Early detection of acute renal failure by serum cystatin C

New biomarkers for acute renal injury

Incidence of acute kidney injury (AKI) is increasing rapidly to epidemic proportions. Development of AKI, especially in intensive care settings, is associated with increased morbidity, mortality and hospitalization costs. Currently available diagnostic tools are mostly insensitive for early diagnosis, however prompt diagnosis and risk stratification are necessary for guiding therapy and preventing progression of disease. Finding an early, reliable, suitable, easily reproducible, economical and accurate biomarker for AKI is a top research priority. In recent years, many urinary and serum proteins have been investigated as possible early markers of AKI and some of them have shown great promise. This topic reviews some of the emerging biomarkers of AKI.

Molecular markers of kidney injury

Renal dysfunction is common in urologic patients, especially in those undergoing nephrectomy for renal cancer. Partial nephrectomy better preserves renal function than radical nephrectomy, but is associated with acute kidney injury related to loss of nephrons and ischemic injury. Ischemic injury may not be reliably assessed using common clinical parameters, such as serum creatinine and urine output, which may delay detection of clinically-significant kidney damage. Molecular markers, such as cystatin C, neutrophil gelatinase-associated lipocalin (NGAL), IL-18 and kidney injury molecule-1 (KIM-1), better quantify the extent of acute ischemic and/or tubular injury than other currently available tools. The use of these and/or other markers may facilitate research to improve outcomes following partial nephrectomy.

Impact of N-acetylcysteine on contrast-induced nephropathy defined by cystatin C in patients with ST-elevation myocardial infarction undergoing primary angioplasty

BACKGROUND

The aim of this study was to assess the effects of N-acetylcysteine (N-ACC) on contrast-induced nephropathy (CIN) defined by Cystatin C (Cys-C) serum levels and to evaluate the influence of Cys-C on clinical outcome in patients with ST-elevation myocardial infarction (STEMI).

METHODS

In total, 251 patients with STEMI undergoing primary percutaneous coronary intervention (PCI) were randomized to either high-dose N-ACC (2 × 1200 mg/d for 48 h) with optimal hydration or placebo plus optimal hydration. Serum Cys-C was measured at baseline, immediately, 24, 48 and 72 h after PCI. CIN was defined as an increase in serum Cys-C levels of 25% or more from baseline within 72 h after PCI. Major adverse cardiac events (MACE)--defined as death, recurrent infarction and congestive heart failure--within 6 months were recorded.

RESULTS

Baseline Cys-C was 1294 ± 611 and 1352 ± 811 ng/mL (p = 0.54) for the N-ACC and placebo group, respectively. There was a steady increase in Cys-C in both groups within the first 72 h after randomization. CIN occurred in 74.6 and in 70.4% of patients in the N-ACC and placebo group, respectively (p = 0.46). The magnitude of increase in the serum concentration of Cys-C was an independent predictor for MACE after 6 months of follow-up.

CONCLUSIONS

High-dose N-ACC does not provide additional benefit over placebo with respect to Cys-C defined CIN in STEMI patients undergoing primary PCI. The magnitude of increase in Cys-C serum levels in the early course after STEMI is a predictor of medium-term MACE.

Lung-protective mechanical ventilation does not protect against acute kidney injury in patients without lung injury at onset of mechanical ventilation

INTRODUCTION

Preclinical and clinical studies suggest that mechanical ventilation contributes to the development of acute kidney injury (AKI), particularly in the setting of lung-injurious ventilator strategies.

OBJECTIVE

To determine whether ventilator settings in critically ill patients without acute lung injury (ALI) at onset of mechanical ventilation affect the development of AKI.

DESIGN, SETTING, AND PATIENTS

Secondary analysis of a randomized controlled trial (N = 150), comparing conventional tidal volume (V(T), 10 mL/kg) with low tidal volume (V(T), 6 mL/kg) mechanical ventilation in critically ill patients without ALI at randomization. During the first 5 days of mechanical ventilation, the RIFLE class was determined daily, whereas neutrophil gelatinase-associated lipocalin and cystatin C levels were measured in plasma collected on days 0, 2, and 4.

