Urinary cystatin C and acute kidney injury after cardiac surgery

Advances in the diagnosis of early biomarkers for acute kidney injury: a literature review

Acute kidney injury (AKI) is a critical condition with diverse manifestations and variable outcomes. Its diagnosis traditionally relies on delayed indicators such as serum creatinine and urine output, making early detection challenging. Early identification is essential to improving patient outcomes, driving the need for novel biomarkers. Recent advancements have identified promising biomarkers across various biological processes. Tubular injury markers, including neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), N-acetyl-β-D-glucosaminidase (NAG), and liver-type fatty acid-binding protein (L-FABP), offer insights into early tubular damage. Inflammatory and repair-associated biomarkers, such as interleukin-18 (IL-18), monocyte chemotactic protein-1 (MCP-1), osteopontin (OPN), and C-C motif chemokine ligand 14 (CCL14), reflect ongoing injury and recovery processes. Additionally, stress and repair markers like tissue inhibitor of metalloproteinase-2 (TIMP-2) and insulin-like growth factor-binding protein-7 (IGFBP-7), alongside filtration markers such as cystatin C (CysC) and proenkephalin (PenKid®) e.tal, further enhance diagnostic precision. Oxidative stress-related markers, including Superoxide Dismutase 1 (SOD1), also contribute valuable information. Emerging candidates, such as microRNAs, soluble urokinase plasminogen activator receptor (SuPAR), and chitinase-3-like protein 1 (CHI3L1), hold substantial promise for AKI detection and prognosis. This review summarizes the progress in AKI biomarker research, highlighting their clinical utility and exploring their potential to refine early diagnosis and management strategies. These findings offer a new perspective for integrating novel biomarkers into routine clinical practice, ultimately improving AKI care.

Cystatin C and Kidney Function Recovery in Patients Requiring Continuous KRT for Acute Kidney Injury

Key Points

Plasma cystatin C is decreased in participants with AKI requiring continuous KRT (CKRT) with early kidney function recovery. Despite being cleared by CKRT, plasma cystatin C in the first 3 days of CKRT may be a useful clinical tool to help predict the prognosis of AKI requiring CKRT.

Background

Plasma cystatin C is a reliable marker to estimate kidney function; however, it is unknown whether this remains true in patients receiving continuous KRT (CKRT). In this study, we tested the hypothesis that lower concentrations of plasma cystatin C during the first 3 days of CKRT would predict kidney function recovery.

Methods

We performed a retrospective observational study of 72 patients from a 126-patient, single-center CKRT study. We studied two a priori defined cohorts of patients without advanced CKD who had AKI requiring CKRT: (1 ) with early kidney function recovery defined as liberation from KRT within 7 days of CKRT initiation versus (2 ) with delayed kidney function recovery defined as receipt of KRT for >21 days or death while on KRT. Subsequent analysis included patients with advanced CKD and intermediate kidney function recovery (liberation between 8 and 21 days). Cystatin C was then measured on stored plasma, urine, and dialysis effluent collected before CKRT initiation and on days 1, 2, and 3 of CKRT.

Results

Plasma cystatin C was significantly lower in patients with early kidney function recovery in comparison with patients with delayed kidney function recovery on days 1 (1.79 versus 2.39 mg/L), 2 (1.91 versus 2.38 mg/L), and 3 (2.04 versus 2.67 mg/L) of CKRT. Sieving coefficient and CKRT clearance of cystatin C were similar for patients with early and delayed kidney function recovery. The lowest plasma cystatin C concentration on days 1–3 of CKRT predicted early kidney function recovery with an area under the receiver operating curve of 0.77 (P =0.002), positive likelihood ratio of 5.60 for plasma cystatin C <1.30 mg/L, and negative likelihood ratio of 0.17 for plasma cystatin C ≥1.88 mg/L.

Conclusions

Lower plasma cystatin C concentrations during the first 3 days of CKRT are associated with early kidney function recovery.

Future embracing: exosomes driving a revolutionary approach to the diagnosis and treatment of idiopathic membranous nephropathy

Membranous nephropathy (MN) is a leading cause of nephrotic syndrome in adults and is associated with high rates of end-stage renal disease. Early detection and precise interventions are crucial for improving patient prognosis and quality of life. However, the current diagnosis primarily relies on renal biopsies and traditional biomarkers, which have limitations. Additionally, targeted therapeutic strategies are lacking. Exosomes, small vesicles that facilitate intercellular communication, have emerged as potential noninvasive diagnostic markers due to their stability, diverse cargo, and rapid detectability. They also hold promise as carriers for gene and drug delivery, presenting innovative opportunities in renal disease prognosis and treatment. However, research on exosomes in the context of idiopathic membranous nephropathy (IMN) remains limited, with a focus on exploring urinary exosomes as IMN markers. In this review, we summarize the current status of MN diagnosis and treatment, highlight the fundamental characteristics of exosomes, and discuss recent advancements in their application to IMN diagnosis and therapy. We provide insights into the clinical prospects of exosomes in IMN and acknowledge potential challenges. This article aims to offer forward-looking insights into the future of exosome-mediated IMN diagnosis and treatment, indicating a revolutionary transformation in this field.

Acute Kidney Injury Requiring Dialysis After Pediatric Heart Transplant

BACKGROUND

Acute kidney injury (AKI) is a common complication of pediatric heart transplant, with a subset of patients developing severe AKI requiring dialysis (AKI-D). We aimed to identify the epidemiology, risk factors, and outcomes of postoperative AKI-D in pediatric heart transplant recipients.

METHODS

We retrospectively identified all pediatric first-time, single-organ heart transplants at our institution from 2014 to 2022. Postoperative AKI was defined as AKI within 2 weeks of transplant. Unadjusted and adjusted logistic regression were used to identify characteristics associated with AKI-D, and unadjusted time-to-event analyses were used to determine the association between AKI-D and survival free of kidney failure.

