Postoperative biomarkers predict acute kidney injury and poor outcomes after pediatric cardiac surgery

Incorporation of biomarkers with the renal angina index for prediction of severe AKI in critically ill children

BACKGROUND AND OBJECTIVES

Novel AKI biomarkers carry variable performance for prediction of AKI in patients with heterogeneous illness. Until utility is demonstrated in critically ill patients outside of the cardiopulmonary bypass population, AKI biomarkers are unlikely to gain widespread implementation. Operationalization of an AKI risk stratification methodology, termed renal angina, was recently reported to enhance prediction at the time of intensive care unit admission for persistent severe AKI. The renal angina index (RAI) was developed to provide the clinical context to direct AKI biomarker testing. This study tested the hypothesis that incorporation of AKI biomarkers in patients fulfilling renal angina improves the prediction of persistent severe AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a multicenter study of 214 patients admitted to the pediatric intensive care unit with sepsis, the discrimination of plasma neutrophil gelatinase-associated lipocalin (NGAL), matrix metalloproteinase-8 (MMP-8), and neutrophil elastase-2 (Ela-2) were determined individually and in combination with the RAI for severe AKI. Net reclassification improvement (NRI) and integrated discrimination improvement (IDI) were calculated.

RESULTS

Individual biomarkers demonstrated marginal discrimination for severe AKI (area under curve [AUC]: NGAL, 0.72; MMP-8, 0.68; Ela-2, 0.72), inferior to prediction by the clinical model of the RAI (AUC=0.80). Incorporation of each biomarker significantly added to the renal angina model AKI prediction (AUC=0.80, increased to 0.84-0.88; P<0.05 for each). The inclusion of each biomarker with the RAI demonstrated NRI (0.512, 0.428, and 0.545 for NGAL, MMP-8, and Ela-2, respectively; all P<0.03) and IDI (0.075 for Ela-2). The inclusion of both Ela-2 and NGAL with RAI demonstrated an NRI of 0.871 (P<0.001) and an IDI of 0.1 (P=0.01).

CONCLUSIONS

This study shows that incorporation of AKI biomarkers into the RAI improves discrimination for severe AKI. The RAI optimizes the utility of AKI biomarkers in a heterogeneous, critically ill patient population.

Urinary kidney injury molecule 1 (KIM-1) and interleukin 18 (IL-18) as risk markers for heart failure in older adults: the Health, Aging, and Body Composition (Health ABC) Study

BACKGROUND

Kidney damage and reduced kidney function are potent risk factors for heart failure, but existing studies are limited to assessing albuminuria or estimated glomerular filtration rate (eGFR). We evaluated the associations of levels of urinary biomarkers of kidney tubular injury (interleukin 18 [IL-18] and kidney injury molecule 1 [KIM-1]) with future risk of heart failure.

STUDY DESIGN

Retrospective cohort study.

SETTING & PARTICIPANTS

2,917 participants without heart failure in the Health, Aging, and Body Composition (Health ABC) cohort.

PREDICTORS

Ratios of urine KIM-1, IL-18, and albumin to creatinine (KIM-1:Cr, IL-18:Cr, and ACR, respectively).

OUTCOMES

Incident heart failure over a median follow-up of 12 years.

RESULTS

Median values of each marker at baseline were 812 (IQR, 497-1,235)pg/mg for KIM-1:Cr, 31 (IQR, 19-56)pg/mg for IL-18:Cr, and 8 (IQR, 5-19) mg/g for ACR. 596 persons developed heart failure during follow-up. The top quartile of KIM-1:Cr was associated with risk of incident heart failure after adjustment for baseline eGFR, heart failure risk factors, and ACR (HR, 1.32; 95% CI, 1.02-1.70) in adjusted multivariate proportional hazards models. The top quartile of IL-18:Cr also was associated with heart failure in a model adjusted for risk factors and eGFR (HR, 1.35; 95% CI, 1.05-1.73), but was attenuated by adjustment for ACR (HR, 1.15; 95% CI, 0.89-1.48). The top quartile of ACR had a stronger adjusted association with heart failure (HR, 1.96; 95% CI, 1.53-2.51).

LIMITATIONS

Generalizability to other populations is uncertain.

CONCLUSIONS

Higher urine KIM-1 concentrations were associated independently with incident heart failure risk, although the associations of higher ACR were of stronger magnitude.

Acute kidney injury in neonates: from urine output to new biomarkers

In the past 10 years, great effort has been made to define and classify a common syndrome previously known as acute renal failure and now renamed “acute kidney injury (AKI).” Initially suggested and validated in adult populations, AKI classification was adapted to the pediatric population and recently has been modified for the neonatal population. Several studies have been performed in adults and older children using this consensus definition, leading to improvement in the knowledge of AKI incidence and epidemiology. In spite of these advances, the peculiar renal pathophysiology of critically ill newborn patients makes it difficult to interpret urine output (UO) and serum creatinine (SCr) levels in these patients to diagnose AKI. Also, new urine biomarkers have emerged as a possible alternative to diagnose early AKI in the neonatal population. In this review, we describe recent advances in neonatal AKI epidemiology, discuss difficulties in diagnosing AKI in newborns, and show recent advances in new AKI biomarkers and possible long-term consequences after AKI episode.

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.

Proteomics in acute kidney injury--current status and future promise

Pediatric acute kidney injury (AKI) is associated with increased morbidity, mortality and associated healthcare costs. Unfortunately, there are currently no effective therapies available, and this has been attributed in part to the late diagnosis of AKI. Therefore, significant efforts have been made to develop early diagnostic tools for AKI in the hope that early identification of renal injury will allow for effective therapeutic intervention. Different transcriptomic, proteomic and metabolomic technologies offer unbiased approaches to identifying novel biomarkers of AKI. This review will provide an overview of non-invasive pediatric AKI biomarkers. It will focus on unbiased technologies by using examples of biomarkers identified with "-omic" technologies and different methodological and implementation challenges will be highlighted. Finally, emerging proteomic techniques that may be applicable to biomarker discovery will be presented. Ultimately, the development of novel biomarkers of AKI may lead to the early diagnosis and effective therapeutic intervention of AKI to improve patient outcomes.

Postoperative neutrophil gelatinase-associated lipocalin predicts acute kidney injury after pediatric cardiac surgery*

OBJECTIVE

We investigated the temporal pattern and predictive value of neutrophil gelatinase-associated lipocalin for early identification of acute kidney injury in children undergoing cardiac surgery.

DESIGN

Prospective observational cohort study.

SETTING

One PICU in a tertiary medical center in Madrid, Spain.

PATIENTS

One hundred six children older than 15 days and younger than 16 years undergoing surgery for congenital cardiac lesions.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Urine samples were obtained before and at intervals after surgery. Acute kidney injury was defined according to pediatric Risk, Injury, Failure, Loss, and End-stage kidney disease criteria. The temporal pattern of both urine neutrophil gelatinase-associated lipocalin absolute concentration elevation and normalized to urine creatinine concentration was correlated with the development of acute kidney injury and other clinical outcomes. We evaluated the predictive ability of both urine neutrophil gelatinase-associated lipocalin and urine neutrophil gelatinase-associated lipocalin/creatinine by area under the curve, when added to a clinical predictive model. Data from 106 pediatric patients were analyzed. Acute kidney injury occurred in 42 patients (39.6%). Urine neutrophil gelatinase-associated lipocalin significantly increased in patients with acute kidney injury at 1, 3, and 15 hours postoperatively. Urine neutrophil gelatinase-associated lipocalin and urine neutrophil gelatinase-associated lipocalin/creatinine correlated with surgical variables and clinical outcomes. Acute kidney injury prediction improved when urine neutrophil gelatinase-associated lipocalin was added to a clinical model (area under the curve increased at 1 hr from 0.85 to 0.91 and at 3 hr to 0.92). Neither the urine neutrophil gelatinase-associated lipocalin nor the urine neutrophil gelatinase-associated lipocalin/creatinine values were significantly different between patients with prerenal and sustained acute kidney injury.