RESULTS

Eighty-six patients had no AKI at inclusion, and 18 patients (21%) subsequently developed AKI, but without significant difference between ventilation strategies. (Cumulative hazard, 0.26 vs 0.23; P = .88.) The courses of neutrophil gelatinase-associated lipocalin and cystatin C plasma levels did not differ significantly between randomization groups.

CONCLUSION

In the present study in critically patients without ALI at onset of mechanical ventilation, lower tidal volume ventilation did not reduce the development or worsening of AKI compared with conventional tidal volume ventilation.

Cystatin C in diabetics as a marker of mild renal insufficiency after CABG

PURPOSE

The purpose of this study was to evaluate the accuracy of plasma cystatin C in acute impairment in renal function; plasma cystatin C was compared to plasma creatinine in two hundred patients undergoing elective CABG surgery.

METHODS

We performed a prospective clinical study of two hundred patients undergoing coronary bypass surgery. Plasma creatinine and cystatin C were measured preoperatively and on the first and fourth days after surgery. Estimated glomerular filtration rate (GFR) was calculated using one creatinine-based and two cystatin C-based equations.

RESULTS

There were 144 non-diabetic and 56 diabetic patients. The need for furosemide was more common among diabetics (80.4% of the patients vs. 53.9%, p = 0.024). Changes in cystatin C-based GFR with both equations were significantly greater in the group of diabetics (-14.3 ± 28.0 and -11.2 ± 19.3 ml/min/1.73 m(2) vs. -4.3 ± 26.9 and -3.1 ± 20.5 ml/min/1.73 m(2), p = 0.025 and 0.016, respectively). Changes in creatinine-based GFR did not differ between the diabetics and the non-diabetics.

CONCLUSION

Cystatin C and cystatin C-based estimation of GFR may be useful and more sensitive than creatinine in detecting mild acute renal insufficiency in diabetic patients.

Diagnostic value of cystatin C for predicting acute kidney injury in patients with liver cirrhosis

BACKGROUND/AIMS

The present study aimed to determine the role of cystatin C as a prognostic factor for acute kidney injury and survival in cirrhotic patients.

METHODS

The study investigated 53 liver cirrhosis patients. The renal function was evaluated by serum creatinine, serum and urine cystatin C, and 24-hour creatinine clearance on admission. Acute kidney injury was defined as a serum creatinine level exceeding the normal range (>1.2 mg/dl) and an increase of at least 50% from the baseline value. Multivariate analysis, receiver operating characteristic curve, and survival analysis were used to investigate prognostic factors for acute kidney injury and survival.

RESULTS

Nine of the 53 cirrhotic patients (17.0%) developed acute kidney injury within 3 months. Both serum creatinine and cystatin C were predictive factors for acute kidney injury in univariate analysis, with a diagnostic accuracy of 0.735 (95% confidence interval (CI), 0.525-0.945; p=0.028) for serum cystatin C and 0.698 (95% CI, 0.495-0.901, p=0.063) for creatinine. In multivariate analysis, only serum cystatin C was an independent risk factor for acute kidney injury. The sensitivity and specificity of a serum cystatin C level of >1.23 mg/L to acute kidney injury were 66% and 86%, respectively. Serum cystatin C was positively correlated with the Model for End-Stage Liver Disease (MELD) and MELD-Na scores (r=0.346 and p=0.011, and r=0.427 and p=0.001, respectively). Comparison of the survival rates over the observation period revealed that a serum cystatin C level of >1.23 mg/L was a useful marker for short-term mortality (p<0.001).

CONCLUSIONS

The accuracy in predicting acute kidney injury and short-term mortality was higher for a serum cystatin C level of >1.23 mg/L than for the serum creatinine concentration in patients with cirrhosis.