RESULTS

Among 177 patients included, 116 (66%) developed postoperative AKI of any stage, including 13 (7%) who developed AKI-D with median time from transplant to dialysis initiation of 6 days (IQR 3-13). In adjusted models, increased cardiopulmonary bypass time (OR 1.19, 95% CI 1.04-1.37, per 15 min increase in bypass time) and higher weight at transplant were associated with higher odds of AKI-D, whereas patient demographics and pretransplant kidney function were not associated with AKI-D. AKI-D was associated with greater mortality during initial hospitalization (46% vs. 1%, p < 0.001) and a lower rate of survival free of kidney failure.

CONCLUSIONS

The incidence of AKI-D after pediatric heart transplant was 7%, with extended cardiopulmonary bypass time associated with postoperative AKI-D even in adjusted models. Further research is needed to improve the prediction and management of AKI-D in this population.

Association of Urine Biomarkers With Acute Kidney Injury and Fluid Overload in Infants After Cardiac Surgery: A Single Center Ancillary Cohort of the Steroids to Reduce Systemic Inflammation After Infant Heart Surgery Trial

To examine the association between three perioperative urine biomarker concentrations (urine cystatin C [uCysC], urine neutrophil gelatinase-associated lipocalin [uNGAL], and urine kidney injury molecule 1 [uKIM-1]), and cardiac surgery-associated acute kidney injury (CS-AKI) and fluid overload (FO) in infants with congenital heart disease undergoing surgery on cardiopulmonary bypass. To explore how urine biomarkers are associated with distinct CS-AKI phenotypes based on FO status.

DESIGN

Ancillary prospective cohort study.

SETTING

Single U.S. pediatric cardiac ICU.

PATIENTS

Infants less than 1 year old enrolled in the Steroids to Reduce Systemic Inflammation after Infant Heart Surgery trial (NCT03229538) who underwent heart surgery from June 2019 to May 2020 and opted into biomarker collection at a single center. Infants with preoperative CS-AKI were excluded.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Forty infants met inclusion criteria. Median (interquartile) age at surgery was 103 days (5.5-161 d). Modified Kidney Disease Improving Global Outcomes-defined CS-AKI was diagnosed in 22 (55%) infants and 21 (53%) developed FO. UCysC and uNGAL peaked in the early postoperative period and uKIM-1 peaked later. In unadjusted analysis, bypass time was longer, and Vasoactive-Inotropic Score at 24 hours was higher in infants with CS-AKI. On multivariable analysis, higher uCysC (odds ratio [OR], 1.023; 95% CI, 1.004-1.042) and uNGAL (OR, 1.019; 95% CI, 1.004-1.035) at 0-8 hours post-bypass were associated with FO. UCysC, uNGAL, and uKIM-1 did not significantly correlate with CS-AKI. In exploratory analyses of CS-AKI phenotypes, uCysC and uNGAL were highest in CS-AKI+/FO+ infants.

CONCLUSIONS

In this study, uCysC and uNGAL in the early postoperative period were associated with FO at 48 hours. UCysC, uNGAL, and uKIM-1 were not associated with CS-AKI. Further studies should focus on defining expected concentrations of these biomarkers, exploring CS-AKI phenotypes and outcomes, and establishing clinically meaningful endpoints for infants post-cardiac surgery.

Improving acute kidney injury diagnostic precision using biomarkers

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

Biomarkers of acute kidney injury after pediatric cardiac surgery: a meta-analysis of diagnostic test accuracy

Acute kidney injury (AKI) occurs frequently after cardiac surgery in children. Although current diagnostic criteria rely on serum creatinine and urine output, changes occur only after considerable loss of kidney function. This meta-analysis aimed to synthesize the knowledge on novel biomarkers and compare their ability to predict AKI. PubMed/MEDLINE, Embase, Scopus, and reference lists were searched for relevant studies published by March 2021. Diagnostic accuracy parameters were extracted and analyzed using hierarchical summary receiver operating characteristic (HSROC) method. Pooled estimates of the area under the curve (AUC) were calculated using conventional random-effects meta-analysis. Fifty-six articles investigating 49 biomarkers in 8617 participants fulfilled our eligibility criteria. Data from 37 studies were available for meta-analysis. Of the 10 biomarkers suitable for HSROC analysis, urinary neutrophil gelatinase-associated lipocalin (uNGAL) to creatinine (Cr) ratio yielded the highest diagnostic odds ratio (91.0, 95% CI 90.1-91.9), with a sensitivity of 91.3% (95% CI 91.2-91.3%) and a specificity of 89.7% (95% CI 89.6-89.7%). These results were confirmed in pooled AUC analysis, as uNGAL-to-Cr ratio and uNGAL were the only elaborately studied biomarkers (> 5 observations) with pooled AUCs ≥ 0.800. Liver fatty acid-binding protein (L-FABP), serum cystatin C (sCysC), serum NGAL (sNGAL), and interleukin-18 (IL-18) all had AUCs ≥ 0.700.

CONCLUSION

A variety of biomarkers have been proposed as predictors of cardiac surgery-associated AKI in children, of which uNGAL was the most prominent with excellent diagnostic qualities. However, more consolidatory evidence will be required before these novel biomarkers may eventually help realize precision medicine in AKI management.

WHAT IS KNOWN

• Acute kidney injury (AKI) occurs in about 30-60% of children undergoing cardiac surgery and is associated with increased in-hospital mortality and adverse short-term outcomes. However, in current clinical practice, AKI definitions and detection often rely on changes in serum creatinine and urine output, which are late and insensitive markers of kidney injury. • Although various novel biomarkers have been studied for the diagnosis of AKI in children after cardiac surgery, it remains unclear how these compare to one another in terms of diagnostic accuracy.

WHAT IS NEW

• Pooled analyses suggest that for the diagnosis of AKI in children who underwent cardiac surgery, NGAL is the most accurate among the most frequently studied biomarkers. • A number of other promising biomarkers have been reported, although they will require further research into their diagnostic accuracy and clinical applicability.

Biomarkers of acute kidney injury in pediatric cardiac surgery

Acute kidney injury (AKI) is characterized by a sudden decrease in kidney function. Children with congenital heart disease are a special group at risk of developing AKI. We performed a systematic review of the literature to search for studies reporting the usefulness of novel urine, serum, and plasma biomarkers in the diagnosis and progression of AKI and their association with clinical outcomes in children undergoing pediatric cardiac surgery. In thirty studies, we analyzed the capacity to predict AKI and poor outcomes of five biomarkers: Cystatin C, Neutrophil gelatinase-associated lipocalin, Interleukin-18, Kidney injury molecule-1, and Liver fatty acid-binding protein. In conclusion, we suggest the need for further meta-analyses with the availability of additional studies.