CONCLUSIONS

Urine neutrophil gelatinase-associated lipocalin is a predictive biomarker for acute kidney injury after pediatric cardiac surgery, and it may permit earlier intervention that improves outcome of acute kidney injury. Urine neutrophil gelatinase-associated lipocalin normalized to urine creatinine improves the prediction of acute kidney injury severity but offers no advantage in acute kidney injury diagnosis.

Serum and urinary NGAL in septic newborns

Neutrophil gelatinase-associated lipocalin (NGAL) is postulated to be a potentially new and highly specific/sensitive marker of acute kidney injury (AKI). The aim of this study was to assess the impact of inflammation on serum and urine NGAL in newborns that were treated due to infection. We determined serum and urine NGAL concentrations in 73 infants (51 with sepsis; 22 with severe sepsis) admitted to the Intensive Care Unit in the first month of life, for three consecutive days during the course of treatment for infection. 29 neonates without infection served as the control group. Septic patients, in particular, severe sepsis patients, had increased serum and urinary NGAL levels in the three subsequent days of observation. Five septic patients who developed AKI had elevated serum and urinary NGAL values to a similar extent as septic neonates without AKI. A strong correlation was found between the concentration of serum and urinary NGAL and inflammatory markers, such as CRP and procalcitonin. Serum and urinary NGAL levels were also significantly associated with NTISS (neonatal therapeutic intervention scoring system) values. We conclude that increased serum and urinary NGAL values are not solely a marker of AKI, and more accurately reflect the severity of inflammatory status.

Acute kidney injury-epidemiology, outcomes and economics

Acute kidney injury (AKI) is a widespread problem of epidemic status. Compelling evidence indicates that the incidence of AKI is rapidly increasing, particularly among hospitalized patients with acute illness and those undergoing major surgery. This increase might be partially attributable to greater recognition of AKI, improved ascertainment in administrative data and greater sensitivity of consensus diagnostic and classification schemes. Other causes could be an ageing population, increasing incidences of cardiovascular disease, diabetes mellitus and chronic kidney disease (CKD), and an expanding characterization of modifiable risk factors, such as sepsis, administration of contrast media and exposure to nephrotoxins. The sequelae of AKI are severe and characterized by increased risk of short-term and long-term mortality, incident CKD and accelerated progression to end-stage renal disease. AKI-associated mortality is decreasing, but remains unacceptably high. Moreover, the absolute number of patients dying as a result of AKI is increasing as the incidence of the disorder increases, and few proven effective preventative or therapeutic interventions exist. Survivors of AKI, particularly those who remain on renal replacement therapy, often have reduced quality of life and consume substantially greater health-care resources than the general population as a result of longer hospitalizations, unplanned intensive care unit admissions and rehospitalizations.

Neutrophil gelatinase associated lipocalin in acute kidney injury

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Near-infrared spectroscopy: exposing the dark (venous) side of the circulation

The safety of anesthesia has improved greatly in the past three decades. Standard perioperative monitoring, including pulse oximetry, has practically eliminated unrecognized arterial hypoxia as a cause for perioperative injury. However, most anesthesia-related cardiac arrests in children are now cardiovascular in origin, and standard monitoring is unable to detect many circulatory abnormalities. Near-infrared spectroscopy provides noninvasive continuous access to the venous side of regional circulations that can approximate organ-specific and global measures to facilitate the detection of circulatory abnormalities and drive goal-directed interventions to reduce end-organ ischemic injury.

Urinary biomarkers of AKI and mortality 3 years after cardiac surgery

Urinary biomarkers of AKI provide prognostic value for in-hospital outcomes, but little is known about their association with longer-term mortality after surgery. We sought to assess the association between kidney injury biomarkers and all-cause mortality in an international, multicenter, prospective long-term follow-up study from six clinical centers in the United States and Canada composed of 1199 adults who underwent cardiac surgery between 2007 and 2009 and were enrolled in the Translational Research in Biomarker Endpoints in AKI cohort. On postoperative days 1-3, we measured the following five urinary biomarkers: neutrophil gelatinase-associated lipocalin, IL-18, kidney injury molecule-1 (KIM-1), liver fatty acid binding protein, and albumin. During a median follow-up of 3.0 years (interquartile range, 2.2-3.6 years), 139 participants died (55 deaths per 1000 person-years). Among patients with clinical AKI, the highest tertiles of peak urinary neutrophil gelatinase-associated lipocalin, IL-18, KIM-1, liver fatty acid binding protein, and albumin associated independently with a 2.0- to 3.2-fold increased risk for mortality compared with the lowest tertiles. In patients without clinical AKI, the highest tertiles of peak IL-18 and KIM-1 also associated independently with long-term mortality (adjusted hazard ratios [95% confidence intervals] of 1.2 [1.0 to 1.5] and 1.8 [1.4 to 2.3] for IL-18 and KIM-1, respectively), and yielded continuous net reclassification improvements of 0.26 and 0.37, respectively, for the prediction of 3-year mortality. In conclusion, urinary biomarkers of kidney injury, particularly IL-18 and KIM-1, in the immediate postoperative period provide additional prognostic information for 3-year mortality risk in patients with and without clinical AKI.

Procalcitonin levels predict acute kidney injury and prognosis in acute pancreatitis: a prospective study

Background

Acute kidney injury (AKI) has been proposed as a leading cause of mortality for acute pancreatitis (AP) patients admitted to the intensive care unit (ICU). This study investigated the predictive value of procalcitonin (PCT) for AKI development and relevant prognosis in patients with AP, and compared PCT’s predictive power with that of other inflammation-related variables.

Methods

Between January 2011 and March 2013, we enrolled 305 cases with acute pancreatitis admitted to ICU. Serum levels of PCT, serum amyloid A (SAA), interleukin-6 (IL-6), and C reactive protein (CRP) were determined on admission. Serum PCT was tested in patients who developed AKI on the day of AKI occurrence and on either day 28 after occurrence (for survivors) or on the day of death (for those who died within 28 days).

Results

Serum PCT levels were 100-fold higher in the AKI group than in the non-AKI group on the day of ICU admission (p<0.05). The area under the receiver-operating characteristic (ROC) curve of PCT for predicting AKI was 0.986, which was superior to SAA, CRP, and IL-6 (p<0.05). ROC analysis revealed all variables tested had lower predictive performance for AKI prognosis. The average serum PCT level on day 28 (2.67 (0.89, 7.99) ng/ml) was significantly (p<0.0001) lower than on the day of AKI occurrence (43.71 (19.24,65.69) ng/ml) in survivors, but the serum PCT level on death (63.73 (34.22,94.30) ng/ml) was higher than on the day of AKI occurrence (37.55 (18.70,74.12) ng/ml) in non-survivors, although there was no significant difference between the two days in the latter group (p = 0.1365).