Effect of captopril treatment on recuperation from ischemia/reperfusion-induced acute renal injury

BACKGROUND

Ischemia/reperfusion triggers acute kidney injury (AKI), mainly via aggravating hypoxia, oxidative stress, inflammation and renin-angiotensin system (RAS) activation. We investigated the role of angiotensin-converting enzyme (ACE) inhibition on the progression of AKI in a rat model of ischemia/reperfusion.

METHODS

Ninety-nine Sprague-Dawley rats were subjected to 1 h ischemia/reperfusion and/or left unilateral nephrectomy, with concurrent intraperitoneal implantation of Alzet pump. Via this pump, they were continuously infused with captopril 0.5 mg/kg/day, captopril 2 mg/kg/day or saline. The rats were sacrificed following 24, 48 or 168 h. Blood samples, 24-h urine collections and kidneys were allocated, to evaluate renal function, angiotensin-II, nitric oxide (NO), apoptosis, hypoxia, oxidative stress and inflammation.

RESULTS

Serum creatinine and cystatin-C significantly increased in ischemic rats, coinciding with histopathologic intrarenal damage, decreased NO, augmented angiotensin-II, interleukin (IL)-6, IL-10, transforming growth factor-beta. At the acute reperfusion stage, captopril prevented excessive angiotensin-II synthesis, ameliorated renal dysfunction, inhibited intrarenal inflammation and improved histopathologic findings. Most of the renoprotective effects of captopril were limited predominantly to acute reperfusion stage. Concurrently, captopril significantly decreased NO availability, exacerbated intrarenal hypoxia and augmented oxidative stress.

CONCLUSIONS

At the acute stage of renal ischemia/reperfusion-induced AKI, ACE inhibition substantially contributed to the amelioration of acute injury by improving renal function, inhibiting systemic and intrarenal angiotensin-II, attenuating intrarenal inflammation and preserving renal tissue structure. Later on, at the post-reperfusion stage, most of the beneficial effects of captopril administration on the recuperating post-ischemic kidney were no longer evident. Concurrently, ACE inhibition exacerbated intrarenal hypoxia and accelerated oxidative stress, indicating that renal adaptation to some consequences of ischemia does require bioavailability of RAS components.

Urine proteomics in kidney and urogenital diseases: Moving towards clinical applications

To date, multiple biomarker discovery studies in urine have been conducted. Nevertheless, the rate of progression of these biomarkers to qualification and even more clinical application is extremely low. The scope of this article is to provide an overview of main clinically relevant proteomic findings from urine focusing on kidney diseases, bladder and prostate cancers. In addition, approaches for promoting the use of urine in clinical proteomics including potential means to facilitate the validation of existing promising findings (biomarker candidates identified from previous studies) and to increase the chances for success for the identification of new biomarkers are discussed.

A comparison of alternative serum biomarkers with creatinine for predicting allograft function after kidney transplantation

BACKGROUND

The role of serum cystatin C (Scyc), neutrophil gelatinase-associated lipocalin, and interleukin-18 in predicting early graft function after kidney transplant is poorly defined.

METHODS

We conducted a multicenter prospective cohort study of deceased-donor kidney transplants. We collected serial blood samples for the first 3 days of transplant and monitored need for dialysis within 1 week and graft function at 3 months after transplant.

RESULTS

Among 78 recipients with serum biomarker measurements, 26 had delayed graft function (DGF; hemodialysis within 1 week of transplant). Of those not dialyzed, 29 had slow graft function (serum creatinine [Scr] reduction from transplantation to day 7 <70%), and 23 had immediate graft function (IGF; reduction in Scr ≥70%). Scyc levels were statistically different between groups by the first postoperative day (POD), whereas Scr levels were not. Serum neutrophil gelatinase-associated lipocalin and serum interleukin-18 levels were not different between groups. Scyc on the first POD demonstrated good utility for predicting DGF and non-IGF (DGF or slow graft function) with areas under the receiver-operating characteristic curve of 0.83 and 0.85, respectively. Areas under the receiver-operating characteristic curve for predicting DGF and non-IGF using Scr on the first POD were 0.65 and 0.53, respectively. Substituting Scyc for Scr in a clinical algorithm improved its utility for predicting DGF or non-IGF, with adjusted odds ratios of 2.4 and 3.3 for Scyc levels on the first POD. The change in Scyc during the first POD demonstrated a dose-response relationship with 3-month graft function.