The use of diagnostic tools for pediatric AKI: applying the current evidence to the bedside

Given the known deleterious consequences of acute kidney injury (AKI), exciting recent research efforts have focused on developing strategies for the earlier recognition of AKI in the pediatric population. Recognizing the limitations of serum creatinine, investigators have focused on the study of novel biomarkers and practical bedside tools for identifying patients at risk for AKI prior to a rise in serum creatinine. In PubMed, there are presently over 30 original research papers exploring the use of pediatric AKI risk prediction tools in just the last 2 years. The following review highlights the most recent advances in the literature regarding opportunities to refine our ability to detect AKI early. Importantly, this review discusses how prediction tools including novel urine and serum biomarkers, practical risk stratification tests, renal functional reserve, and electronic medical record alerts may ultimately be applied to routine clinical practice.

Biomarkers in Acute Kidney Injury

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

Acute kidney injury in the critically ill: an updated review on pathophysiology and management

Acute kidney injury (AKI) is now recognized as a heterogeneous syndrome that not only affects acute morbidity and mortality, but also a patient’s long-term prognosis. In this narrative review, an update on various aspects of AKI in critically ill patients will be provided. Focus will be on prediction and early detection of AKI (e.g., the role of biomarkers to identify high-risk patients and the use of machine learning to predict AKI), aspects of pathophysiology and progress in the recognition of different phenotypes of AKI, as well as an update on nephrotoxicity and organ cross-talk. In addition, prevention of AKI (focusing on fluid management, kidney perfusion pressure, and the choice of vasopressor) and supportive treatment of AKI is discussed. Finally, post-AKI risk of long-term sequelae including incident or progression of chronic kidney disease, cardiovascular events and mortality, will be addressed.

Urinary EGF and MCP-1 and risk of CKD after cardiac surgery

BACKGROUNDAssessment of chronic kidney disease (CKD) risk after acute kidney injury (AKI) is based on limited markers primarily reflecting glomerular function. We evaluated markers of cell integrity (EGF) and inflammation (monocyte chemoattractant protein-1, MCP-1) for predicting long-term kidney outcomes after cardiac surgery.METHODSWe measured EGF and MCP-1 in postoperative urine samples from 865 adults who underwent cardiac surgery at 2 sites in Canada and the United States and assessed EGF and MCP-1's associations with the composite outcome of CKD incidence or progression. We used single-cell RNA-Seq (scRNA-Seq) of AKI patient biopsies to perform transcriptomic analysis of programs corregulated with the associated genes.RESULTSOver a median (IQR) follow-up of 5.8 (4.2-7.1) years, 266 (30.8%) patients developed the composite CKD outcome. Postoperatively, higher levels of urinary EGF were protective and higher levels of MCP-1 were associated with the composite CKD outcome (adjusted HR 0.83, 95% CI 0.73-0.95 and 1.10, 95% CI 1.00-1.21, respectively). Intrarenal scRNA-Seq transcriptomes in patients with AKI-defined cell populations revealed concordant changes in EGF and MCP-1 levels and underlying molecular processes associated with loss of EGF expression and gain of CCL2 (encoding MCP-1) expression.CONCLUSIONUrinary EGF and MCP-1 were each independently associated with CKD after cardiac surgery. These markers may serve as noninvasive indicators of tubular damage, supported by tissue transcriptomes, and provide an opportunity for novel interventions in cardiac surgery.TRIAL REGISTRATIONClinicalTrials.gov NCT00774137.FUNDINGThe NIH funded the TRIBE-AKI Consortium and Kidney Precision Medicine Project. Yale O'Brien Kidney Center, American Heart Association, Patterson Trust Fund, Dr. Adam Linton Chair in Kidney Health Analytics, Canadian Institutes of Health Research, ICES, Ontario Ministry of Health and Long-Term Care, Academic Medical Organization of Southwestern Ontario, Schulich School of Medicine & Dentistry, Western University, Lawson Health Research Institute, Chan Zuckerberg Initiative Human Cell Atlas Kidney Seed Network.

Results from the TRIBE-AKI Study found associations between post-operative blood biomarkers and risk of chronic kidney disease after cardiac surgery

Patients undergoing cardiac surgery are placed under intense physiologic stress. Blood and urine biomarkers measured peri-operatively may help identify patients at higher risk for adverse long-term kidney outcomes.We sought to determine independent associations of various biomarkers with development or progression of chronic kidney disease (CKD) following cardiac surgery. In this sub-study of the prospective cohort -TRIBE-AKI Study, we evaluated 613 adult patients undergoing cardiac surgery in Canada in our primary analysis and tested the association of 40 blood and urinary biomarkers with the primary composite outcome of CKD incidence or progression. In those with baseline estimated glomerular filtration rate (eGFR) over 60 mL/min/1.73m2, we defined CKD incidence as a 25% reduction in eGFR and an eGFR under 60. In those with baseline eGFR under 60 mL/min/1.73m2, we defined CKD progression as a 50% reduction in eGFR or eGFR under 15. Results were evaluated in a replication cohort of 310 patients from one study site in the United States. Over a median follow-up of 5.6 years, 172 patients developed the primary outcome. Each log increase in basic fibroblast growth factor (adjusted hazard ratio 1.52 [95% confidence interval 1.19, 1.93]), Kidney Injury Molecule-1 (1.51 [0.98, 2.32]), N-terminal pro-B-type natriuretic peptide (1.19 [1.01, 1.41]), and tumor necrosis factor receptor 1 (1.75 [1.18, 2.59]) were associated with outcome after adjustment for demographic factors, serum creatinine, and albuminuria. Similar results were noted in the replication cohort. Although there was no interaction by acute kidney injury in continuous analysis, mortality was higher in the no acute kidney injury group by biomarker tertile. Thus, elevated post-operative levels of blood biomarkers following cardiac surgery were independently associated with the development of CKD. These biomarkers can provide additional value in evaluating CKD incidence and progression after cardiac surgery.