Conclusion

Serum PCT is superior to CRP, IL-6, and SAA for predicting the development of AKI in patients with AP, and also can be used for dynamic evaluation of AKI prognosis.

Predictive performance of urine neutrophil gelatinase-associated lipocalin for dialysis requirement and death following cardiac surgery in neonates and infants

BACKGROUND AND OBJECTIVES

Urine neutrophil gelatinase-associated lipocalin (uNGAL) has been shown to accurately predict and allow early detection of AKI, as assessed by an increase in serum creatinine in children and adults. The present study explores the accuracy of uNGAL for the prediction of severe AKI-related outcomes in neonates and infants undergoing cardiac surgery: dialysis requirement and/or death within 30 days.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Prospective, observational cohort study conducted in a tertiary referral pediatric cardiac intensive care unit, including 75 neonates and 125 infants undergoing surgery with cardiopulmonary bypass between August 1, 2010, and May 31, 2011. Urine samples were collected before surgery and at median of five time points within 48 hours of bypass. Urine NGAL was quantified as absolute concentration, creatinine-normalized concentration, and absolute excretion rate, and a clusterization algorithm was applied to the individual uNGAL kinetics. The accuracy for the prediction of the outcome was assessed using receiver-operating characteristic areas, likelihood ratios, diagnostic odds ratios, net reclassification index, integrated reclassification improvement, and number needed to screen.

RESULTS

A total of 1176 urine samples were collected. Of all patients, 8% required dialysis and 4% died. Three clusters of uNGAL kinetics were identified, including patients with significantly different outcomes. The uNGAL level peaked between 1 and 3 hours of bypass and remained high in half of all patients who required dialysis or died. The uNGAL levels measured within 24 hours of bypass accurately predicted the outcome and performed best after normalization to creatinine, with varying cutoffs according to the time elapsed since bypass. The number needed to screen to correctly identify the risk of dialysis or death in one patient varied between 1.5 and 2.6 within 12 hours of bypass.

CONCLUSIONS

uNGAL is a valuable predictive tool of dialysis requirement and death in neonates and infants with AKI after cardiac surgery.

Nanosized contrast agents to noninvasively detect kidney inflammation by magnetic resonance imaging

Several molecular imaging methods have been developed that use nanosized contrast agents to detect markers of inflammation within tissues. Kidney inflammation contributes to disease progression in a wide range of autoimmune and inflammatory diseases, and a biopsy is currently the only method of definitively diagnosing active kidney inflammation. However, the development of new molecular imaging methods that use contrast agents capable of detecting particular immune cells or protein biomarkers will allow clinicians to evaluate inflammation throughout the kidneys and to assess a patient's response to immunomodulatory drugs. These imaging tools will improve our ability to validate new therapies and to optimize the treatment of individual patients with existing therapies. This review describes the clinical need for new methods of monitoring kidney inflammation and recent advances in the development of nanosized contrast agents for the detection of inflammatory markers of kidney disease.

Urinary biomarkers and renal near-infrared spectroscopy predict intensive care unit outcomes after cardiac surgery in infants younger than 6 months of age

OBJECTIVE

To assess the ability of urinary acute kidney injury biomarkers and renal near-infrared spectroscopy (NIRS) to predict outcomes in infants after surgery for congenital heart disease.

METHODS

Urinary levels of neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18 (IL-18), kidney injury molecule-1 (KIM-1), and cystatin C were measured preoperatively and postoperatively in 49 infants younger than 6 months of age. Renal NIRS was monitored for the first 24 hours after surgery. A composite poor outcome was defined as death, the need for renal replacement therapy, prolonged time to first extubation, or prolonged intensive care unit length of stay.

RESULTS

Forty-two (86%) patients had acute kidney injury as indicated by at least Acute Kidney Injury Network/Kidney Disease: Improving Global Outcomes (AKIN/KDIGO) stage 1 criteria, and 17 (35%) patients had poor outcomes, including 3 deaths. With the exception of KIM-1, all biomarkers demonstrated significant increases within 24 hours postoperatively among patients with poor outcomes. Low levels of NGAL and IL-18 demonstrated high negative predictive values (91%) within 2 hours postoperatively. Poor outcome infants had greater cumulative time with NIRS saturations less than 50% (60 vs 1.5 minutes; P = .02) in the first 24 hours.

CONCLUSIONS

Within the first 24 hours after cardiopulmonary bypass, infants at increased risk for poor outcomes demonstrated elevated urinary NGAL, IL-18, and cystatin C and increased time with low NIRS saturations. These findings suggest that urinary biomarkers and renal NIRS may differentiate patients with good versus poor outcomes in the early postoperative period, which could assist clinicians when counseling families and inform the development of future clinical trials.

Preoperative prediction of acute kidney injury--from clinical scores to biomarkers

Early acute kidney injury (AKI) diagnosis in critically ill children has been an important recent research focus because of the known association of AKI with poor outcomes and the requirement of early intervention to mitigate negative effects of AKI. In children having surgery, the preoperative period offers a unique opportunity to predict postoperative acute kidney injury (AKI), well before AKI occurs. Pediatric AKI epidemiologic studies have begun to identify which preoperative factors may predict development of postoperative cardiac surgery. Using these clinical risk factors, it may be possible to derive preoperative clinical risk scores and improve upon our ability to risk-stratify children into AKI treatment trials, pre-emptively provide conservative renal injury prevention strategies, and ultimately improve patient outcomes. Developing risk scores requires rigorous methodology and validation before widespread use. There is little information currently on the use of preoperative biological or physiological biomarkers to predict postoperative AKI, representing an important area of future research. This review will provide an overview of methodology of preoperative risk score development, discuss pediatric-specific issues around deriving such risk scores, including the combination of preoperative clinical and biologic biomarkers for AKI prediction, and suggest future research avenues.

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.

Estimating the receiver operating characteristic curve in studies that match controls to cases on covariates

RATIONALE AND OBJECTIVES

Studies evaluating a new diagnostic imaging test may select control subjects without disease who are similar to case subjects with disease in regard to factors potentially related to the imaging result. Selecting one or more controls that are matched to each case on factors such as age, comorbidities, or study site improves study validity by eliminating potential biases due to differential characteristics of readings for cases versus controls. However, it is not widely appreciated that valid analysis requires that the receiver operating characteristic (ROC) curve be adjusted for covariates. We propose a new computationally simple method for estimating the covariate-adjusted ROC curve that is appropriate in matched case-control studies.

MATERIALS AND METHODS

We provide theoretical arguments for the validity of the estimator and demonstrate its application to data. We compare the statistical properties of the estimator with those of a previously proposed estimator of the covariate-adjusted ROC curve. We demonstrate an application of the estimator to data derived from a study of emergency medical services encounters where the goal is to diagnose critical illness in nontrauma, non-cardiac arrest patients. A novel bootstrap method is proposed for calculating confidence intervals.

RESULTS

The new estimator is computationally very simple, yet we show it yields values that approximate the existing, more complicated estimator in simulated data sets. We found that the new estimator has excellent statistical properties, with bias and efficiency comparable with the existing method.

