken together, these findings suggest that the L-FABP gene and its protein product may be used as early indicators for renal injury among silica exposed workers.

Urinary Liver-Type Fatty-Acid-Binding Protein Predicts Long-Term Adverse Outcomes in Medical Cardiac Intensive Care Units

We prospectively investigated the prognostic value of urinary liver-type fatty-acid-binding protein (L-FABP) levels on hospital admission, both independently and in combination with serum creatinine-defined acute kidney injury (AKI), to predict long-term adverse outcomes in 1119 heterogeneous patients (mean age; 68 years) treated at medical (non-surgical) cardiac intensive care units (CICUs). Patients with stage 5 chronic kidney disease were excluded from the study. Of these patients, 47% had acute coronary syndrome and 38% had acute decompensated heart failure. The creatinine-defined AKI was diagnosed according to the "Kidney Disease: Improving Global Outcomes" criteria. The primary endpoint was a composite of all-cause death or progression to end-stage kidney disease, indicating the initiation of maintenance dialysis therapy or kidney transplantation. Creatinine-defined AKI occurred in 207 patients, with 44 patients having stage 2 or 3 disease. During a mean follow-up period of 41 months after enrollment, the primary endpoint occurred in 242 patients. Multivariate Cox regression analyses revealed L-FABP levels as independent predictors of the primary endpoint (p < 0.001). Adding L-FABP to a baseline model with established risk factors further enhanced reclassification and discrimination beyond that of the baseline model alone, for primary-endpoint prediction (both; p < 0.01). On Kaplan-Meier analyses, increased L-FABP (≥4th quintile value of 9.0 ng/mL) on admission or presence of creatinine-defined AKI, correlated with an increased risk of the primary endpoint (p < 0.001). Thus, urinary L-FABP levels on admission are potent and independent predictors of long-term adverse outcomes, and they might improve the long-term risk stratification of patients admitted at medical CICUs, when used in combination with creatinine-defined AKI.

Evaluation of urinary L-FABP as an early marker for diabetic nephropathy in type 2 diabetic patients

BACKGROUND

Albuminuria is the standard biomarker for the diagnosis of diabetic nephropathy (DN). However, some patients with persistent microalbuminuria still progress to chronic kidney disease, raising the question of finding a better biomarker. This study aimed to evaluate the correlation of urinary liver-type fatty acid-binding protein (L-FABP) levels with renal function and to compare the role of urinary albumin-to-creatinine ratio (ACR) with urinary L-FABP in early detection of DN in type 2 diabetic patients.

METHODS

The cross-sectional study was done on 106 type 2 diabetic patients and 30 non-diabetic people. L-FABP was measured with the Latex enhanced immunoturbidimetric technique.

RESULTS

There was a strong and negative correlation between the urine L-FABP levels and eGFR (r = -0.606, p<0.001). The urinary L-FABP levels were significantly higher (p<0.001) in the normoalbuminuria diabetic group than the non-diabetic control group. The ROC-curve analyses in the diabetic patients and the normoalbuminuria diabetic patients showed that the AUCL-FABP was remarkably higher (p<0.001) than the AUCACR. An optimal cutoff value of 5 mg L-FABP/g Cr (with the sensitivity of 98.1% and specificity of 90%) and of 4.3 mg L-FABP/g Cr (with the sensitivity of 100% and specificity of 86.67%) was set to detect DN in the diabetic patients and the normoalbuminuria diabetic patients, respectively.

CONCLUSIONS

The change in urinary L-FABP levels happened earlier than in urinary albumin during renal function impairment. Urinary L-FABP can be used as a better indicator than ACR for early detection of DN in type 2 diabetes.

The future for diagnostic tests of acute kidney injury in critical care: evidence synthesis, care pathway analysis and research prioritisation

BACKGROUND

Acute kidney injury (AKI) is highly prevalent in hospital inpatient populations, leading to significant mortality and morbidity, reduced quality of life and high short- and long-term health-care costs for the NHS. New diagnostic tests may offer an earlier diagnosis or improved care, but evidence of benefit to patients and of value to the NHS is required before national adoption.

OBJECTIVES

To evaluate the potential for AKI in vitro diagnostic tests to enhance the NHS care of patients admitted to the intensive care unit (ICU) and identify an efficient supporting research strategy.

DATA SOURCES

We searched ClinicalTrials.gov, The Cochrane Library databases, Embase, Health Management Information Consortium, International Clinical Trials Registry Platform, MEDLINE, metaRegister of Current Controlled Trials, PubMed and Web of Science databases from their inception dates until September 2014 (review 1), November 2015 (review 2) and July 2015 (economic model). Details of databases used for each review and coverage dates are listed in the main report.

REVIEW METHODS

The AKI-Diagnostics project included horizon scanning, systematic reviewing, meta-analysis of sensitivity and specificity, appraisal of analytical validity, care pathway analysis, model-based lifetime economic evaluation from a UK NHS perspective and value of information (VOI) analysis.

