Early detection of acute renal failure by serum cystatin C

SDMA is an early marker of change in GFR after living-related kidney donation

BACKGROUND

Early detection of changes in the glomerular filtration rate (GFR) is crucial in detecting acute kidney injury. There is burgeoning evidence from preclinical and clinical studies that symmetrical dimethylarginine (SDMA) correlates well with different parameters of renal function. In some studies, SDMA even outperformed creatinine as a marker of GFR. It is however unknown how fast SDMA is increasing after reduction in GFR. The aim of our study was therefore to determine the temporal change of SDMA in comparison with cystatin C after a defined reduction in GFR.

METHODS

Blood samples from 24 healthy living-related kidney donors (19 F/5 M), mean age 55.2 ± 8.3 years, were collected prior to donation of the kidney as well as 1, 6, 12, 24, 72 and 168 h after unilateral nephrectomy. SDMA levels were measured using a liquid chromatography-mass spectrometry-based method.

RESULTS

Within 6 h after unilateral nephrectomy, i.e. reduction of GFR by 50%, SDMA rose from 0.571 ± 0.120 to 0.659 ± 0.135 µmol/L (P < 0.001). Baseline cystatin C levels increased from 0.87 ± 0.16 to 1.07 ± 0.15 mg/L (P < 0.001). Also, serum creatinine rose significantly within 6 h after removal of one kidney from 65.4 ± 8.4 to 88.8 ± 10.2 µmol/L (P < 0.001).

DISCUSSION

SDMA might be a valuable and early marker of change in GFR in the clinical and experimental setting. Future studies will have to clarify whether sensitivity, specificity and temporal resolution of SDMA make it an attractive candidate for the assessment of renal function in both the experimental and clinical setting.

Cystatin C as a marker of acute kidney injury in the emergency department

BACKGROUND AND OBJECTIVES

The diagnosis of acute kidney injury (AKI) is usually based on changes in serum creatinine, which is a poor marker of early renal dysfunction. The discriminative and predictive abilities of serum and urinary cystatin C were examined for the prediction of AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this prospective cohort study, serum and urinary cystatin C were serially measured in a heterogeneous group of patients (n = 616) presenting to a tertiary care emergency department. The primary outcome was AKI, classified according to RIFLE and AKIN criteria. The secondary outcome was an adjudication based on clinical criteria to AKI, prerenal azotemia, chronic kidney disease (CKD), and normal kidney function.

RESULTS

Patients were adjudicated to have AKI in 21.1%, prerenal azotemia in 25.8%, CKD in 2.4%, and normal kidney function in 50.7%. For the diagnosis of AKI, the discriminatory ability of urinary creatinine and cystatin C was marginal. Both serum cystatin C and serum creatinine (at presentation and 6 hours later) showed high discriminatory ability for the diagnosis of AKI. However, only serum cystatin C attained a significant early predictive power (Hosmer-Lemeshow P value > 0.05). Serum cystatin C could differentiate between AKI and prerenal azotemia, but not between AKI and CKD.

CONCLUSIONS

Serum cystatin C is an early, predictive biomarker of AKI, which outperforms serum creatinine in the heterogeneous emergency department setting. However, neither biomarker discriminated between AKI and CKD. Additional biomarkers continue to be needed for improved specificity in the diagnosis of community-acquired AKI.

Elevated urinary IL-18 levels at the time of ICU admission predict adverse clinical outcomes

BACKGROUND AND OBJECTIVES

Urine IL-18 (uIL-18) has demonstrated moderate capacity to predict acute kidney injury (AKI) and adverse outcomes in defined settings. Its ability to predict AKI and provide prognostic information in broadly selected, critically ill adults remains unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The study prospectively evaluated the capacity of uIL-18 measured within 24 hours of intensive care unit (ICU) admission to predict AKI, death, and receipt of acute dialysis in a large mixed-adult ICU population.

RESULTS

Of 451 patients, 86 developed AKI within 48 hours of enrollment and had higher median uIL-18 levels [426 (interquartile range [IQR]: 152 to 1183) pg/mg creatinine] compared with those without AKI [248 (IQR: 120 to 559) pg/mg]. The area under the receiver operating characteristic curve for uIL-18 predicting subsequent AKI within 24 hours was 0.62 (95% CI: 0.54 to 0.69) and improved modestly to 0.67 (95% CI: 0.53 to 0.81) in patients whose enrollment eGFR was >or=75 ml/min per 1.73 m(2). The highest median uIL-18 levels were observed in patients with sepsis at enrollment [508 (IQR: 230 to 1281) pg/mg], those receiving acute dialysis [571 (IQR: 161 to 1614) pg/mg] or dying [532 (IQR: 210 to 1614) pg/mg] within 28 days of ascertainment. After adjustment for a priori selected clinical predictors, uIL-18 remained independently predictive of composite outcome of death or acute dialysis within 28 days of ascertainment (odds ratio, 1.86 [95% CI: 1.31 to 2.64]).

CONCLUSIONS

uIL-18 did not reliably predict AKI development, but did predict poor clinical outcomes in a broadly selected, critically ill adult population.

Serum cystatin C is an early predictive biomarker of acute kidney injury after pediatric cardiopulmonary bypass

BACKGROUND AND OBJECTIVES

Acute kidney injury (AKI) is a frequent complication of cardiopulmonary bypass (CPB). Serum creatinine (SCr), the current standard, is an inadequate marker for AKI since a delay occurs before SCr rises. Biomarkers that are sensitive and rapidly measurable could allow early intervention and improve patient outcomes. We investigated the value of serum cystatin C as an early biomarker for AKI after pediatric CPB.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We analyzed data from 374 prospectively enrolled children undergoing CPB. Serum samples were obtained before and at 2, 12, and 24 hours after CPB. Cystatin C was quantified by nephelometry. The primary outcome was AKI, defined as a > or =50% increase in SCr. Secondary outcomes included severity and duration of AKI, hospital length of stay, and mortality. A multivariable stepwise logistic regression analysis was used to assess predictors of AKI.

RESULTS

One hundred nineteen patients (32%) developed AKI using SCr criteria. Serum cystatin C concentrations were significantly increased in AKI patients at 12 hours after CPB (P < 0.0001) and remained elevated at 24 hours (P < 0.0001). Maximal sensitivity and specificity for prediction of AKI occurred at a 12-hour cystatin C cut-off of 1.16 mg/L. The 12-hour cystatin C strongly correlated with severity and duration of AKI as well as length of hospital stay. In multivariable analysis, 12-hour cystatin C remained a powerful independent predictor of AKI.