CONCLUSIONS

In matched case-control studies, the ROC curve should be adjusted for matching covariates and can be estimated with the new computationally simple approach.

Cardiorenal [corrected] syndrome: an emerging problem in pediatric critical care

The cardiorenal syndrome (CRS) refers to a complex pathophysiologic state in which heart and kidney dysfunction coexist. Although a robust amount of adult literature exists, limited reports have been made regarding CRS in pediatric patients. However, CRS is increasingly being recognized as an impactful clinical problem that can have important implications regarding the need for treatment and prognosis. Although wide acceptance of a unified definition of CRS is lacking, a general consensus exists that CRS can be either primarily caused by cardiac disease with secondary effects on the kidney, or vice versa, as well as systemic conditions in which cardiac and renal disease are both considered to be secondary. Convincing data in the pediatric perioperative population have been reported, but there is a paucity of information in acute and chronic heart failure (HF), as well as acute kidney injury (AKI) and chronic kidney disease (CKD). Herein, we briefly report on the adult literature and summarize the current pediatric experience.

Urinary biomarkers and acute kidney injury in children: the long road to clinical application

Pediatric acute kidney injury is rising with the advances in technology available for children with chronic conditions or those who are critically ill. Serum creatinine and urine output, traditional markers of renal function, often allow only delayed and unreliable diagnosis of acute kidney injury. Biomarker development in pediatric patients with low disease prevalence is challenging (small cohorts, few analyzable events). In this issue of Pediatric Nephrology, Ivanisevic and colleagues report that urinary liver-type fatty-acid-binding protein (L-FABP) can be used for early identification of pediatric acute kidney injury in a small cohort undergoing cardiac surgery. Addition of the biomarker resulted in an improvement in early diagnosis compared with a clinical model (age, gender, body weight, cardiopulmonary bypass duration, and aortic clamp time). It is noteworthy that the preoperative clinical model performed excellently in predicting postsurgery pediatric acute kidney injury. Further work is needed before this or other novel biomarkers (alone or in combination) can be implemented in clinical practice. Large-scale observational studies are needed to test these biomarkers against hard clinical endpoints, independent of serial measurements of serum creatinine concentrations. Prospective randomized interventional trials using exclusively high biomarker levels to define acute kidney injury should demonstrate improved clinical outcomes.

Acute kidney injury after cardiovascular surgery: an overview

Acute kidney injury is a complication of open-heart surgery that carries a poor prognosis. Studies have shown that postoperative renal function deterioration in cardiovascular surgery patients increases in-hospital mortality and adversely affects long-term survival. Identifying individuals at risk for developing AKI and aggressive early intervention is extremely important to optimize outcomes. This paper provides an overview of the etiology, prognostic markers, risk factors, and prevention of AKI and treatments that may favorably affect outcomes.

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.

Intratracheal IL-6 protects against lung inflammation in direct, but not indirect, causes of acute lung injury in mice

Introduction

Serum and bronchoalveolar fluid IL-6 are increased in patients with acute respiratory distress syndrome (ARDS) and predict prolonged mechanical ventilation and poor outcomes, although the role of intra-alveolar IL-6 in indirect lung injury is unknown. We investigated the role of endogenous and exogenous intra-alveolar IL-6 in AKI-mediated lung injury (indirect lung injury), intraperitoneal (IP) endotoxin administration (indirect lung injury) and, for comparison, intratracheal (IT) endotoxin administration (direct lung injury) with the hypothesis that IL-6 would exert a pro-inflammatory effect in these causes of acute lung inflammation.

Methods

Bronchoalveolar cytokines (IL-6, CXCL1, TNF-α, IL-1β, and IL-10), BAL fluid neutrophils, lung inflammation (lung cytokines, MPO activity [a biochemical marker of neutrophil infiltration]), and serum cytokines were determined in adult male C57Bl/6 mice with no intervention or 4 hours after ischemic AKI (22 minutes of renal pedicle clamping), IP endotoxin (10 µg), or IT endotoxin (80 µg) with and without intratracheal (IT) IL-6 (25 ng or 200 ng) treatment.

Results

Lung inflammation was similar after AKI, IP endotoxin, and IT endotoxin. BAL fluid IL-6 was markedly increased after IT endotoxin, and not increased after AKI or IP endotoxin. Unexpectedly, IT IL-6 exerted an anti-inflammatory effect in healthy mice characterized by reduced BAL fluid cytokines. IT IL-6 also exerted an anti-inflammatory effect in IT endotoxin characterized by reduced BAL fluid cytokines and lung inflammation; IT IL-6 had no effect on lung inflammation in AKI or IP endotoxin.

Conclusion

IL-6 exerts an anti-inflammatory effect in direct lung injury from IT endotoxin, yet has no role in the pathogenesis or treatment of indirect lung injury from AKI or IP endotoxin. Since intra-alveolar inflammation is important in the pathogenesis of direct, but not indirect, causes of lung inflammation, IT anti-inflammatory treatments may have a role in direct, but not indirect, causes of ARDS.

Neonatal RIFLE

A standardized classification of acute kidney injury (AKI) has recently been proposed with the RIFLE (Risk, Injury, Failure, Loss of function, End-stage kidney disease) score. Such definition/classification has been applied both in adult and in paediatric patients. Neonatal definition of AKI likely results as a challenging task due to the peculiar renal pathophysiology of newborn critically ill patients. Their so-called 'immature kidneys' require careful management and neonatal AKI is frequently complicated by unfavourable outcomes. A recent attempt to implement the RIFLE score with a neonatal modification might lead to improvement on the knowledge of AKI incidence and epidemiology.

Linking injury to outcome in acute kidney injury: a matter of sensitivity

Current consensus definitions of Acute Kidney Injury (AKI) utilise thresholds of change in serum or plasma creatinine and urine output. Biomarkers of renal injury have been validated against these definitions. These biomarkers have also been shown to be independently associated with mortality and need for dialysis. For AKI definitions to include these structural biomarkers, there is a need for an independent outcome against which to judge both markers of functional change and structural markers of injury. We illustrate how sensitivity to need for dialysis and death can be used to link functional and structural (biomarker) based definitions of AKI. We demonstrated the methodology in a representative cohort of critically ill patients, in which an increase of plasma creatinine of >26.4 µmol/L in 48 hours or >50% in 7 days (Functional-AKI) had a sensitivity of 62% for death or dialysis within 30 days. In a development sub-cohort the urinary neutrophil-gelatinase-associated-lipocalin threshold with a 62% sensitivity for death or dialysis was 140 ng/ml (Structural-AKI). Using these thresholds in a validation sub-cohort, the risk of death or dialysis relative to those with no AKI by either definition was, for combined Structural-AKI and Functional-AKI 3.11 (95% Confidence interval: 2.53 to 3.55), for those with Structural-AKI but not Functional-AKI 1.51 (1.26 to 1.62), and for those with Functional-AKI but not Structural-AKI 1.34 (1.16 to 1.42). Linking functional and structural biomarkers via sensitivity for death and dialysis is a viable method by which to define thresholds for novel biomarkers of AKI.