Development of acute kidney injury following pediatric cardiac surgery

Acute kidney injury (AKI) in the pediatric population is a relatively common phenomenon. Specifically, AKI has been found in increasing numbers within the pediatric population following cardiac surgery, with up to 43% of pediatric patients developing AKI post-cardiac surgery. However, recent advances have allowed for the identification of risk factors. These can be divided into preoperative, intraoperative, and postoperative factors. Although the majority of pediatric patients developing AKI after cardiac surgery completely recover, this condition is associated with worse outcomes. These include fluid overload and increased mortality and result in longer hospital and intensive care unit stays. Detecting the presence of AKI has advanced; use of relatively novel biomarkers, including neutrophil gelatinase associated lipocalin, has shown promise in detecting more subtle changes in kidney function when compared to conventional methods. While a single, superior treatment has not been elucidated yet, novel functions of medications, including fenoldopam, theophylline and aminophylline, have been shown to have better outcomes for these patients. With the recent advances in identification of risk factors, outcomes, diagnosis, and management, the medical community can further explain the complexities of AKI in the pediatric population post-cardiac surgery.

Developing Biomarker Panels to Predict Progression of Acute Kidney Injury After Cardiac Surgery

Introduction

Acute kidney injury (AKI) is a frequent complication of cardiac surgery, but only a fraction of cardiac surgery patients that experience postoperative AKI have progression to more severe stages. Biomarkers that can distinguish patients that will experience progression of AKI are potentially useful for clinical care and/or the development of therapies.

Methods

Data come from a prospective cohort study of cardiac surgery patients; the analytic dataset contained data from 354 cardiac surgery patients meeting criteria for AKI following surgery. Candidate predictors were 38 biomarkers of kidney function, insult, or injury measured at the time of AKI diagnosis. The outcome was AKI progression, defined as worsening of AKI Network stage. We investigated combining biomarkers with Bayesian model averaging (BMA) and random forests of classification trees, with and without center transformation. For both approaches, we used resampling-based methods to avoid optimistic bias in our assessment of model performance.

Results

BMA yielded a combination of 3 biomarkers and an optimism-corrected estimated area under the receiver operating characteristic curve (AUC) of 0.75 (95% confidence interval [CI]: 0.68, 0.82). The random forests approach, which nominally uses all biomarkers, had an estimated AUC of 0.74 (95% CI: 0.66, 0.82). A second application of random forests applied to biomarker values after a center-specific transformation had an estimated AUC of 0.80 (95% CI: 0.72, 0.88).

Conclusion

These findings suggest that the application of advanced statistical techniques to combine biomarkers offers only modest improvements over use of single biomarkers alone. This exemplifies a common experience in biomarker research: combinations of modestly performing biomarkers often also have modest performance.

Relative value of cystatin C and creatinine-based estimates of glomerular filtration rate in predicting long-term mortality after cardiac surgery: a cohort study

OBJECTIVE

Renal dysfunction predicts an increased risk of both early and long-term mortality after cardiac surgery. Cystatin C enables glomerular filtration rate (GFR) to be estimated accurately and may be superior in this regard to creatinine-based estimates. We hypothesised, therefore, that cystatin C and derived estimates of GFR would independently predict long-term survival after cardiac surgery and would be superior in this respect to traditional estimates of GFR. The current study tests this hypothesis in a large and well-characterised cohort of patients.

DESIGN

A prospective cohort study.

SETTING

Regional cardiothoracic centre in Northeast Scotland.

PARTICIPANTS

1010 patients undergoing non-emergent cardiac surgery between 2004 and 2007. Serum creatinine and cystatin C levels were measured preoperatively and demographic and clinical variables were recorded.

PRIMARY OUTCOME MEASURE

All-cause mortality, established from the National Records of Scotland.

RESULTS

The median duration of follow-up after surgery was 9.7 years (IQR 8.9-10.6 years), during which 297 participants died. Preoperative creatinine and cystatin C levels and estimates of GFR derived from these were all strong predictors of death using Cox regression and remained independently predictive after adjustment for the logistic European System for Cardiac Operative Risk Evaluation, a well-validated clinical risk score and a range of other clinical predictors. Cystatin C-based measures were superior to creatinine-based estimates of GFR.

CONCLUSIONS

Cystatin C and creatinine derived eGFR are powerful and independent predictors of long-term mortality following cardiac surgery. Estimates of GFR derived from cystatin C convey superior prognostic information to conventional creatinine-based estimates, but the observed differences are modest.

Are Urinary Biomarkers Better Than Acute Kidney Injury Duration for Predicting Readmission?

BACKGROUND

Acute kidney injury (AKI) is a common complication of cardiac surgery. Postprocedural AKI is a risk factor for 30-day readmission. We sought to examine the association of AKI and kidney injury biomarkers with readmission after cardiac surgery.

METHODS

Patients alive at discharge who underwent cardiac surgery from the Translational Research Investigating Biomarker Endpoints-AKI cohort were enrolled from six medical centers in the United States and Canada. AKI duration was defined as the total number of days AKI was present during index admission (no AKI, 1-2, 3-6, and 7+ days). Preoperative and postoperative urinary levels were collected for interleukin-18, neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, liver-fatty-acid-binding protein, cystatin C, microalbumin, creatinine, and albumin-to-creatinine ratio. Readmission and death events were identified through US (Medicare) and Canadian administrative databases at 30 days and 365 days after discharge.

RESULTS

Of 968 patients 15.9% were readmitted or died within 30 days of discharge and 35.9% were readmitted or died within 365 days. AKI duration of 3 to 6 days was significantly associated with 30-day readmission or death (adjusted odds ratio, 1.82%; 95% confidence interval, 1.08-3.05). Patients with AKI duration ≥ 7 days had increased odds of readmission or death at both 30 days (adjusted odds ratio, 2.49%; 95% confidence interval, 1.15-5.43) and 365 days (adjusted odds ratio, 3.67%; 95% confidence interval, 1.73-7.79). Urinary biomarkers had no association with readmission and death.