CONCLUSION

Serum cystatin C is an early predictive biomarker for AKI and its clinical outcomes after pediatric CPB.

An Official ATS/ERS/ESICM/SCCM/SRLF Statement: Prevention and Management of Acute Renal Failure in the ICU Patient: an international consensus conference in intensive care medicine

OBJECTIVES

To address the issues of Prevention and Management of Acute Renal Failure in the ICU Patient, using the format of an International Consensus Conference.

METHODS AND QUESTIONS

Five main questions formulated by scientific advisors were addressed by experts during a 2-day symposium and a Jury summarized the available evidence: (1) Identification and definition of acute kidney insufficiency (AKI), this terminology being selected by the Jury; (2) Prevention of AKI during routine ICU Care; (3) Prevention in specific diseases, including liver failure, lung Injury, cardiac surgery, tumor lysis syndrome, rhabdomyolysis and elevated intraabdominal pressure; (4) Management of AKI, including nutrition, anticoagulation, and dialysate composition; (5) Impact of renal replacement therapy on mortality and recovery.

RESULTS AND CONCLUSIONS

The Jury recommended the use of newly described definitions. AKI significantly contributes to the morbidity and mortality of critically ill patients, and adequate volume repletion is of major importance for its prevention, though correction of fluid deficit will not always prevent renal failure. Fluid resuscitation with crystalloids is effective and safe, and hyperoncotic solutions are not recommended because of their renal risk. Renal replacement therapy is a life-sustaining intervention that can provide a bridge to renal recovery; no method has proven to be superior, but careful management is essential for improving outcome.

Plasma cystatin C and acute kidney injury after cardiopulmonary bypass

BACKGROUND AND OBJECTIVES

Little is known about the performance of plasma cystatin C (CysC) in patients undergoing cardiopulmonary bypass (CPB) and its utility in the early diagnosis of acute kidney injury (AKI). In this post hoc analysis, the goal was to determine whether plasma cystatin C, measured 2 hours after the conclusion of CPB, is a reliable marker of AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Plasma CysC was measured in 150 patients undergoing CPB at the following times: preoperatively, 2 hours after the conclusion of CPB, postoperative day 1, and postoperative day 2. Plasma CysC levels were related to the development of AKI as defined by an increase in serum creatinine of >or=50% or >or=0.3 mg/dl from baseline up to 3 days postoperative. Mixed linear models were used to evaluate the relationship of serial plasma CysC values with AKI. The discriminatory capacity of plasma CysC was estimated using receiver operating characteristic curves. Logistic regression was utilized to assess the adjusted relationship between plasma CysC and subsequent AKI.

RESULTS

AKI developed in 47 (31.3%) patients. Plasma CysC was higher at all times among patients who developed AKI compared with those who did not (P < 0.0001). The discriminatory capacity of plasma CysC measured preoperatively and 2 hours after the conclusion of CPB was modest.

CONCLUSIONS

Serial measures of plasma CysC are highly correlated with the development of AKI. However, the discriminatory capacity of plasma CysC as an early marker of AKI remains limited.

Tubular proteinuria in acute kidney injury: a critical evaluation of current status and future promise

The diagnosis and prognosis of acute kidney injury (AKI) by current clinical means is inadequate. Biomarkers of kidney injury that are easily measured and unaffected by physiological variables could revolutionize the management of AKI. Our objective was to systematically review the diagnostic and prognostic utility of urine and serum biomarkers of AKI in humans. We searched MEDLINE, PubMed and EMBASE databases (January 2000–August 2009) for biomarker studies that could be classified into the following categories: (a) confirmation of the diagnosis of established AKI, (b) early prediction of AKI, and (c) prognostication of AKI. We identified 54 manuscripts published since 2000 that met our inclusion and exclusion criteria. Urinary interleukin-18 (IL-18), kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL) and N-acetyl- β-d-glucosaminidase (NAG) are potentially useful biomarkers for the diagnosis of established AKI. Urinary NGAL, IL-18, and liver-type fatty acid binding protein, and serum NGAL and cystatin C represent the most promising biomarkers for early prediction of AKI. Urinary cystatin C, α1-microglobulin, NAG and retinol-binding protein may be useful to predict severity and outcomes of AKI. In conclusion, we identified several studies of promising biomarkers for the diagnosis, prediction and prognostication of AKI. However, we note several limitations, including small sample sizes, inadequate gold standard, exclusion of patients with chronic kidney disease, incomplete statistical analyses, utilization of research-based assays and a paucity of studies examining prediction for clinical outcomes. Future studies will need to address these limitations in order for further progress to be made.

Urinary cystatin C is diagnostic of acute kidney injury and sepsis, and predicts mortality in the intensive care unit

Introduction

To evaluate the utility of urinary cystatin C (uCysC) as a diagnostic marker of acute kidney injury (AKI) and sepsis, and predictor of mortality in critically ill patients.

Methods

This was a two-center, prospective AKI observational study and post hoc sepsis subgroup analysis of 444 general intensive care unit (ICU) patients. uCysC and plasma creatinine were measured at entry to the ICU. AKI was defined as a 50% or 0.3-mg/dL increase in plasma creatinine above baseline. Sepsis was defined clinically. Mortality data were collected up to 30 days. The diagnostic and predictive performances of uCysC were assessed from the area under the receiver operator characteristic curve (AUC) and the odds ratio (OR). Multivariate logistic regression was used to adjust for covariates.

Results

Eighty-one (18%) patients had sepsis, 198 (45%) had AKI, and 64 (14%) died within 30 days. AUCs for diagnosis by using uCysC were as follows: sepsis, 0.80, (95% confidence interval (CI), 0.74 to 0.87); AKI, 0.70 (CI, 0.64 to 0.75); and death within 30 days, 0.64 (CI, 0.56 to 0.72). After adjustment for covariates, uCysC remained independently associated with sepsis, AKI, and mortality with odds ratios (CI) of 3.43 (2.46 to 4.78), 1.49 (1.14 to 1.95), and 1.60 (1.16 to 2.21), respectively. Concentrations of uCysC were significantly higher in the presence of sepsis (P < 0.0001) or AKI (P < 0.0001). No interaction was found between sepsis and AKI on the uCysC concentrations (P = 0.53).

Conclusions

Urinary cystatin C was independently associated with AKI, sepsis, and death within 30 days.

Trial registration

Australian New Zealand Clinical Trials Registry ACTRN012606000032550.