Performance of kidney injury molecule-1 and liver fatty acid-binding protein and combined biomarkers of AKI after cardiac surgery

BACKGROUND AND OBJECTIVES

AKI is common and novel biomarkers may help provide earlier diagnosis and prognosis of AKI in the postoperative period.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was a prospective, multicenter cohort study involving 1219 adults and 311 children consecutively enrolled at eight academic medical centers. Performance of two urine biomarkers, kidney injury molecule-1 (KIM-1) and liver fatty acid-binding protein (L-FABP), alone or in combination with other injury biomarkers during the perioperative period was evaluated. AKI was defined as doubling of serum creatinine or need for acute dialysis.

RESULTS

KIM-1 peaked 2 days after surgery in adults and 1 day after surgery in children, whereas L-FABP peaked within 6 hours after surgery in both age groups. In multivariable analyses, the highest quintile of the first postoperative KIM-1 level was associated with AKI compared with the lowest quintile in adults, whereas the first postoperative L-FABP was not associated with AKI. Both KIM-1 and L-FABP were not significantly associated with AKI in adults or children after adjusting for other kidney injury biomarkers (neutrophil gelatinase-associated lipocalin and IL-18). The highest area under the curves achievable for discrimination for AKI were 0.78 in adults using urine KIM-1 from 6 to 12 hours, urine IL-18 from day 2, and plasma neutrophil gelatinase-associated lipocalin from day 2 and 0.78 in children using urine IL-18 from 0 to 6 hours and urine L-FABP from day 2.

CONCLUSIONS

Postoperative elevations of KIM-1 associate with AKI and adverse outcmes in adults but were not independent of other AKI biomarkers. A panel of multiple biomarkers provided moderate discrimination for AKI.

Preoperative endogenous ouabain predicts acute kidney injury in cardiac surgery patients

OBJECTIVES

Acute kidney injury is a frequent complication of cardiac surgery and increases morbidity and mortality. As preoperative biomarkers predicting the development of acute kidney injury are not available, we have tested the hypothesis that preoperative plasma levels of endogenous ouabain may function as this type of biomarker.

RATIONALE AND DESIGN

Endogenous ouabain is an adrenal stress hormone associated with adverse cardiovascular outcomes. Its involvement in acute kidney injury is unknown. With studies in patients and animal settings, including isolated podocytes, we tested the above mentioned hypothesis.

PATIENTS

Preoperative endogenous ouabain was measured in 407 patients admitted for elective cardiac surgery and in a validation population of 219 other patients. We also studied the effect of prolonged elevations of circulating exogenous ouabain on renal parameters in rats and the influence of ouabain on podocyte proteins both "in vivo" and "in vitro."

MAIN RESULTS

In the first group of patients, acute kidney injury (2.8%, 8.3%, 20.3%, p < 0.001) and ICU stay (1.4±0.38, 1.7±0.41, 2.4±0.59 days, p = 0.014) increased with each incremental preoperative endogenous ouabain tertile. In a linear regression analysis, the circulating endogenous ouabain value before surgery was the strongest predictor of acute kidney injury. In the validation cohort, acute kidney injury (0%, 5.9%, 8.2%, p < 0.0001) and ICU stay (1.2±0.09, 1.4±0.23, 2.2±0.77 days, p = 0.003) increased with the preoperative endogenous ouabain tertile. Values for preoperative endogenous ouabain significantly improved (area under curve: 0.85) risk prediction over the clinical score alone as measured by integrate discrimination improvement and net reclassification improvement. Finally, in the rat model, elevated circulating ouabain reduced creatinine clearance (-18%, p < 0.05), increased urinary protein excretion (+ 54%, p < 0.05), and reduced expression of podocyte nephrin (-29%, p < 0.01). This last finding was replicated ex vivo by incubating podocyte primary cell cultures with low-dose ouabain.

CONCLUSIONS

Preoperative plasma endogenous ouabain levels are powerful biomarkers of acute kidney injury and postoperative complications and may be a direct cause of podocyte damage.

Neutrophil gelatinase-associated lipocalin: pathophysiology and clinical applications

Neutrophil gelatinase-associated lipocalin (NGAL), a 25 kDa protein produced by injured nephron epithelia, is one of the most promising new markers of renal epithelial injury. In contrast to serum creatinine and urinary output, which are the measures of kidney function, NGAL is specifically induced in the damaged nephron and then released into blood and urine, where it can be readily measured. Careful proof-of-concept studies using defined animal models have uncovered the sources and trafficking of NGAL in acute kidney injury (AKI) and have addressed the contributions of renal and non-renal sources. Clinical studies indicate that NGAL, unlike creatinine, is a marker responsive to tissue stress and nephron injury, but less so to adaptive hemodynamic responses. In certain clinical settings, NGAL is an earlier marker compared with serum creatinine. In addition, clinical studies have shown that NGAL is a powerful predictor of poor clinical outcomes, which can be used to risk stratify patients when combined with serum creatinine. NGAL has important limitations, including its responsiveness in systemic inflammation, which is partially uncoupled from its response to kidney injury and which needs to be considered when interpreting NGAL results clinically. This review covers the biology and pathophysiology of NGAL and summarizes the results of the growing body of clinical studies that have addressed the utility of NGAL in the early diagnosis of AKI, in the distinction of intrinsic AKI and in the prognostic assessment of broad patient populations.

Clinical utility of biomarkers of AKI in cardiac surgery and critical illness

AKI is a common and serious complication that is associated with several adverse outcomes in hospitalized patients. The past several years have seen a large number of multicenter investigations of biomarkers of AKI in the setting of cardiac surgery and critical illness. This review summarizes these biomarker results to identify applications for clinical use. The Translational Research Investigating Biomarker Endpoints in AKI (TRIBE-AKI) study showed that blood and urine biomarkers measured preoperatively, immediately postoperatively, and at the time of the clinical increase in serum creatinine in the setting of cardiac surgery all had the ability to improve patient risk stratification for a variety of important clinical end points. Analyses of biomarkers concentrations from the Acute Respiratory Distress Syndrome Network, EARLY ARF, and other studies of critically ill subjects have similarly shown that biomarkers measured early in the clinical course can forecast the development of AKI and need for renal replacement therapy as well as inpatient mortality. Although biomarkers have informed the diagnosis, prognosis, and treatment of AKI and are inching closer to clinical application, large multicenter interventional clinical trials to prevent AKI using biomarkers should continue to be an active area of clinical investigation.

Pediatric Acute Kidney Injury: Different From Acute Renal Failure But How And Why

Acute kidney injury [AKI] refers to a clinical syndrome encompassing various etiologies and occurring in a variety of clinical settings, with manifestations ranging from subtle biochemical and structural changes, to minimal elevation in serum creatinine, to anuric renal failure. Understanding the spectrum of AKI and the importance of the early pre-clinical damage stage has resulted in an improved ability to define and stage pediatric AKI, to understand the AKI-to-CKD transition, and harness novel damage biomarkers to predict AKI and its adverse outcomes. These concepts are expanded upon in this review, with an emphasis on publications from the past three years.

Urine IL-18, NGAL, IL-8 and serum IL-8 are biomarkers of acute kidney injury following liver transplantation

BACKGROUND

AKI is common following liver transplantation and is associated with significant morbidity and mortality. Biomarkers of AKI have not been well established in this setting but are needed to help guide patient care and facilitate development of novel therapeutics.