CONCLUSIONS

AKI duration ≥ 3 days, and not kidney biomarkers, was strongly associated with readmission or death. These clinical outcomes are potentially due to cardiovascular or hemodynamic causes rather than intrinsic injury to the kidney parenchyma.

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.

Urine KIM-1 as a Potential Biomarker of Acute Renal Injury After Circulatory Collapse in Children

OBJECTIVES

Serum creatinine (SCr) is a late marker of acute kidney injury (AKI) due to the lag time between initiating injury and loss of function. We assessed the ability of urinary interleukin-18 (IL-18), kidney injury molecule-1 (KIM-1), and neutrophil gelatinase-associated lipocalin (NGAL) to predict AKI in critically ill children with circulatory collapse.

METHODS

Serum creatinine, estimated creatinine clearance (eCrCL), urine IL-18, KIM-1, and NGAL values were measured in 86 children with circulatory collapse on the day of admission, and the results were compared with those obtained 6 days later. Acute kidney injury was defined as a decrease in eCrCL of greater than 25% within the first 48 hours of enrollment. Areas under the curve (AUC) for receiver operating characteristic curve were calculated for the early detection of AKI.

RESULTS

Mean SCr concentration did not differ significantly during the first 6 days of hospital admission. In contrast, mean urine concentrations of IL-18, KIM-1, and NGAL rose significantly from day of admission to the sixth day of hospital stay (P < 0.001). Urinary KIM-1 emerged as having the strongest performance for the early detection of AKI, followed by NGAL, IL-18, and eCrCL. Urinary KIM-1 displayed the highest AUC of 0.81 (95% confidence interval [CI], 0.76-0.93; P < 0.001) for the early detection of AKI after circulatory collapse, followed by NGAL (0.77% CI, 0.70-0.84) and IL-18 (0.69% CI, 0.48-0.64).

CONCLUSIONS

Of a panel of 3 promising urinary biomarkers, KIM-1 demonstrated the best performance in predicting AKI in children with circulatory collapse before a change in SCr or eCrCL becomes apparent.

Acute kidney injury after pediatric cardiac surgery

Acute kidney injury (AKI) is a common complication of pediatric cardiac surgery and is associated with increased morbidity and mortality. Literature of AKI after pediatric cardiac surgery is comprehensively reviewed in terms of incidence, risk factors, biomarkers, treatment and prognosis. The novel RIFLE (pediatric RIFLE for pediatrics), Acute Kidney Injury Network (AKIN) and Kidney Disease Improving Global Outcomes (KDIGO) criteria have brought about unified diagnostic standards and comparable results for AKI after cardiac surgery. Numerous risk factors, either renal or extrarenal, can be responsible for the development of AKI after cardiac surgery, with low cardiac output syndrome being the most pronounced predictor. Early fluid overload is also crucial for the occurrence of AKI and prognosis in pediatric patients. Three sensitive biomarkers, neutrophil gelatinase-associated lipocalin, cystatin C (CysC) and liver fatty acid-binding protein, are regarded as the earliest (increase at 2-4 h), and another two, kidney injury molecule-1 and interleukin-18 represent the intermediate respondents (increase at 6-12 h after surgery). To ameliorate the cardiopulmonary bypass techniques, improve renal perfusion and eradicate the causative risk factors are imperative for the prevention of AKI in pediatric patients. The early and intermediate biomarkers are helpful for an early judgment of occurrence of postoperative AKI. Improved survival has been achieved by prevention, renal support and modifications of hemofiltration techniques. Further development is anticipated in small children.

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

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

Prediction of contrast induced acute kidney injury using novel biomarkers following contrast coronary angiography

BACKGROUND/INTRODUCTION

Chronic kidney disease (CKD) is a risk factor for contrast induced acute kidney injury (CI-AKI). Contrast angiography in CKD patients is a common procedure. Creatinine is a delayed marker of CI-AKI and delays diagnosis which results in significant morbidity and mortality.

AIM

Early diagnosis of CI-AKI requires validated novel biomarkers.

DESIGN

A prospective observation study of 301 consecutive CKD patients undergoing coronary angiography was performed.

METHODS

Samples for plasma neutrophil gelatinase-associated lipocalin (NGAL), serum liver fatty acid-binding protein (L-FABP), serum kidney injury marker 1, serum interleukin 18 and serum creatinine were taken at 0, 1, 2, 4, 6 and 48 h post-contrast. Urinary NGAL and urinary cystatin C were collected at 0, 6 and 48 h. Incidence of major adverse clinical events (MACE) was recorded at 1 year. CI-AKI was defined as an absolute delta rise in creatinine of ≥26.5 µmol/l or a 50% relative rise from baseline at 48 h following contrast.

RESULTS

CI-AKI occurred in 28 (9.3%) patients. Plasma NGAL was most predictive of CI-AKI at 6 h. L-FABP performed best at 4 h. A combination of Mehran score > 10, 4 h L-FABP and 6 h NGAL improved specificity to 96.7%. MACE was statistically higher at 1 year in CI-AKI patients (25.0 vs. 6.2% in non-CI-AKI patients).

DISCUSSION/CONCLUSION

Mehran risk score, 4 h serum L-FAPB and 6 h plasma NGAL performed best at early CI-AKI prediction. CI-AKI patients were four times more likely to develop MACE and had a trebling of mortality risk at 1 year.

Development of biomarker combinations for postoperative acute kidney injury via Bayesian model selection in a multicenter cohort study

Background

Acute kidney injury (AKI) is a frequent complication of cardiac surgery. We sought prognostic combinations of postoperative biomarkers measured within 6 h of surgery, potentially in combination with cardiopulmonary bypass time (to account for the degree of insult to the kidney). We used data from a large cohort of patients and adapted methods for developing biomarker combinations to account for the multicenter design of the study.

Methods

The primary endpoint was sustained mild AKI, defined as an increase of 50% or more in serum creatinine over preoperative levels lasting at least 2 days during the hospital stay. Severe AKI (secondary endpoint) was defined as a serum creatinine increase of 100% or more or dialysis during hospitalization. Data were from a cohort of 1219 adults undergoing cardiac surgery at 6 medical centers; among these, 117 developed sustained mild AKI and 60 developed severe AKI. We considered cardiopulmonary bypass time and 22 biomarkers as candidate predictors. We adapted Bayesian model averaging methods to develop center-adjusted combinations for sustained mild AKI by (1) maximizing the posterior model probability and (2) retaining predictors with posterior variable probabilities above 0.5. We used resampling-based methods to avoid optimistic bias in evaluating the biomarker combinations.