Neutrophil gelatinase-associated lipocalin: a promising biomarker for detecting cardiac surgery-associated acute kidney injury

Acute kidney injury is a common and significant problem that occurs in a wide variety of clinical settings. Cardiac surgery-associated acute kidney injury continues to be a well-recognized complication of cardiac surgery with associated morbidity and mortality. A lack of early biomarkers for acute kidney injury has prevented timely interventions to mitigate the effects of acute kidney injury. Because serum creatinine is not a timely marker of acute kidney injury, it cannot be used to institute potentially effective therapies to treat acute kidney injury in patients during phases when the injury is still potentially reversible. Neutrophil gelatinase-associated lipocalin has been identified as a promising biomarker for early detection of acute kidney injury. Several studies have shown that neutrophil gelatinase-associated lipocalin levels increase significantly in patients with acute kidney injury 24 to 48 hours before an increase in serum creatinine is detectable. Recent studies suggest that measurements of neutrophil gelatinase-associated lipocalin levels in patients at risk for cardiac surgery-associated acute kidney injury can facilitate its early diagnosis and allow clinicians to implement therapeutic adjustments that have the potential to reverse renal cellular damage and minimize further kidney injury.

Cystatin C and contrast-induced acute kidney injury

BACKGROUND

Cystatin C (CyC) is more sensitive than serum creatinine (sCr) to rapidly detect acute changes in renal function.

METHODS AND RESULTS

We measured CyC together with sCr in 410 consecutive patients with chronic kidney disease undergoing either coronary and/or peripheral angiography and/or angioplasty. sCr was assessed at baseline and 24 and 48 hours after contrast media exposure. CyC was assessed at baseline and at 24 hours. Major adverse events (including death of any cause and dialysis) at 12 months were assessed. At 48 hours after contrast media exposure, contrast-induced acute kidney injury (defined as a sCr increase > or =0.3 mg/dL) occurred in 34 patients (8.2%). A CyC increase concentration > or =10% at 24 hours after contrast media exposure was detected in 87 patients (21.2%). This was the best CyC cutoff for the early identification of patients at risk for contrast-induced acute kidney injury (negative predictive value=100%; positive predictive value=39.1%). According to the defined cutoffs (that is, increase in CyC > or =10% and sCr > or =0.3 mg/dL), major adverse events occurred in 16 of 297 patients (5.4%) without any cutoffs satisfied (group 1), in 9 of 49 patients (18.4%) with only a CyC increase > or =10% (group 2), and in 9 of 31 patients (29%) with both cutoffs satisfied (group 3). By logistic regression analysis, the independent predictors of major adverse events at 1 year were group 2 (odds ratio=2.52; 95% confidence interval, 1.17 to 5.41; P=0.02), group 3 (odds ratio=4.45; 95% confidence interval, 1.72 to 11.54; P=0.002), and baseline glomerular filtration rate (odds ratio=0.91; 95% confidence interval, 0.88 to 0.95; P<0.001).

CONCLUSIONS

In patients with chronic kidney disease, CyC seems to be a reliable marker for the early diagnosis and prognosis of contrast-induced acute kidney injury.

Rapid detection of acute kidney injury by plasma cystatin C in the intensive care unit

BACKGROUND

Plasma cystatin C (pCysC) has been proposed as an alternative to plasma creatinine (pCr) as a measure of renal function. We compared the detection of functional change by both biomarkers in critically ill patients.

METHODS

pCysC and pCr were measured on admission to one of two intensive care units (ICU) and then daily over 7 days. Patients were classified according to the analyte that first increased by either ≥25 or ≥50% above the admission value. The proportion of patients in each class was compared using McNemar's chi-square test. Sustained acute kidney injury (AKI, a ≥50% increase in pCr from baseline for ≥24 h), dialysis and death within 30 days were recorded. The ability of pCysC and pCr on admission to predict sustained AKI, dialysis or death was assessed from the area under the receiver operator characteristic curve (AUC).

RESULTS

Of 442 patients, 83 had a ≥50% increase in one analyte, 17 in both and 342 in neither. Comparable numbers for a ≥25% increase were 163 in one analyte, 45 in both and 234 in neither. pCysC increased prior to pCr more frequently than vice versa in both the cohort with a ≥50% increase (P < 0.0001) and with a ≥25% increase (P < 0.0001). pCysC predicted sustained AKI with an AUC of 0.80 [95% confidence interval (CI) = 0.71-0.88]. pCysC and pCr were similarly moderately predictive of death or dialysis with AUCs of 0.61 [95% CI = 0.53-0.68] and 0.60 [95% CI = 0.51-0.67], respectively.

CONCLUSION

pCysC was an effective and earlier surrogate marker of decreased renal function than pCr in a general ICU population.

Acute kidney injury in elderly persons

The incidence rate of acute kidney injury (AKI) is highest in elderly patients, who make up an ever-growing segment of the population at large. AKI in these patients is associated with an increased risk of short- and long-term death and chronic kidney disease, including end-stage renal disease. Whether AKI in older individuals carries a larger relative risk for these outcomes compared with younger individuals is unclear at this time. Other domains, such as health-related quality of life, may be mildly impacted on after an episode of AKI. No effective therapies for AKI currently are available for widespread use. However, because the incidence of AKI is highest in the elderly and the phenotype is not discernibly different from AKI in all populations, future randomized controlled trials of interventions for AKI should be performed in the elderly population.

Serum cystatin C in elderly cardiac surgery patients

BACKGROUND

Elderly cardiac surgery patients are more prone to develop postoperative acute kidney injury (AKI). The common clinical glomerular filtration marker, plasma creatinine, is considered to be inadequate to discover AKI in its early stage. The aim of this study was to determine if serum cystatin C can detect mild renal failure earlier than plasma creatinine.

METHODS

From 110 cardiac surgery patients aged 70 or greater years, serum cystatin C and plasma creatinine samples were collected preoperatively and on postoperative days 1 to 5. Their urine output, creatinine, and estimated glomerular filtration rate were calculated and AKI was determined by the risk-injury-failure-loss-end-stage kidney disease criteria (RIFLE). The correlation of plasma creatinine and serum cystatin C to AKI was calculated.