METHODS

Serum creatinine, cystatin C, IL-6, and IL-8 and urine IL-18, NGAL, IL-6, and IL-8 were measured before and within 24 hours after liver transplantation in 40 patients. AKI was defined as a ≥50% sustained increase in creatinine above pre-operative values occurring within 24 hours of transplantation and persisting for at least 24 hours.

RESULTS

Seven patients met criteria for AKI (17.5%), with mean creatinines of 0.81 mg/dL pre-operatively and 1.75 mg/dL post-operatively. While pre-operative biomarker levels in patients with AKI were similar to those in patients without AKI, differences were seen between the groups with regard to median post-operative serum IL-8 (pg/mL) (242.48 vs. 82.37, p = 0.0463) and urine NGAL (ng/mL) (386.86 vs. 24.31, p = 0.0039), IL-6 (pg/mL) (52 vs. 7.29, p=0.0532), IL-8 (pg/mL) (14.3 vs. 0, p = 0.0224), and IL-18 (pg/mL) (883.09 vs. 0, p = 0.0449). The areas under receiver operating characteristic (ROC) curves were 0.749 for urine IL-18, 0.833 for urine NGAL, 0.745 for urine IL-6, 0.682 for serum IL-6, 0.773 for urine IL-8, and 0.742 for serum IL-8. Post-operative cystatin C was not significantly different between AKI and no AKI groups.

CONCLUSION

Serum IL-8 and urine IL-18, NGAL, IL-6, and IL-8 are elevated in AKI within the first 24 hours following liver transplantation.

Urinary neutrophil gelatinase-associated lipocalin may aid prediction of renal decline in patients with non-proteinuric Stages 3 and 4 chronic kidney disease (CKD)

BACKGROUND

Chronic kidney disease (CKD) is an increasing public health issue. It is therefore potentially highly advantageous to identify patients at risk of accelerated renal progression and death. Neutrophil gelatinase-associated lipocalin (NGAL) is an established urinary biomarker for acute kidney injury, but it is not known whether adding urinary NGAL (uNGAL) measurements to conventional risk factors will improve risk assessment in the setting of chronic disease.

METHODS

This is a prospective observational cohort study of 158 patients with Stage 3 or 4 CKD. The ability of baseline uNGAL to improve prediction of outcome was assessed by multivariate modelling and a number of metrics including net reclassification analysis. A primary composite endpoint of all-cause mortality or progression to end-stage renal disease (ESRD) requiring renal replacement therapy (RRT) at 2 years and a secondary endpoint of ≥5 mL/min/1.73 m(2) decline in the estimated glomerular filtration rate (eGFR) after 1 year were considered.

RESULTS

Forty patients (25%) reached the primary composite endpoint, 20 of whom died. Twenty-seven patients (19%) reached the secondary endpoint of a ≥5 mL/min/1.73 m(2) decline in the eGFR. The baseline uNGAL-to-creatinine ratio (uNCR) was associated with the combined endpoint of death or initiation of RRT (HR per 5 µg/mmol increase 1.27, 95% CI: 1.01-1.60, P = 0.036) independent of conventional cardiovascular and renal risk factors, including proteinuria. In separate analysis of these two competing endpoints, however, uNCR only remained associated with increased risk of progression to ESRD requiring RRT. Higher baseline uNCR was also independently predictive of rapid renal decline over 1 year (HR per 5 µg/mmol increase 1.47, 95% CI: 1.06-2.06, P = 0.022). Addition of uNCR to the base model resulted in a significant increase in discrimination for the secondary (C-statistic 0.76-0.85, P = 0.001) but not the primary endpoint (P = 0.276). Reclassification analysis on the other hand, demonstrated an improvement in risk predication of both primary and secondary endpoints by incorporating uNCR into the base model, but only in those with low-level urine protein excretion (<28 mg/mmol), with category-free net reclassification improvement (NRI) scores of 64% (95% CI: 8-70; P = 0.019) and 79% (95% CI: 12-83; P = 0.009), respectively.

CONCLUSION

The utilization of uNCR in addition to conventional established cardiovascular and renal risk factors may improve the prediction of disease progression in elderly Caucasian pre-dialysis CKD patients with low-grade proteinuria.

Urinary cystatin C and acute kidney injury after cardiac surgery

BACKGROUND

Acute kidney injury (AKI) is common after cardiac surgery and is associated with adverse patient outcomes. Urinary cystatin C (CysC) level is a biomarker of proximal tubule function and may increase earlier in AKI than serum creatinine level.

STUDY DESIGN

Prospective cohort study.

SETTINGS & PARTICIPANTS

The TRIBE AKI (Translational Research Investigating Biomarker Endpoints in AKI) Consortium prospectively enrolled 1,203 adults and 299 children and adolescents at 8 institutions in 2007-2009.

INDEX TEST

Urinary CysC (in milligrams per liter) within the first 12 hours after surgery.

OUTCOME

Serum creatinine-based AKI was defined as AKI Network stage 1 (mild AKI) and doubling of serum creatinine from the preoperative value or need for dialysis during hospitalization (severe AKI).

OTHER MEASUREMENTS

Analyses were adjusted for characteristics used clinically for AKI risk stratification, including age, sex, race, estimated glomerular filtration rate, diabetes, hypertension, heart failure, nonelective surgery, cardiac catheterization within 72 hours, type of surgery, myocardial infarction, and cardiopulmonary bypass time longer than 120 minutes.

RESULTS

Urinary CysC level measured in the early postoperative period (0-6 and 6-12 hours postoperatively) correlated with both mild and severe AKI in adults and children. However, after analyses were adjusted for other factors, the effect was attenuated for both forms of AKI in both cohorts.

LIMITATIONS

Limited numbers of patients with severe AKI and in-hospital dialysis treatment.

CONCLUSIONS

Urinary CysC values are not associated significantly with the development of AKI after cardiac surgery in adults and children.

Risk factors for and outcomes of acute kidney injury in neonates undergoing complex cardiac surgery

OBJECTIVE

To characterize the epidemiology of and identify risk factors for neonatal cardiac surgery-associated acute kidney injury (CS-AKI) and determine its impact on clinical outcomes.

STUDY DESIGN

Using secondary analysis of data from an ongoing multiprovincial prospective cohort study, we studied 264 neonates undergoing complex cardiac repair. CS-AKI was defined based on the Acute Kidney Injury Network (AKIN) definition. We used regression modeling and survival analysis (adjusting for covariates) to evaluate associations.

RESULTS

CS-AKI occurred in 64% of the neonates in our study cohort. Lower age, longer cardiopulmonary bypass time, hypothermic circulatory arrest, type of repair, lower preoperative serum creatinine (SCr) level, lower gestational age, and preoperative ventilation were independent risk factors for developing CS-AKI. Neonates with CS-AKI had longer times to extubation, intensive care discharge, and hospital discharge, after adjusting for covariates. Mortality was significantly increased in neonates with AKIN stage 2 or higher CS-AKI. The neonates with CS-AKI had a lower z-score for height at 2-year follow-up and were seen by more specialists.

CONCLUSION

Neonatal CS-AKI is common and independently predicts important clinical outcomes, including mortality. Many risk factors are similar to those in older children, but some are unique to neonates. The observation that lower baseline SCr predicts CS-AKI merits further study. The AKIN definition, based on preoperative SCr value, is a reasonable method for defining CS-AKI in neonates. Many previous studies of CS-AKI have excluded neonates; we suggest that future intervention studies on approaches to reducing CS-AKI incidence and improving outcomes should include neonates.