Results

The maximum posterior model probability combination included plasma N-terminal-pro-B-type natriuretic peptide, plasma heart-type fatty acid binding protein, and change in serum creatinine from before to 0-6 h after surgery; the median probability combination additionally included plasma interleukin-6. The center-adjusted, optimism-corrected AUCs for these combinations were 0.80 (95% CI: 0.78, 0.87) and 0.81 (0.78, 0.87), respectively, for predicting sustained mild AKI, and 0.81 (0.76, 0.90) and 0.83 (0.76, 0.90), respectively, for predicting severe AKI. For these data, the Bayesian model averaging methods yielded combinations with prognostic capacity comparable to that achieved by standard frequentist methods but with more parsimonious models.

Conclusions

Pending external validation, the identified combinations could be used to identify individuals at high risk of AKI immediately after cardiac surgery and could facilitate clinical trials of renoprotective agents.

C-terminal fragment of agrin (CAF) levels predict acute kidney injury after acute myocardial infarction

Background

Patients with acute myocardial infarction are at high risk for acute kidney injury. Novel biomarkers that can predict acute kidney injury in AMI may allow timely interventions. C-terminal fragment of agrin (CAF), a proteoglycan of the glomerular and tubular basement membrane, have been recently associated with rapid renal function deterioration and proximal tubular dysfunction. It is unknown whether elevated CAF levels may serve as a novel AKI biomarker in patients presenting with AMI.

Methods

In 436 persons enrolled in a multicenter prospective observational cohort study of patients with acute myocardial infarction, we measured plasma and urine levels of several kidney injury biomarkers including CAF, neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18 (IL-18) and cystatin-C.The relationship between biomarker levels at baseline and the development of AKI and long-term mortality were analyzed after adjustment for demographic and clinical variables.

Results

AKI incidence was up to 15% during hospitalization. The predictive accuracy for AKI of urinary CAF was similar to NGAL and superior to other tested kidney injury biomarkers. In a multivariate model that included all possible confounding variables only urinary CAF continued to be an independent marker for AKI (OR 1.35 95%CI 1.05 -1.74). During the 2 years follow-up, only plasma CAF levels remained a significant independent predictor of mortality (OR 2.5 95%CI 1.02-6.2; P = 0.04).

Conclusions

Elevated CAF levels are associated with AKI in patients with acute myocardial infarction. Our study provides preliminary evidence that CAF levels may predict AKI and mortality after AMI in low risk patients with relative preserved kidney function at baseline.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-017-0611-9) contains supplementary material, which is available to authorized users.

Accuracy of cystatin C in prediction of acute kidney injury in children; serum or urine levels: which one works better? A systematic review and meta-analysis

BACKGROUND

There is still an ongoing discussion on the prognostic value of cystatin C in assessment of kidney function. Accordingly, the present study aimed to conduct a meta-analysis to provide evidence for the prognostic value of this biomarker for acute kidney injury (AKI) in children.

METHODS

An extensive search was performed in electronic databases of Medline, Embase, ISI Web of Science, Cochrane library and Scopus until the end of 2015. Standardized mean difference (SMD) with a 95% of confidence interval (95% CI) and the prognostic performance characteristics of cystatin C in prediction of AKI were assessed. Analyses were stratified based on the sample in which the level of cystatin C was measured (serum vs. urine).

RESULTS

A total of 24 articles were included in the meta-analysis [1948 children (1302 non-AKI children and 645 AKI cases)]. Serum (SMD = 0.96; 95% CI: 0.68-1.24; p < 0.0001) and urine (SMD = 0.54; 95% CI:0.34-0.75; p < 0.0001) levels of cystatin C were significantly higher in children with AKI. Overall area under the curve of serum cystatin C and urine cystatin C in prediction of AKI were 0.83 (95% CI: 0.80-0.86) and 0.85 (95% CI: 0.81-0.88), respectively. The best sensitivity (value = 0.85; 95% CI: 0.78-0.90) and specificity (value = 0.61; 95% CI: 0.48-0.73), were observed for the serum concentration of this protein and in the cut-off points between 0.4-1.0 mg/L.

CONCLUSION

The findings of the present study showed that cystatin C has an acceptable prognostic value for prediction of AKI in children. Since the serum level of cystatin C rises within the first 24 h of admission in patients with AKI, this biomarker can be a suitable alternative for traditional diagnostic measures.

Biomarkers for the Early Detection and Prognosis of Acute Kidney Injury

AKI is an increasingly common disorder that is strongly linked to short- and long-term morbidity and mortality. Despite a growing heterogeneity in its causes, providing a timely and certain diagnosis of AKI remains challenging. In this review, we summarize the evolution of AKI biomarker studies over the past few years, focusing on two major areas of investigation: the early detection and prognosis of AKI. We highlight some of the lessons learned in conducting AKI biomarker studies, including ongoing attempts to address the limitations of creatinine as a reference standard and the recent shift toward evaluating the prognostic potential of these markers. Lastly, we suggest current gaps in knowledge and barriers that may be hindering their incorporation into care and a full ascertainment of their value.

Associations between urinary kidney injury biomarkers and cardiovascular mortality risk in elderly men with diabetes

AIM

Three urinary biomarkers, kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and cystatin C, have been suggested as clinically relevant highly specific biomarkers of acute kidney tubular damage. Yet, the utility of these biomarkers in the prognostication of diabetic nephropathy has been less studied. Therefore, we aimed to investigate the longitudinal association between these urinary biomarkers and cardiovascular mortality in patients with diabetes.

METHODS

The study sample consisted of participants with diabetes in the community-based Uppsala Longitudinal Study of Adult Men (n = 91; mean age 77.8 years). During follow-up (median 8.3 years, interval 0.7-13.4 years), 33 participants died of cardiovascular causes.