RESULTS

After cardiac surgery, 62 of the 110 patients (56.4%) developed AKI according to the RIFLE classification. In this group, both serum cystatin C and plasma creatinine peaked on postoperative day 3. Cystatin C and creatinine correlated equally with AKI at different time points calculated with receiver operating characteristic curves. On postoperative day 1 the area under the curve (AUC) for creatinine was 0.66 (0.55 to 0.76) and for cystatin C 0.71 (0.61 to 0.81); Delta AUC 0.05 (0.01 to 0.12), p = 0.11. On postoperative day 2 the AUC for creatinine was 0.74 (0.64 to 0.83) and for cystatin was C 0.77 (0.68 to 0.86); Delta AUC -0.03 (-0.09 to 0.03), p = 0.32.

CONCLUSIONS

Elderly cardiac surgery patients have a high incidence of AKI, as defined by the RIFLE criteria. After cardiac surgery serum cystatin C and plasma creatinine detected AKI similarly.

Renal dysfunction in chronic liver disease

This article is one of ten reviews selected from the Yearbook of Intensive Care and Emergency Medicine 2010 (Springer Verlag) and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/yearbook. Further information about the Yearbook of Intensive Care and Emergency Medicine is available from http://www.springer.com/series/2855.

Impact of the interval between coronary angiography and off-pump coronary bypass surgery on postoperative renal function

Background

Postoperative acute kidney injury (AKI) is a significant complication after coronary artery bypass surgery. Prior coronary angiography increases the likelihood of AKI due to the use of a radiocontrast dye. This study examined the effect of coronary angiography on the postoperative renal function after off-pump coronary artery bypass surgery (OPCAB).

Methods

The records of 110 patients who required OPCAB were reviewed. These patients also had at least two of the following conditions: chronic kidney disease, hypertension, diabetes mellitus, emergency surgery, congestive heart failure, age >75 years, hematocrit <30%, a left ventricular ejection fraction <40%, or the use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers. The patients were divided into two groups; coronary angiography performed within two days of OPCAB (Control group, n = 55), and coronary angiography performed more than two days before OPCAB (Angio group, n = 55). The serum creatinine (SCr) and serum cystatin C levels were measured on the day before surgery, as well as on postoperative days 1, 2, 3 and 7. The estimated glomerular filtration rate (eGFR) was also obtained on those days. AKI was defined as an increase in Cr ≥50% or ≥0.3 mg/dl within 48 hours.

Results

The postoperative changes in the SCr, cystatin C and eGFR were similar in the two groups. The incidence of AKI and renal replacement therapy were similar in the two groups.

Conclusions

Coronary angiography performed within two days of OPCAB does not affect the postoperative renal function.

Acute kidney injury in ST-segment elevation acute myocardial infarction complicated by cardiogenic shock at admission

OBJECTIVE

To evaluate the clinical and prognostic relevance of acute kidney injury (AKI) in the setting of ST-elevation acute myocardial infarction (STEMI) complicated by cardiogenic shock (CS).

DESIGN

Prospective study.

SETTING

Single-center study, 13-bed intensive cardiac care unit at a University Cardiological Center.

PATIENTS

Ninety-seven consecutive STEMI patients with CS at admission, undergoing intra-aortic balloon pump (IABP) support and primary percutaneous coronary intervention (PCI).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We measured serum creatinine at baseline and each day for the following 3 days. Acute kidney injury was defined as a rise in creatinine >25% from baseline. Overall, AKI occurred in 52 (55%) patients, and in 12 of these patients, a renal replacement therapy was required. In multivariate analysis, age >75 yrs (p = .005), left ventricular ejection fraction < or = 40% (p = .009), and use of mechanical ventilation (p = .01) were independent predictors of AKI. Patients developing AKI had a longer hospital stay, a more complicated clinical course, and significantly higher mortality rate (50% vs. 2.2%; p <.001) than patients without AKI. In our population, AKI was the strongest independent predictor of in-hospital mortality (relative risk 12.3, 95% confidence intervals 1.78 to 84.9; p <.001).

CONCLUSIONS

In patients with STEMI complicated by CS, AKI represents a frequent clinical complication associated with a poor prognosis.

Should kidney tubular markers be adjusted for urine creatinine? The example of urinary cystatin C

BACKGROUND

Evaluation of specific urinary markers with respect to urine creatinine (uCreat) is common. However, as uCreat is a function of both glomerular filtration and tubular secretion, using uCreat for specific tubular markers, suggests that glomerular function is normal, and there is no tubular secretion. Thus, adjusting values of any tubular marker to uCreat, especially in patients with acute or even moderate chronic renal failure, can be misleading.

METHODS

Using urine cystatin-C (uCST3) as a model tubular marker for following 120 kidney graft recipients daily, we evaluated the utility of either uCST3 alone or the uCST3/uCreat ratio to detect tubular damage. All positive kidney biopsies were always associated with a uCST3>0.18 mg/L.

RESULTS

Using the uCST3/uCreat ratio, discrepancies regarding biopsy status were observed in nine patients (4 false positive, 5 false negative results). In two patients, variability of uCreat appeared to be the most important factor causing inconsistent uCST3/uCreat ratios. With a negative predictive value (NPV) of 85.7%, uCST3/uCreat can lead to errors in clinical interpretation. These errors can be avoided when estimates of tubular damage are based on uCST3 concentrations alone (NPV=100%).

CONCLUSIONS

We recommend using the uCST3 value to evaluate the extent of renal tubular damage. Indeed, our conflicting results on uCST3/uCreat can be extended to every marker of tubular function. Evaluating a urine marker specific for renal tubular damage to a second urine marker that is itself strongly dependent upon glomerular or other renal or non-renal conditions, impairs its clinical relevance and may lead to incorrect interpretations. Correction with uCreat can be performed only in pure glomerulopathy, when specific markers of glomerular function are measured (i.e., urinary albumin). In all other cases of renal diseases, such correction is inappropriate and should be avoided. Clin Chem Lab Med 2009;47:1553-6.

Uremic toxins in acute kidney injury

Acute kidney injury (AKI) is a serious and frequent condition which may fully resolve but is associated with markedly increased mortality. Mortality in AKI is caused by nonrenal, distant organ failure. Renal recovery from AKI is often not achieved on account of new injuries in the repair phase. Uremic toxins may be the missing link between AKI and nonrenal organ failure, tubular and endothelial injury. Compared with chronic kidney disease (CKD), research of uremic toxins in AKI is in its infancy. This review presents the current knowledge on uremic toxins in AKI which is predominately derived from experimental studies. Most uremic toxins investigated have previously been identified in CKD. The review focuses on those uremic toxins with biologic effect on the respective nonrenal organs failing in AKI and on the renal tubule and the endothelium. These uremic toxins may insofar be specific mediators of pathophysiological processes in AKI.