Fluid overload in infants following congenital heart surgery

OBJECTIVE

To describe postoperative fluid overload patterns and correlate degree of fluid overload with intensive care morbidity and mortality in infants undergoing congenital heart surgery.

DESIGN

Prospective, observational study. Fluid overload (%) was calculated by two methods: 1) (Total fluid in - Total fluid out)/(Preoperative weight) × 100; and 2) (Current weight - Preoperative weight)/(Preoperative weight) × 100. Composite poor outcome included: need for renal replacement therapy, upper quartile time to extubation or intensive care length of stay (> 6.5 and 9.9 days, respectively), or death ≤ 30 days after surgery.

SETTING

University hospital pediatric cardiac ICU.

PATIENTS

Forty-nine infants < 6 months of age undergoing congenital heart surgery with cardiopulmonary bypass during the period of July 2009 to July 2010.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients had a median age of 53 days (21 neonates) and mean weight of 4.5 ± 1.3 kg. Forty-two patients (86%) developed acute kidney injury by meeting at least Acute Kidney Injury Network and Kidney Disease Improving Global Outcomes stage 1 criteria (serum creatinine rise of 50% or ≥ 0.3mg/dL). The patients with adverse outcomes (n = 17, 35%) were younger (7 [5 - 10] vs. 98 [33 - 150] days, p = 0.001), had lower preoperative weight (3.7 ± 0.7 vs. 4.9 ± 1.4 kg, p = 0.0002), higher postoperative mean peak serum creatinine (SCr) (0.9 ± 0.3 vs. 0.6 ± 0.3mg/dL, p = 0.005), and higher mean maximum fluid overload by both method 1 (12% ± 10% vs. 6% ± 4%, p = 0.03) and method 2 (24% ± 15% vs. 14% ± 8%, p = 0.02). Predictors of a poor outcome from multivariate analyses were cardiopulmonary bypass time, use of circulatory arrest, and increased vasoactive medication requirements postoperatively.

CONCLUSIONS

Early postoperative fluid overload is associated with suboptimal outcomes in infants following cardiac surgery. Because the majority of patients developed kidney injury without needing renal replacement therapy, fluid overload may be an important risk factor for adverse outcomes with all degrees of acute kidney injury.

Perioperative acute kidney injury

The incidence of acute kidney injury (AKI) is generally 5-7.5% in all acute care hospitalizations and accounts for up to 20% of admissions to intensive care units (ICUs). Of all of the cases of AKI during hospitalization, approximately 30-40% are observed in operative settings. AKI is a serious morbidity that is associated with greater length of hospital stay, high risk of hospital mortality, and increased risk of incident and progressive chronic kidney disease. The incidence of AKI is variable depending on the specific surgical setting under consideration. Much of our knowledge regarding the epidemiology of AKI is derived from studies related to cardiac or vascular surgery. With limited treatment options, prevention of AKI and amelioration of its severity remain important cornerstones of improving patient outcomes. The magnitude of the problem and the unique set of patient characteristics calls for a multidisciplinary approach for the perioperative management of renal complications. The purpose of the review presented here is to discuss the current knowledge regarding the epidemiology and risk factors, outcomes, diagnoses, and prevention and treatment of AKI during the perioperative period in cardiovascular and noncardiovascular surgical settings.

Chronic kidney disease following acute kidney injury-risk and outcomes

In the past two decades, a substantial increase in the incidence of acute kidney injury (AKI) and kidney injury requiring dialysis has occurred in North America. This increase has coincided with an increase in the incidence of end-stage renal disease (ESRD), which has exceeded that expected based upon the prevalence of chronic kidney disease (CKD). In order to better understand the association between these conditions, there has been a proliferation of studies that have examined the risks of incident and progressive CKD following AKI. Animal studies have shown that failed differentiation of epithelial cells following renal ischaemia-reperfusion injury might lead to tubulointerstitial fibrosis, supporting a biological mechanism linking AKI and CKD. Strong and consistent associations between AKI and incident CKD, progression of CKD and incident ESRD have also been shown in epidemiological studies. In this Review, we summarize the wealth of available data on the relationship between AKI and CKD, and discuss the implications of these findings for the long-term clinical management of patients following AKI. We also identify areas of active investigation and future directions for research.

Advances in acute kidney injury associated with cardiac surgery: the unfolding revolution in early detection

Cardiac surgery-associated acute kidney injury (CSA-AKI) is important because it remains common and serious. A major limitation in the management of CSA-AKI has been ongoing delayed diagnosis by standard clinical approaches, including serum creatinine and calculated glomerular filtration rate. Recent advances in the understanding of CSA-AKI have highlighted the utility of novel biomarkers that diagnose CSA-AKI within the first 24 hours. The biomarkers that have been evaluated in clinical trials include neutrophil gelatinase-associated lipocalin (NGAL), cystatin C, kidney injury molecule 1 and interleukin-18. The biomarker with the greatest clinical promise is NGAL. Although it has multiple advantages over serum creatinine, it is still not the ideal biomarker for CSA-AKI. It is likely that a panel of early biomarkers will be developed to facilitate rapid and reliable detection of CSA-AKI, combining their different characteristics to optimize patient management. Future clinical trials likely will focus on whether these biomarkers predict adverse outcomes independent of serum creatinine fluctuations and whether therapies guided by biomarker profiles improve renal salvage and overall clinical outcomes. Given their clinical utility, these novel biomarkers have been evaluated beyond cardiac surgery for AKI in multiple clinical environments, including the emergency department, the operating room, the cardiac catheterization laboratory, and the intensive care unit. Their integration into clinical practice seems likely in the near future.

Urinary angiotensinogen and risk of severe AKI

BACKGROUND

Biomarkers of AKI that can predict which patients will develop severe renal disease at the time of diagnosis will facilitate timely intervention in populations at risk of adverse outcomes.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Liquid chromatography/tandem mass spectrometry was used to identify 30 potential prognostic urinary biomarkers of severe AKI in a group of patients that developed AKI after cardiac surgery. Angiotensinogen had the best discriminative characteristics. Urinary angiotensinogen was subsequently measured by ELISA and its prognostic predictive power was verified in 97 patients who underwent cardiac surgery between August 1, 2008 and October 6, 2011.

RESULTS

The urine angiotensinogen/creatinine ratio (uAnCR) predicted worsening of AKI, Acute Kidney Injury Network (AKIN) stage 3, need for renal replacement therapy, discharge >7 days from sample collection, and composite outcomes of AKIN stage 2 or 3, AKIN stage 3 or death, and renal replacement therapy or death. The prognostic predictive power of uAnCR was improved when only patients classified as AKIN stage 1 at the time of urine sample collection (n=79) were used in the analysis, among whom it predicted development of stage 3 AKI or death with an area under the curve of 0.81. Finally, category free net reclassification improvement showed that the addition of uAnCR to a clinical model to predict worsening of AKI improved the predictive power.

CONCLUSIONS

Elevated uAnCR is associated with adverse outcomes in patients with AKI. These data are the first to demonstrate the utility of angiotensinogen as a prognostic biomarker of AKI after cardiac surgery.