RESULTS

In a multivariable Cox regression model adjusting for age, glomerular filtration rate, and urinary albumin/creatinine ratio, higher urinary KIM-1/creatinine was associated with an increased risk for cardiovascular mortality (HR per SD increase 1.51, 95% confidence intervals 1.03-2.24, P = 0.03). Neither urinary NGAL/creatinine nor urinary cystatin C/creatinine were independently associated with an increased cardiovascular mortality risk.

CONCLUSION

In elderly men with diabetes, higher urinary KIM-1/creatinine was associated with an increased long-term risk of cardiovascular mortality independently of established markers of diabetic nephropathy. Our data provide support for kidney tubular damage as an important aspect of diabetic nephropathy that merits further investigation.

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

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

Peri-operative renal dysfunction: prevention and management

Postoperative increases in serum creatinine concentration, by amounts historically viewed as trivial, are associated with increased morbidity and mortality. Acute kidney injury is common, affecting one in five patients admitted with acute medical disease and up to four in five patients admitted to intensive care, of whom one in two have had operations. This review is focused principally on the identification of patients at risk of acute kidney injury and the prevention of injury. In the main, there are no interventions that directly treat the damaged kidney. The management of acute kidney injury is based on correction of dehydration, hypotension, and urinary tract obstruction, stopping nephrotoxic drugs, giving antibiotics for bacterial infection, and commencing renal replacement therapy if necessary.

Novel biomarkers for early diagnosis of acute kidney injury after cardiac surgery in adults

Acute kidney injury after cardiac surgery with cardiopulmonary bypass is a common and serious complication and it is associated with increased morbidity and mortality. Diagnosis of acute kidney injury is based on the serum creatinine levels which rise several hours to days after the initial injury. Thus, novel biomarkers that will enable faster diagnosis are needed in clinical practice. There are numerous urine and serum proteins that indicate kidney injury and are under extensive research. Despite promising basic research results and assembled data, which indicate superiority of some biomarkers to creatinine, we are still awaiting clinical application.

Comparison of Plasma and Urine Biomarker Performance in Acute Kidney Injury

Background

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

Methods

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

Results

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

Conclusions

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

Urine Biomarkers and Perioperative Acute Kidney Injury: The Impact of Preoperative Estimated GFR

BACKGROUND

The interaction between baseline kidney function and the performance of biomarkers of acute kidney injury (AKI) on the development of AKI is unclear.

STUDY DESIGN

Post hoc analysis of prospective cohort study.

SETTING & PARTICIPANTS

The 1,219 TRIBE-AKI Consortium adult cardiac surgery cohort participants.

PREDICTOR

Unadjusted postoperative urinary biomarkers of AKI measured within 6 hours of surgery.

OUTCOME

AKI was defined as AKI Network stage 1 (any AKI) or higher, as well as a doubling of serum creatinine level from the preoperative value or the need for post-operative dialysis (severe AKI).

MEASUREMENTS

Stratified analyses by preoperative estimated glomerular filtration rate (eGFR) ≤ 60 versus > 60mL/min/1.73m(2).

RESULTS

180 (42%) patients with preoperative eGFRs≤60mL/min/1.73m(2) developed clinical AKI compared with 246 (31%) of those with eGFRs>60mL/min/1.73m(2) (P<0.001). For log2-transformed biomarker concentrations, there was a significant interaction between any AKI and baseline eGFR for interleukin 18 (P=0.007) and borderline significance for liver-type fatty acid binding protein (P=0.06). For all biomarkers, the adjusted relative risk (RR) point estimates for the risk for any AKI were higher in those with elevated baseline eGFRs compared with those with eGFRs≤60mL/min/1.73m(2). However, the difference in magnitude of these risks was low (adjusted RRs were 1.04 [95% CI, 0.99-1.09] and 1.11 [95% CI, 1.07-1.15] for those with preoperative eGFRs≤60mL/min/1.73m(2) and those with higher eGFRs, respectively). Although no biomarker displayed an interaction for baseline eGFR and severe AKI, log2-transformed interleukin 18 and kidney injury molecule 1 had significant adjusted RRs for severe AKI in those with and without baseline eGFRs≤60mL/min/1.73m(2).

LIMITATIONS

Limited numbers of patients with severe AKI and post-operative dialysis.

CONCLUSIONS

The association between early postoperative AKI urinary biomarkers and AKI is modified by preoperative eGFR. The degree of this modification and its impact on the biomarker-AKI association is small across biomarkers. Our findings suggest that distinct biomarker cutoffs for those with and without a preoperative eGFR≤60mL/min/1.73m(2) is not necessary.

Plasma IL-6 and IL-10 Concentrations Predict AKI and Long-Term Mortality in Adults after Cardiac Surgery

Inflammation has an integral role in the pathophysiology of AKI. We investigated the associations of two biomarkers of inflammation, plasma IL-6 and IL-10, with AKI and mortality in adults undergoing cardiac surgery. Patients were enrolled at six academic centers (n = 960). AKI was defined as a ≥ 50% or ≥ 0.3-mg/dl increase in serum creatinine from baseline. Pre- and postoperative IL-6 and IL-10 concentrations were categorized into tertiles and evaluated for associations with outcomes of in-hospital AKI or postdischarge all-cause mortality at a median of 3 years after surgery. Preoperative concentrations of IL-6 and IL-10 were not significantly associated with AKI or mortality. Elevated first postoperative IL-6 concentration was significantly associated with higher risk of AKI, and the risk increased in a dose-dependent manner (second tertile adjusted odds ratio [OR], 1.61 [95% confidence interval (95% CI), 1.10 to 2.36]; third tertile adjusted OR, 2.13 [95% CI, 1.45 to 3.13]). First postoperative IL-6 concentration was not associated with risk of mortality; however, the second tertile of peak IL-6 concentration was significantly associated with lower risk of mortality (adjusted hazard ratio, 0.75 [95% CI, 0.57 to 0.99]). Elevated first postoperative IL-10 concentration was significantly associated with higher risk of AKI (adjusted OR, 1.57 [95% CI, 1.04 to 2.38]) and lower risk of mortality (adjusted HR, 0.72 [95% CI, 0.56 to 0.93]). There was a significant interaction between the concentration of neutrophil gelatinase-associated lipocalin, an established AKI biomarker, and the association of IL-10 concentration with mortality (P = 0.01). These findings suggest plasma IL-6 and IL-10 may serve as biomarkers for perioperative outcomes.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Urinary exosomes: a novel means to non-invasively assess changes in renal gene and protein expression

Background

In clinical practice, there is a lack of markers for the non-invasive diagnosis and follow-up of kidney disease. Exosomes are membrane vesicles, which are secreted from their cells of origin into surrounding body fluids and contain proteins and mRNA which are protected from digestive enzymes by a cell membrane.