Biomarkers in renal transplantation ischemia reperfusion injury

Ischemia reperfusion injury (IRI) is a choreographed process leading to delayed graft function (DGF) and reduced long-term patency of the transplanted organ. Early identification of recipients of grafts at risk would allow modification of the posttransplant management, and thereby potentially improve short- and long-term outcomes. The recently emerged "omics" technologies together with bioinformatics workup have allowed the integration and analysis of IRI-associated molecular profiles in the context of DGF. Such a systems biological approach promises qualitative information about interdependencies of complex processes such as IRI regulation, rather than offering descriptive tables of differentially regulated features on a transcriptome, proteome, or metabolome level leaking the functional, biological framework. In deceased-donor kidney transplantation as the primary causative factor resulting in IRI and DGF, a distinct signature and choreography of molecular events in the graft before harvesting seems to be associated with subsequent DGF. A systems biological assessment of these molecular changes suggests that processes along inflammation are of pivotal importance for the early stage of IRI. The causal proof of this association has been tested by a double-blinded, randomized, controlled trial of steroid or placebo infusion into deceased donors before the organs were harvested. Thorough systems biological analysis revealed a panel of biomarkers with excellent discrimination. In summary, integrated analysis of omics data has brought forward biomarker candidates and candidate panels that promise early assessment of IRI. However, the clinical utility of these markers still needs to be established in prospective trials in independent patient populations.

Impact of biomarker development on drug safety assessment

Drug safety has always been a key aspect of drug development. Recently, the Vioxx case and several cases of serious adverse events being linked to high-profile products have increased the importance of drug safety, especially in the eyes of drug development companies and global regulatory agencies. Safety biomarkers are increasingly being seen as helping to provide the clarity, predictability, and certainty needed to gain confidence in decision making: early-stage projects can be stopped quicker, late-stage projects become less risky. Public and private organizations are investing heavily in terms of time, money and manpower on safety biomarker development. An illustrative and "door opening" safety biomarker success story is the recent recognition of kidney safety biomarkers for pre-clinical and limited translational contexts by FDA and EMEA. This milestone achieved for kidney biomarkers and the "know how" acquired is being transferred to other organ toxicities, namely liver, heart, vascular system. New technologies and molecular-based approaches, i.e., molecular pathology as a complement to the classical toolbox, allow promising discoveries in the safety biomarker field. This review will focus on the utility and use of safety biomarkers all along drug development, highlighting the present gaps and opportunities identified in organ toxicity monitoring. A last part will be dedicated to safety biomarker development in general, from identification to diagnostic tests, using the kidney safety biomarkers success as an illustrative example.

Cardio-renal syndromes: report from the consensus conference of the acute dialysis quality initiative

A consensus conference on cardio-renal syndromes (CRS) was held in Venice Italy, in September 2008 under the auspices of the Acute Dialysis Quality Initiative (ADQI). The following topics were matter of discussion after a systematic literature review and the appraisal of the best available evidence: definition/classification system; epidemiology; diagnostic criteria and biomarkers; prevention/protection strategies; management and therapy. The umbrella term CRS was used to identify a disorder of the heart and kidneys whereby acute or chronic dysfunction in one organ may induce acute or chronic dysfunction in the other organ. Different syndromes were identified and classified into five subtypes. Acute CRS (type 1): acute worsening of heart function (AHF–ACS) leading to kidney injury and/or dysfunction. Chronic cardio-renal syndrome (type 2): chronic abnormalities in heart function (CHF-CHD) leading to kidney injury and/or dysfunction. Acute reno-cardiac syndrome (type 3): acute worsening of kidney function (AKI) leading to heart injury and/or dysfunction. Chronic reno-cardiac syndrome (type 4): chronic kidney disease leading to heart injury, disease, and/or dysfunction. Secondary CRS (type 5): systemic conditions leading to simultaneous injury and/or dysfunction of heart and kidney. Consensus statements concerning epidemiology, diagnosis, prevention, and management strategies are discussed in the paper for each of the syndromes.

Plasma neutrophil gelatinase-associated lipocalin is an early biomarker for acute kidney injury in an adult ICU population

Purpose

Neutrophil gelatinase-associated lipocalin (NGAL) is a useful marker for acute kidney injury (AKI), particularly when the timing of renal insult is known. However, its performance in an adult critical care setting has not been well described. We performed this study to estimate the diagnostic accuracy of plasma NGAL for early detection of AKI and need for renal replacement therapy (RRT) in an adult intensive care unit (ICU).

Methods

We enrolled 307 consecutive adult patients admitted to a general medical-surgical ICU; 301 were included in the final analysis. Serial blood samples were analyzed for plasma NGAL using a standardized clinical platform. The primary outcome was AKI, defined as an increase in creatinine of at least 50% from baseline or a reduction in urine output to <0.5 ml/kg/h for >6 h.

Results

Of 301 patients, 133 (44%) had AKI during their ICU stay. Plasma NGAL was a good diagnostic marker for AKI development within the next 48 h (area under ROC 0.78, 95% CI 0.65–0.90), and for RRT use (area under ROC 0.82, 95% CI 0.70–0.95). Peak plasma NGAL concentrations increased with worsening AKI severity (R = 0.554, P < 0.001).

Conclusions

Plasma NGAL is a useful early marker for AKI in a heterogeneous adult ICU population, in which the timing of renal insult is largely unknown. It allows the diagnosis of AKI up to 48 h prior to a clinical diagnosis based on AKI consensus definitions. Additionally, it predicts need for RRT and correlates with AKI severity. Early identification of high risk patients may allow potentially beneficial therapies to be initiated early in the disease process before irreversible injury occurs.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-009-1711-1) contains supplementary material, which is available to authorized users.

Contrast-induced acute kidney injury (CIAKI)

Injury to the kidney continues to occur following the administration of intravascular iodinated contrast media. In this article, the author reviews the pathophysiology of contrast-induced acute kidney injury (CIAKI), the relationship of CIAKI to long-term adverse outcomes, what type of patients are at risk of CIAKI, and how the diagnosis is made. After discussion of the reported incidence of CIAKI, an approach to prevention is briefly reviewed.