Whole blood assessment of neutrophil gelatinase-associated lipocalin versus pediatricRIFLE for acute kidney injury diagnosis and prognosis after pediatric cardiac surgery: cross-sectional study*

OBJECTIVE

To assess the ability of a single whole blood neutrophil gelatinase-associated lipocalin measurement in predicting acute kidney injury occurrence, its severity, and the need for postoperative renal replacement therapy after pediatric cardiac surgery.

DESIGN

Single-center prospective cross-sectional study.

SETTING

Tertiary care pediatric cardiac intensive care unit.

PATIENTS

Consecutive children <1 yr old with congenital heart diseases undergoing cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Neutrophil gelatinase-associated lipocalin levels were measured after pediatric cardiac intensive care unit admission. Pediatric score indicating level of renal damage by Risk, Injury, Failure, Loss of function and End-stage kidney disease (pRIFLE) was used as the reference method. Acute kidney injury was diagnosed in 90 (56%) of the 160 enrolled patients. The number of abnormal neutrophil gelatinase-associated lipocalin samples (above the cutoff level of 150 ng/mL) was 12 over 90 (13%) in acute kidney injury population and 6 over 70 in non-acute kidney injury patients (8%) (odds ratio 1.6; 95% confidence interval 0.6-4.7; p = .31). Sensitivity of neutrophil gelatinase-associated lipocalin for acute kidney injury detection was 0.13 and specificity 0.91. The number of patients with abnormal neutrophil gelatinase-associated lipocalin samples was not significantly different within pediatric score indicating level of renal damage by pRIFLE (p = .69); furthermore, we found abnormal neutrophil gelatinase-associated lipocalin levels in 4 (30%) over 13 renal replacement therapy patients and in 14 (10%) over 133 children without renal replacement therapy need (odds ratio 4.2; 95% confidence interval 1.2-10.2; p = .02). Mean cross-clamp time (p = .28), inotropic score (p = .19), surgical risk score (p = .3), mean length of mechanical ventilation (p = .48), and pediatric cardiac intensive care unit stay (p = .57) did not significantly differ between children with abnormal and normal neutrophil gelatinase-associated lipocalin values.

CONCLUSIONS

Neutrophil gelatinase-associated lipocalin measured at pediatric cardiac intensive care unit arrival does not accurately predict acute kidney injury diagnosis, according to pediatric score indicating level of renal damage by pRIFLE classification. In these patients, neutrophil gelatinase-associated lipocalin might be helpful for renal replacement therapy prediction.

New biomarkers for the quick detection of acute kidney injury

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Biomarkers of acute kidney injury in pediatric cardiac patients

Acute kidney injury is a common and significant complication among pediatric patients with congenital heart disease, occurring most commonly after cardiopulmonary bypass. Current laboratory methods of diagnosis are not timely enough to guide management decisions, thus spurring interest in discovering new biomarkers of acute injury. Several promising candidates, including NGAL, IL-18 and KIM-1, have been the subject of recent investigation and may facilitate earlier and more accurate diagnosis of renal injury within this cohort. There is little evidence demonstrating that it will be possible to rely upon one particular biomarker as a single agent, and evidence supports that the use of biomarker panels will be most effective. Further clinical validation and broader commercial availability of these novel biomarkers will probably revolutionize the care of pediatric cardiac patients with renal injury.

Are we ready for the clinical use of novel acute kidney injury biomarkers?

Acute kidney injury (AKI) is a common event in several neonatal populations, and those neonates with AKI have poor outcomes. Serum creatinine (SCr)-based definitions of AKI are not ideal and are additionally limited in neonates whose SCr reflects the maternal creatinine level at birth and normally drops over the first weeks of life dependent on gestational age. Recent studies show that urine and serum biomarkers may provide a better basis than SCr on which to diagnose AKI. In this month's issue of Pediatric Nephrology, Sarafidis et al. show that urine neutrophil gelatinase-associated lipocalin (uNGAL), serum NGAL (sNGAL), and urine cystatin c (uCysC) are highest in those neonates with asphyxia who have elevated SCr. Furthermore, those with asphyxia without a concomitant rise in SCr levels have elevated levels of biomarkers compared to controls, suggesting a dose response. Once the SCr level returns to normal, the levels of novel AKI biomarkers continue to be elevated. While these findings strengthen the argument for the clinical use of these AKI biomarkers, further work is needed before they can be implemented in clinical practice. Large-scale observational multi-center studies are needed to test these biomarkers against hard clinical endpoints. In addition, randomized intervention trials which use biomarkers to define AKI need to be performed.

Serum and urine acute kidney injury biomarkers in asphyxiated neonates

BACKGROUND

We evaluated serum (s) cystatin C (CysC) and neutrophil gelatinase-associated lipocalin (NGAL) and urine (u) CysC, NGAL and kidney injury molecule-1 (KIM-1) as markers of acute kidney injury (AKI) in asphyxiated neonates.

METHODS

AKI biomarkers were measured in 13 asphyxiated neonates born at ≥ 36 weeks gestational age (eight with AKI and five without AKI) and 22 controls. AKI was defined as serum creatinine ≥ 1.5 mg/dl for >24 h or rising values >0.3 mg/dl from day of life (DOL) 1. Biomarkers were measured on DOL 1, 3, and 10.

RESULTS

Asphyxiated neonates had significantly higher sCysC on DOL 1 as well as sNGAL and uCysC and uNGAL (standardized to urine creatinine and absolute values) than controls at all time points. Compared to controls, significantly higher sNGAL, uCysC, and uNGAL values were observed in the asphyxia-AKI and asphyxia-no AKI subgroups. Regarding uKIM-1, only the absolute values were significantly higher in asphyxiated neonates (DOL 10). sNGAL, uCyst, and uNGAL had a significant diagnostic performance as predictors AKI on DOL 1.

CONCLUSIONS

sNGAL, uCysC, and uNGAL are sensitive, early AKI biomarkers, increasing significantly in asphyxiated neonates even in those not fulfilling AKI criteria. Their measurement on DOL 1 is predictive of post-asphyxia-AKI.

Mechanism-based urinary biomarkers to identify the potential for aminoglycoside-induced nephrotoxicity in premature neonates: a proof-of-concept study

Premature infants are frequently exposed to aminoglycoside antibiotics. Novel urinary biomarkers may provide a non-invasive means for the early identification of aminoglycoside-related proximal tubule renal toxicity, to enable adjustment of treatment and identification of infants at risk of long-term renal impairment. In this proof-of-concept study, urine samples were collected from 41 premature neonates (≤32 weeks gestation) at least once per week, and daily during courses of gentamicin, and for 3 days afterwards. Significant increases were observed in the three urinary biomarkers measured (Kidney Injury Molecule-1 (KIM-1), Neutrophil Gelatinase-associated Lipocalin (NGAL), and N-acetyl-β-D-glucosaminidase (NAG)) during treatment with multiple courses of gentamicin. When adjusted for potential confounders, the treatment effect of gentamicin remained significant only for KIM-1 (mean difference from not treated, 1.35 ng/mg urinary creatinine; 95% CI 0.05–2.65). Our study shows that (a) it is possible to collect serial urine samples from premature neonates, and that (b) proximal tubule specific urinary biomarkers can act as indicators of aminoglycoside-associated nephrotoxicity in this age group. Further studies to investigate the clinical utility of novel urinary biomarkers in comparison to serum creatinine need to be undertaken.