Methods

Toxic podocyte damage was induced by puromycin aminonucleoside in rats (PAN). Urinary exosomes were isolated by ultracentrifugation at different time points during the disease. Exosomal mRNA was isolated, amplified, and the mRNA species were globally assessed by gene array analysis. Tissue-specific gene and protein expression was assessed by RT-qPCR analysis and immunohistochemistry.

Results

Gene array analysis of mRNA isolated from urinary exosomes revealed cystatin C mRNA as one of the most highly regulated genes. Its gene expression increased 7.5-fold by day 5 and remained high with a 1.9-fold increase until day 10. This was paralleled by a 2-fold increase in cystatin C mRNA expression in the renal cortex. Protein expression in the kidneys also dramatically increased with de novo expression of cystatin C in glomerular podocytes in parts of the proximal tubule and the renal medulla. Urinary excretion of cystatin C increased approximately 2-fold.

Conclusion

In this proof-of-concept study, we could demonstrate that changes in urinary exosomal cystatin C mRNA expression are representative of changes in renal mRNA and protein expression. Because cells lining the urinary tract produce urinary exosomal cystatin C mRNA, it might be a more specific marker of renal damage than glomerular-filtered free cystatin C.

Adjudication of etiology of acute kidney injury: experience from the TRIBE-AKI multi-center study

Background

Adjudication of patient outcomes is a common practice in medical research and clinical trials. However minimal data exists on the adjudication process in the setting of Acute Kidney Injury (AKI) as well as the ability to judge different etiologies (e.g. Acute Tubular Necrosis (ATN), Pre-renal Azotemia (PRA)).

Methods

We enrolled 475 consecutive patients undergoing cardiac surgery at four sites of the Translational Research Investigating Biomarker Endpoints in AKI (TRIBE-AKI) study. Three expert nephrologists performed independent chart review, utilizing clinical variables and retrospective case report forms with pre intra and post-operative data, and then adjudicated all cases of AKI (n = 67). AKI was defined as a > 50% increase in serum creatinine for baseline (RIFLE Risk). We examined the patterns of AKI diagnoses made by the adjudication panel as well as association of these diagnoses with pre and postoperative kidney injury biomarkers.

Results

There was poor agreement across the panel of reviewers with their adjudicated diagnoses being independent of each other (Fleiss’ Kappa = 0.046). Based on the agreement of the two out of three reviewers, ATN was the adjudicated diagnosis in 41 cases (61%) while PRA occurred in 13 (19%). Neither serum creatinine or any other biomarker of AKI (urine or serum), was associated with an adjudicated diagnosis of ATN within the first 24 post-operative hours.

Conclusion

The etiology of AKI after cardiac surgery is probably multi-factorial and pure forms of AKI etiologies, such as ATN and PRA may not exist. Biomarkers did not appear to correlate with the adjudicated etiology of AKI; however the lack of agreement among the adjudicators impacted these results.

Trial registration

Clinicaltrials.gov: NCT00774137

Urinary cystatin C as an early biomarker of acute kidney injury after open and endovascular abdominal aortic aneurysm repair

BACKGROUND

Acute kidney injury (AKI) after open repair (OR) and endovascular repair (EVAR) of abdominal aortic aneurysm (AAA) is associated with increased mortality and hospital costs. Early detection of AKI is critical to prevent its progression. Recent findings demonstrate that elevated levels of urinary cystatin C (uCysC) may reflect tubular dysfunction. We prospectively evaluated whether uCysC can detect renal dysfunction earlier than serum creatinine (sCr).

METHODS

In a prospective study, 126 consecutive patients (mean age ± SD, 69.1 ± 8.66 years) with AAA (EVAR = 87, OR = 39) were enrolled. sCr and uCysC were measured preoperatively (baseline) and at 6, 24, and 48 hr postoperatively. A final measurement was made on day 5. AKI was defined according to Acute Kidney Injury Network criteria.

RESULTS

The incidence of AKI was significantly higher (χ(2) test, P < 0.05) in the OR group (n = 13, 33%) than in the EVAR group (n = 15, 17%). The baseline median (interquartile range) value of uCysC was significantly higher (t-test, P < 0.05) in patients of both groups (OR-EVAR) who developed AKI from those who did not (OR/AKI group: 0.06 [0.02-0.12] mg/L, EVAR/AKI group: 0.08 [0.05-0.11] mg/L versus no-AKI subjects: 0.04 [0.02-0.07] mg/L). Subsequent analysis showed that at 6 hr postoperatively, the patients who developed AKI increased their uCysC levels significantly from baseline (OR/AKI group: 0.58 [0.42-0.70] mg/L, EVAR/AKI group: 0.59 [0.30-1.07] mg/L). The median value of uCysC in AKI patients increased at 24 hr (OR/AKI group: 1.37 [0.78-3.40] mg/L, EVAR/AKI group: 2.11 [0.70-2.42] mg/L) and peaked at 48 hr (OR/AKI group: 6.16 [1.74-10.73] mg/L, EVAR/AKI group: 2.57 [1.21-7.40] mg/L), while no increase was observed among those who did not develop AKI at the same time points (0.06 [0.04-0.14] vs. 0.08 [0.04-0.19] mg/L). The diagnostic accuracy of uCysC at 6 hr post-surgery was excellent (area under the curve - receiver-operating characteristic [AUC-ROC] = 0.968), significantly higher than sCr (AUC-ROC = 0.844) and a cutoff value set at 0.30 mg/L can diagnose AKI with a sensitivity of 85.71% and a specificity of 98.97%.

CONCLUSIONS

uCysC is superior to sCr in the early diagnosis of AKI following open and endovascular AAA repair.

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.