Cardiorenal syndrome: biomarkers linking kidney damage with heart failure

All the vital organs of the body share information by virtue of various biological mediators. Primary pathology of a major organ can lead to dysfunction of the other. Cardiorenal syndrome is an important example of such organ crosstalk. Primary dysfunction of the heart or kidney can lead to injury of the other organ. As molecular injury occurs prior to clinical dysfunction, effective interventions can be planned if one can detect this organ dysfunction at an earlier stage by virtue of some biological markers. Such biomarkers can be substances in urine, serum, imaging maneuvers or any other quantifiable parameters. Some currently available biomarkers are not sensitive enough to provide timely diagnosis of the disorder. An important research priority is the development of newer biomarkers or a panel of biomarkers for the early diagnosis of organ dysfunction, as well as nature of injury, guidance for therapeutic interventions and prognosis. Many newer biomarkers have been studied for both heart and kidney dysfunction. This article focuses on newer biomarkers for the cardiorenal syndrome.

Evaluation of "Loss" and "End stage renal disease" after acute kidney injury defined by the Risk, Injury, Failure, Loss and ESRD classification in critically ill patients

PURPOSE

The Risk, Injury, Failure, Loss and ESRD (RIFLE) classification has been widely accepted for the definition of acute kidney injury (AKI); however, no study has described in detail the last two stages of the classification: "Loss" and "ESRD". We aim to describe and evaluate the development of "Loss" and "ESRD" in a group of critically ill patients.

METHODS

We conducted a retrospective analysis of cases prospectively collected from the Acute Physiology and Chronic Health Assessment (APACHE III) database. Subjects were consecutive critically ill patients >18 years of age admitted to three ICUs of two tertiary care academic hospitals, from January 2003 through August 2006, excluding those who denied research authorization, chronic hemodialysis therapy, kidney transplant recipients, readmissions, and admissions for less than 12 h for low risk monitoring.

RESULTS

11,644 patients were included in the study. The median age was 66 (interquartile range, 52-76), 90% were Caucasians and 54% of the patients were male. Half of the patients developed AKI, and most of the patients were in the Risk and Injury stages. From the patients that developed AKI, a total of 1,065 (19%) patients required renal replacement therapy (RRT), 415 (39%) underwent continuous renal replacement therapy (CRRT) and 650 (61%) underwent intermittent hemodialysis. A total of 281 patients on RRT did not survive hospital discharge, 97 patients progressed to "Loss", and 282 patients progressed to "ESRD". After multivariable adjustment, the progression to "ESRD" was associated with higher baseline creatinine, odds ratio (OR) 1.19 per every increase in creatinine of 0.1 mg/dl (95% CI, 1.11-1.29) P < 0.001; and less frequent use of CRRT, OR 0.18 (95% CI, 0.11-0.29) P < 0.001.

CONCLUSION

In this large retrospective study we found that almost 50% developed some form of AKI as defined by the RIFLE classification. Of these, 19% required RRT, and 4.9% progressed to "ESRD". "ESRD" was more likely in patients with elevated baseline creatinine and those treated with intermittent hemodialysis.

Assessment of glomerular filtration rate by serum cystatin C in patients undergoing coronary artery bypass grafting

BACKGROUND

Assessment of renal function in patients undergoing coronary artery bypass grafting (CABG) is important. Cystatin C has been proposed as an improved indicator of renal function. The aim of this study was to assess cystatin C as an early marker of changes in glomerular filtration rate (GFR) after CABG.

METHODS

Blood samples were collected from 61 CABG patients at different time points. Using (51)Cr-ethylenediaminetetraacetic acid ((51)Cr-EDTA) clearance as a 'gold standard', we compared the correlations and non-parametric receiver operator characteristic curves of serum cystatin C, serum creatinine and 24 h creatinine clearance (Ccr).

RESULTS

The inverse of cystatin C correlated better with (51)Cr-EDTA than those of serum creatinine and Ccr (r = 0.8578, 0.6771 and 0.6929, respectively). Cystatin C exhibited significantly superior diagnostic accuracy for detecting GFR <80 mL/min/1.73 m(2) compared with serum creatinine (P = 0.013) and Ccr (P = 0.025); for detecting GFR <60 mL/min/1.73 m(2), cystatin C had similar diagnostic accuracy to Ccr (P = 0.812) but was superior to creatinine (P = 0.033). At the best cut-off value, cystatin C had sensitivity 89% and specificity 93% for detecting GFR <80 mL/min/1.73 m(2), sensitivity 86% and specificity 96% for detecting GFR <60 mL/min/1.73 m(2).

CONCLUSIONS

Cystatin C is a better marker for detecting small temporary changes of GFR in CABG patients. This may allow better identification of patients with renal impairment.

Early renal failure detection by cystatin C in Type 2 diabetes mellitus: varying patterns of renal analyte expression

AIM

The early stages of renal failure are poorly diagnosed by current routine tests. We studied cystatin C and routine renal analyte patterns in Type 2 diabetes mellitus.

METHODS

Type 2 diabetes mellitus patients (n = 48) were tested for serum cystatin C, urine albumin, haemoglobin A1c, serum creatinine, serum urea, urine creatinine, glucose, triglycerides and low density lipoproteins (LDL). Glomerular filtration rate (GFR) estimates were made using Cockroft-Gault and Modification of Diet in Renal Disease formulae.

RESULTS

The cystatin C (95%CI) reference range was 0.78-0.86 mg/L. While serum cystatin C showed general correlation with routine renal tests, a plateau was observed in analytes measured against cystatin C. Cystatin C improved sensitivity led to detection of renal abnormality in 19% of patients not diagnosed by routine tests.

CONCLUSIONS

Cystatin C is a more sensitive marker of renal disease in Type 2 diabetes mellitus where estimated GFR is unreported at >60 mL/min and where antihypertensive medications render microalbuminuria detection unreliable. Its incorporation into a panel of renal function tests is highly recommended.

Novel biomarkers early predict the severity of acute kidney injury after cardiac surgery in adults

BACKGROUND

The purpose of this study was to investigate the ability of neutrophil gelatinase-associated lipocalin (NGAL), cystatin C, and their combination in predicting the duration and severity of acute kidney injury (AKI) after cardiac surgery in adults.

METHODS

Using data from a prospective observational study of 100 adult cardiac surgical patients, we correlated early postoperative concentrations of plasma NGAL and serum cystatin C with the duration (time during which AKI persisted according to the Acute Kidney Injury Network criteria) and severity of AKI (change in serum creatinine) and with length of stay in intensive care.