RESULTS

The horizon-scanning search identified 152 potential tests and biomarkers. Three tests, Nephrocheck^® (Astute Medical, Inc., San Diego, CA, USA), NGAL and cystatin C, were subjected to detailed review. The meta-analysis was limited by variable reporting standards, study quality and heterogeneity, but sensitivity was between 0.54 and 0.92 and specificity was between 0.49 and 0.95 depending on the test. A bespoke critical appraisal framework demonstrated that analytical validity was also poorly reported in many instances. In the economic model the incremental cost-effectiveness ratios ranged from £11,476 to £19,324 per quality-adjusted life-year (QALY), with a probability of cost-effectiveness between 48% and 54% when tests were compared with current standard care.

LIMITATIONS

The major limitation in the evidence on tests was the heterogeneity between studies in the definitions of AKI and the timing of testing.

CONCLUSIONS

Diagnostic tests for AKI in the ICU offer the potential to improve patient care and add value to the NHS, but cost-effectiveness remains highly uncertain. Further research should focus on the mechanisms by which a new test might change current care processes in the ICU and the subsequent cost and QALY implications. The VOI analysis suggested that further observational research to better define the prevalence of AKI developing in the ICU would be worthwhile. A formal randomised controlled trial of biomarker use linked to a standardised AKI care pathway is necessary to provide definitive evidence on whether or not adoption of tests by the NHS would be of value.

STUDY REGISTRATION

The systematic review within this study is registered as PROSPERO CRD42014013919.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

The Japanese clinical practice guideline for acute kidney injury 2016

Acute kidney injury (AKI) is a syndrome which has a broad range of etiologic factors depending on different clinical settings. Because AKI has significant impacts on prognosis in any clinical settings, early detection and intervention is necessary to improve the outcomes of AKI patients. This clinical guideline for AKI was developed by a multidisciplinary approach with nephrology, intensive care medicine, blood purification, and pediatrics. Of note, clinical practice for AKI management which was widely performed in Japan was also evaluated with comprehensive literature search.

The Japanese Clinical Practice Guideline for acute kidney injury 2016

Acute kidney injury (AKI) is a syndrome which has a broad range of etiologic factors depending on different clinical settings. Because AKI has significant impacts on prognosis in any clinical settings, early detection and intervention are necessary to improve the outcomes of AKI patients. This clinical guideline for AKI was developed by a multidisciplinary approach with nephrology, intensive care medicine, blood purification, and pediatrics. Of note, clinical practice for AKI management which was widely performed in Japan was also evaluated with comprehensive literature search.

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.

Current Metabolic Status Affects Urinary Liver-Type Fatty-Acid Binding Protein in Normoalbuminuric Patients With Type 2 Diabetes

Background

We aimed to study the association between urinary liver-type fatty acid-binding protein (L-FABP), a biomarker of tubulointerstitial injury, and the clinical characteristics of normoalbuminuric and albuminuric patients with type 2 diabetes in order to detect the factors affecting urinary L-FABP.

Methods

Urinary L-FABP levels were measured in 788 patients with type 2 diabetes and again in 666 patients at 6 months after the initial measurement. The association between the urinary L-FABP level and the clinical parameters was investigated in a retrospective cross-sectional study and a subsequent observation.

Results

The HbA1c (odds ratio (OR): 1.42; 95% confidence interval (CI): 1.11 - 1.79; P < 0.01), systolic blood pressure (OR: 1.03; 95% CI: 1.01 - 1.05; P < 0.01) levels and estimated glomerular filtration rate (OR: 0.98; 95% CI: 0.96 - 1.00; P = 0.01) were significantly associated with the high levels of urinary L-FABP (> 8.4 μg/gCr) in normoalbuminuric patients. However, a logistic regression analysis revealed that use of renin-angiotensin system (RAS) inhibitors (OR: 2.22; 95% CI: 1.16 - 4.89; P = 0.02), urinary albumin-to-creatinine ratio (ACR) (OR: 1.01; 95% CI: 1.00 - 1.01; P < 0.01) and serum HDL-cholesterol concentration (OR: 0.33; 95% CI: 0.11 - 0.89; P = 0.03) were significantly associated in albuminuric patients. In the follow-up observation, the change in urinary L-FABP was found to be significantly (P < 0.01) influenced by the change in the HbA1c level in both the normoalbuminuric and albuminuric patients.

Conclusions

High urinary L-FABP is associated with part of the current metabolic abnormalities, including high levels of HbA1c and systolic blood pressure among normoalbuminuric patients with type 2 diabetes.

Methodological issues in current practice may lead to bias in the development of biomarker combinations for predicting acute kidney injury

Individual biomarkers of renal injury are only modestly predictive of acute kidney injury (AKI). Using multiple biomarkers has the potential to improve predictive capacity. In this systematic review, statistical methods of articles developing biomarker combinations to predict acute kidney injury were assessed. We identified and described three potential sources of bias (resubstitution bias, model selection bias and bias due to center differences) that may compromise the development of biomarker combinations. Fifteen studies reported developing kidney injury biomarker combinations for the prediction of AKI after cardiac surgery (8 articles), in the intensive care unit (4 articles) or other settings (3 articles). All studies were susceptible to at least one source of bias and did not account for or acknowledge the bias. Inadequate reporting often hindered our assessment of the articles. We then evaluated, when possible (7 articles), the performance of published biomarker combinations in the TRIBE-AKI cardiac surgery cohort. Predictive performance was markedly attenuated in six out of seven cases. Thus, deficiencies in analysis and reporting are avoidable and care should be taken to provide accurate estimates of risk prediction model performance. Hence, rigorous design, analysis and reporting of biomarker combination studies are essential to realizing the promise of biomarkers in clinical practice.