RESULTS

We found a mean AKI duration of 67.2 +/- 41.0 hours which was associated with prolonged hospitalization (p < 0.001). NGAL, cystatin C, and their combination on arrival in intensive care correlated with subsequent AKI duration (all p < 0.01) and severity (all p < 0.001). The area under the receiver operating characteristic curve for AKI prediction was 0.77 (95% confidence interval: 0.63 to 0.91) for NGAL and 0.76 (95% confidence interval: 0.61 to 0.91) for cystatin C on arrival in intensive care. Both markers also correlated with length of stay in intensive care (p = 0.037; p = 0.001). Neutrophil gelatinase-associated lipocalin and cystatin C were independent predictors of AKI duration and severity and of length of stay in intensive care (all p < 0.05). The value of cystatin C on arrival in intensive care appeared to be due to a carry-over effect from preoperative values.

CONCLUSIONS

Immediately postoperatively, NGAL and cystatin C correlated with and were independent predictors of duration and severity of AKI and duration of intensive care stay after adult cardiac surgery. The combination of both renal biomarkers did not add predictive value.

Urine neutrophil gelatinase-associated lipocalin moderately predicts acute kidney injury in critically ill adults

Urine neutrophil gelatinase-associated lipocalin (uNGAL) has shown promise as a biomarker for the early detection of acute kidney injury (AKI) in fixed models of injury, but its ability to predict AKI and provide prognostic information in critically ill adults is unknown. We prospectively studied a heterogeneous population of 451 critically ill adults, 64 (14%) and 86 (19%) of whom developed AKI within 24 and 48 h of enrollment, respectively. Median uNGAL at enrollment was higher among patients who developed AKI within 48 h compared with those who did not (190 versus 57 ng/mg creatinine, P < 0.001). The areas under the receiver operating characteristic curves describing the relationship between uNGAL level and the occurrence of AKI within 24 and 48 h were 0.71 (95% Confidence Intervals [CI]: 0.63 to 0.78) and 0.64 (95% CI: 0.57 to 0.71), respectively. Urine neutrophil gelatinase-associated lipocalin remained independently associated with the development of AKI after adjustment for age, serum creatinine closest to enrollment, illness severity, sepsis, and intensive care unit (ICU) location, although it only marginally improved the predictive performance of the clinical model alone. A Cox proportional hazards model using time to first dialysis, adjusted for APACHE II score, suggested that uNGAL independently predicts severe AKI during hospitalization [HR 2.60, 95% CI:1.55 to 4.35]. In summary, although a single measurement of uNGAL exhibited moderate predictive utility for the development and severity of AKI in a heterogeneous ICU population, its additional contribution to conventional clinical risk predictors appears limited.

Contrast-induced nephropathy and long-term adverse events: cause and effect?

BACKGROUND AND OBJECTIVES

The relationship of contrast-induced nephropathy (CIN) to long-term adverse events (AEs) is controversial. Although an association with AEs has been previously reported, it is unclear whether CIN is causally related to these AEs.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We obtained long-term (> or =1 yr) follow-up on 294 patients who participated in a randomized, double-blind comparison of two prevention strategies for CIN (iopamidol versus iodixanol). A difference in the incidence of AEs between patients who had developed CIN and those who had not was performed using a chi(2) test and Poisson regression analysis. A similar statistical approach was used for the differences in AEs between those who received iopamidol or iodixanol. Multiple definitions of CIN were used to strengthen and validate the results and conclusions.

RESULTS

The rate of long-term AEs was higher in individuals with CIN (all definitions of CIN). After adjustment for baseline comorbidities and risk factors, the adjusted incidence rate ratio for AEs was twice as high in those with CIN. Randomization to iopamidol reduced both the incidence of CIN and AEs.

CONCLUSIONS

The parallel decrease in the incidence of CIN and AEs in one arm of this randomized trial supports a causal role for CIN.

Cystatin-C is an independent prognostic factor for survival in multiple myeloma and is reduced by bortezomib administration

BACKGROUND

Renal impairment is a common complication of multiple myeloma. Cystatin-C is considered an accurate marker of glomerular filtration rate in several renal disorders. Microarray analysis has revealed that cystatin-C is one of the most highly up-regulated genes in multiple myeloma. The aim of this study was to evaluate the serum levels of cystatin-C in myeloma patients, explore possible correlations with clinical data, including survival, and assess the effect of bortezomib on cystatin-C in relapsed multiple myeloma.

DESIGN AND METHODS

We measured serum cystatin-C in 157 newly diagnosed, previously untreated myeloma patients, in 28 patients with relapsed disease pre- and post-bortezomib therapy and in 52 healthy controls, using a latex particle-enhanced nephelometric immunoassay.

RESULTS

In newly diagnosed patients, cystatin-C was elevated and showed strong correlations with advanced ISS stage, extensive bone disease, high beta(2)-microglobulin, high serum creatinine, and low creatinine clearance. Multivariate analysis revealed that only cystatin-C and lactate dehydrogenase had an independent prognostic impact on patients' survival. The combination of cystatin-C and lactate dehydrogenase revealed three prognostic groups of patients: a high-risk group (both elevated cystatin-C and lactate dehydrogenase) with a median survival of 24 months, an intermediate-risk group (elevated cystatin-C or elevated lactate dehydrogenase) with a median survival of 48 months and a low-risk group (both low cystatin-C and lactate dehydrogenase) in which median survival has not yet been reached (p<0.001). Cystatin-C could also identify a subset of ISS-II patients with worse outcome. Relapsed patients had higher cystatin-C levels even compared to newly diagnosed patients. Treatment with bortezomib produced a significant reduction of cystatin-C, mainly in responders.

CONCLUSIONS

Serum cystatin-C is not only a sensitive marker of renal impairment but also reflects tumor burden and is of prognostic value in myeloma. Its reduction after treatment with bortezomib reflects bortezomib's anti-myeloma activity and possibly bortezomib's direct effect on renal function.

Acute kidney injury in the intensive care unit

Acute kidney injury (AKI) is common among critically ill patients and results in increased mortality in this population. This review focuses on the diagnosis and management of AKI. The authors first explore new aspects of diagnosis, including new criteria that take into account even modest changes in renal function, and the development of novel biomarkers to allow earlier identification and better differential diagnosis of AKI. The authors also explore the available data on choice of dialysis modality and dialysis dose for the treatment of AKI, as well as the breakthrough development of the bioartificial kidney. Last, the authors review co-interventions that may have relevance to prognosis of AKI, such as intensive insulin therapy and the use of erythropoietin.