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.

Detection of early renal injury in children with solid tumors undergoing chemotherapy by urinary neutrophil gelatinase-associated lipocalin

Acute kidney injury (AKI) is a complication in children with solid tumors undergoing chemotherapy, as it may prevent the use of therapy protocols and also hinder the supportive and diagnostic procedures. Thus, there is an urgent requirement for early predictive biomarkers of AKI. The most promising novel AKI biomarker is neutrophil gelatinase-associated lipocalin (NGAL). The aim of the present study was to compare the predictability of NGAL as a biomarker of AKI with creatinine as a traditional biomarker in children with solid tumors under chemotherapy. The study was performed on 30 patients with different types of solid tumors (reuroblastoma, Wilms tumor, medulloblastoma, rhabdomyosarcoma and Ewing sarcoma) and 20 control subjects. Urinary NGAL (uNGAL) and serum creatinine samples were taken three times: Baseline before the beginning of the treatment, one week after chemotherapy and at the end of the chemotherapy protocol. AKI is defined as a change in creatinine level by >50% of the baseline. The creatinine level only rises to this level in the third sample, while uNGAL increases significantly in the second and third samples with percentage of change 376.8 and 698.2%, respectively, which is highly significant (P<0.001). When comparing the predictive value of serum creatinine for AKI depending on the receiver operating characteristic curve with that of uNGAL, the area under the curve (AUC) for creatinine was 0.60 with a standard error (SE) of 0.086 and 95% confidence interval (CI) between 0.432 and 0.768, while that of uNGAL was highly predictive with an AUC of 0.847, SE 0.55 and 95% CI between 0.739 and 0.955. Depending only on the creatinine level for detecting the AKI will markedly delay the diagnosis; however, uNGAL is detected earlier, and is easier and more reliable as a marker for AKI in children with solid tumors undergoing chemotherapy.

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.

Expression of CX3CR1 in acute kidney injury associated with acute pancreatitis in rats

AIM: To investigate the expression of chemokine receptor CX3CR1 in acute kidney injury (AKI) associated with severe acute pancreatitis (SAP) in rats.

METHODS: Thirty male Sprague-Dawley rats were randomly divided into an SAP group, a mild acute pancreatitis (MAP) group and a sham operation (SO) group, with 10 rats in each group. SAP was induced in rats with 3.5% sodium taurocholate, while MAP was induced with 20% L-arginine. Histopathological changes in the pancreas and kidney tissues were examined under a light microscope. Serum amylase, creatinine and urea nitrogen levels were detected. Localization and expression of CX3CR1 in the kidney were determined by Western blot and immunohistochemical staining.

RESULTS: Compared with the MAP and SO groups, kidney histopathological score, levels of serum amylase, creatinine and urea nitrogen, as well as expression level of CX3CR1 in kidney tissue in the SAP group increased significantly (P < 0.05). Spearman's rank correlation analysis showed that expression of CX3CR1 was positively correlated with kidney histopathological score (r₁ = 0.878, P < 0.01). Pearson's correlation analysis showed that expression of CX3CR1 was positively correlated with serum creatinine and urea nitrogen levels (r₂ = 0.829, P < 0.01; r₃ = 0.78, P < 0.01).

CONCLUSION: Chemokine receptor CX3CR1 is involved in the process of SAP associated AKI, and its level can reflect the severity 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.

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.

Acute kidney injury following acute pancreatitis: A review

BACKROUND. Acute kidney injury (AKI) is a common serious complication of severe acute pancreatitis (SAP) and an important marker of morbidity and mortality in critically ill septic patients. AKI due to severe acute pancreatitis can be the result of hypoxemia, release of pancreatic amylase from the injured pancreas with impairment of renal microcirculation, decrease in renal perfusion pressure due to abdominal compartment syndrome, intraabdominal hypertension or hypovolemia. Endotoxins and reactive oxygen species (ROS) also play an important role in the pathophysiology of SAP and AKI. Knowledge of the pathophysiology and diagnosis of AKI following SAP might improve the therapeutic outcome of critically ill patients.

METHODS AND RESULTS

An overview of the pathophysiology, diagnosis and potential treatment options based on a literature search of clinical human and experimental studies from 1987 to 2013.

CONCLUSIONS

Early recognition of AKI and SAP in order to prevent severe complication like septic shock, intraabdominal hypertension or abdominal compartment syndrome leading to multiple organ dysfunction syndrome is a crucial tool of therapeutic measures in intensive care.