Pharmacologic management of the cardiorenal syndrome in heart failure

Cardiorenal syndrome describes the impairment of renal function and associated diuretic resistance in patients with heart failure and clinically manifest volume overload. The pathophysiology of this syndrome is poorly understood, but appears to be caused by impairment of tubuloglomerular feedback, neurohormonal activation, and other factors and therapies used in the management of heart failure. Early diagnosis of the cardiorenal syndrome by way of markers of renal injury and function is critical for timely interventions that may attenuate progression. Many novel therapies have been evaluated in the cardiorenal syndrome setting, including agents that block key local factors (eg, adenosine A(I) receptor antagonists), improve diuresis, aquaresis, and natriuresis, and augment natural vasodilator mechanisms to improve renal perfusion. Furthermore, device-based approaches such as ultrafiltration may also play an important therapeutic role.

Pharmacological optimization of tissue perfusion

After fluid resuscitation, vasoactive drug treatment represents the major cornerstone for correcting any major impairment of the circulation. However, debate still rages as to the choice of agent, dose, timing, targets, and monitoring modalities that should optimally be used to benefit the patient yet, at the same time, minimize harm. This review highlights these areas and some new pharmacological agents that broaden our therapeutic options.

Preventing contrast-induced nephropathy: problems, challenges and future directions

Contrast-induced nephropathy is an injury to the kidney occurring as a result of exposure to intravascular contrast media. It results in both short- and long-term adverse events including mortality. Since treatment of the injury after it has occurred is ineffective, efforts to prevent the injury are the focus of investigators and clinicians alike. In this commentary, the pathogenesis and clinical relevance of contrast-induced nephropathy are reviewed. Prophylactic strategies are discussed with a focus on the use of meta-analysis of small single-center trials.

Novel and conventional serum biomarkers predicting acute kidney injury in adult cardiac surgery--a prospective cohort study

OBJECTIVE

To compare the value of novel with conventional serum biomarkers in the prediction of acute kidney injury (AKI) in adult cardiac surgical patients according to preoperative renal function.

DESIGN

Single-center, prospective observational study.

SETTING

Tertiary hospital.

PATIENTS

One hundred adult cardiac surgical patients.

MEASUREMENTS AND MAIN RESULTS

We measured concentrations of plasma neutrophil gelatinase-associated lipocalin (NGAL), and serum cystatin C, and creatinine and urea at baseline, on arrival in the intensive care unit (ICU) and at 24 hours postoperatively. We assessed such biomarkers in relation to the development of AKI (>50% increase in creatinine from baseline) and to a composite end point (need for renal replacement therapy and in-hospital mortality). We defined an area under the receiver operating characteristic curve of 0.60-0.69 as poor, 0.70-0.79 as fair, 0.80-0.89 as good, and 0.90-1.00 as excellent in terms of predictive value. On arrival in ICU, plasma NGAL and serum cystatin C were of good predictive value, but creatinine and urea were of poor predictive value. After exclusion of patients with preoperative renal impairment (estimated glomerular filtration rate <60 mL/min), the predictive performance for AKI of all renal biomarkers on arrival in ICU remained unchanged except for cystatin C, which was of fair value in such patients. At 24 hours postoperatively, all renal biomarkers were of good predictive value. On arrival in ICU, novel biomarkers were superior to conventional biomarkers (p < 0.05). Plasma NGAL (p = 0.015) and serum cystatin C (p = 0.007) were independent predictors of AKI and of excellent value in the prediction of the composite end point.

CONCLUSIONS

Early postoperative measurement of plasma NGAL was of good value in identifying patients who developed AKI after adult cardiac surgery. Plasma NGAL and serum cystatin C were superior to conventional biomarkers in the prediction of AKI and were also of prognostic value in this setting.

Urinary biomarkers in the early detection of acute kidney injury after cardiac surgery

BACKGROUND AND OBJECTIVES

Serum creatinine (Scr) does not allow for early diagnosis of acute kidney injury (AKI). The diagnostic utility of urinary kidney injury molecule-1 (KIM-1), N-acetyl-beta-D-glucosaminidase (NAG), and neutrophil gelatinase associated lipocalin (NGAL) was evaluated for the early detection of postoperative AKI in a prospective study of 90 adults undergoing cardiac surgery. Designs, setting, participants, & measurements: Urinary KIM-1, NAG, and NGAL were measured at 5 time points for the first 24 h after operation and normalized to the urinary creatinine concentration after cardiac surgery. Receiver-operating characteristic curves were generated and the areas under the curve (AUCs) compared for performance of biomarkers in detection of postoperative AKI.

RESULTS

Thirty-six patients developed AKI, defined as an increase in Scr of > or =0.3 mg/dl within 72 h after surgery. The AUCs for KIM-1 to predict AKI immediately and 3 h after operation were 0.68 and 0.65; 0.61 and 0.63 for NAG; and 0.59 and 0.65 for NGAL, respectively. Combining the three biomarkers enhanced the sensitivity of early detection of postoperative AKI compared with individual biomarkers: the AUCs for the three biomarkers combined were 0.75 and 0.78. The performance of combining biomarkers was even better among 16 early postoperative AKI patients with AUCs of 0.80 and 0.84, respectively.

CONCLUSIONS

The results of this study support that a combination of urinary biomarkers may allow for early detection of postoperative AKI after cardiac surgery before a rise in Scr.

Cystatin C is correlated with mortality in patients with and without acute kidney injury

BACKGROUND

Recent research has shown cystatin C to predict mortality and cardiovascular morbidity independent of renal function. The aim of this study was to evaluate the prognostic value of cystatin C on mortality in adult general ICU patients with acute kidney injury (AKI). We later expanded the study and included patients without signs of AKI.

METHODS

A total of 845 ICU patients were analysed for cystatin C and classified according to the RIFLE criteria. Of these, 271 patients with either creatinine >150 micromol/l, urea >25 or anuria/oliguria entered the AKI cohort. The remaining 562 patients entered the non-AKI cohort. Both cohorts were divided into quartiles according to cystatin C at entry. In the non-AKI cohort, we split the highest cystatin C quartile into two. The relationship between the different cystatin C quartiles and mortality in patients with and without AKI was estimated by hazard ratios (HR) derived from the Cox proportional hazards regression model.

RESULTS

A relationship between cystatin C and mortality was found in patients with and without AKI, being stronger in patients without AKI. In AKI patients, the HR comparing cystatin C above and below the median more than doubled from the second year on compared to the first year follow-up. After exclusion of patients in the non-AKI cohort with 'potential AKI' (creatinine >100 micromol/l or urea > 20 mmol/l), the correlation between cystatin C levels and risk of death was strengthened.

CONCLUSIONS

Cystatin C is correlated with mortality independently of renal function measured by creatinine in patients entering the general ICU.