CONCLUSIONS

Scyc outperforms Scr as a predictor of early graft function after deceased-donor kidney transplant.

The outcome of neutrophil gelatinase-associated lipocalin-positive subclinical acute kidney injury: a multicenter pooled analysis of prospective studies

OBJECTIVES

The aim of this study was to test the hypothesis that, without diagnostic changes in serum creatinine, increased neutrophil gelatinase-associated lipocalin (NGAL) levels identify patients with subclinical acute kidney injury (AKI) and therefore worse prognosis.

BACKGROUND

Neutrophil gelatinase-associated lipocalin detects subclinical AKI hours to days before increases in serum creatinine indicate manifest loss of renal function.

METHODS

We analyzed pooled data from 2,322 critically ill patients with predominantly cardiorenal syndrome from 10 prospective observational studies of NGAL. We used the terms NGAL(-) or NGAL(+) according to study-specific NGAL cutoff for optimal AKI prediction and the terms sCREA(-) or sCREA(+) according to consensus diagnostic increases in serum creatinine defining AKI. A priori-defined outcomes included need for renal replacement therapy (primary endpoint), hospital mortality, their combination, and duration of stay in intensive care and in-hospital.

RESULTS

Of study patients, 1,296 (55.8%) were NGAL(-)/sCREA(-), 445 (19.2%) were NGAL(+)/sCREA(-), 107 (4.6%) were NGAL(-)/sCREA(+), and 474 (20.4%) were NGAL(+)/sCREA(+). According to the 4 study groups, there was a stepwise increase in subsequent renal replacement therapy initiation-NGAL(-)/sCREA(-): 0.0015% versus NGAL(+)/sCREA(-): 2.5% (odds ratio: 16.4, 95% confidence interval: 3.6 to 76.9, p < 0.001), NGAL(-)/sCREA(+): 7.5%, and NGAL(+)/sCREA(+): 8.0%, respectively, hospital mortality (4.8%, 12.4%, 8.4%, 14.7%, respectively) and their combination (4-group comparisons: all p < 0.001). There was a similar and consistent progressive increase in median number of intensive care and in-hospital days with increasing biomarker positivity: NGAL(-)/sCREA(-): 4.2 and 8.8 days; NGAL(+)/sCREA(-): 7.1 and 17.0 days; NGAL(-)/sCREA(+): 6.5 and 17.8 days; NGAL(+)/sCREA(+): 9.0 and 21.9 days; 4-group comparisons: p = 0.003 and p = 0.040, respectively. Urine and plasma NGAL indicated a similar outcome pattern.

CONCLUSIONS

In the absence of diagnostic increases in serum creatinine, NGAL detects patients with likely subclinical AKI who have an increased risk of adverse outcomes. The concept and definition of AKI might need re-assessment.

Acute kidney insufficiency in the critically ill

Acute kidney insufficiency (AKI), or injury, is common in the critically ill patient. Minimal increases in serum creatinine (Scr) have been associated with greater morbidity, mortality, and hospital cost. In 2002, the Acute Dialysis Quality Initiative (ADQI) proposed a consensus definition (the RIFLE classification) which was modified after continuing evidence suggested that small changes in Scr (≥0.3 mg/dL) led to worsening outcomes. This group, known as the Acute Kidney Injury Network (AKIN), suggests 3 stages of worsening kidney function. Such definitions may aid in identifying patients at greatest risk and further the development of preventive strategies. This review will focus on the epidemiology and etiology of AKI as well as provide a mechanistic description of drug-induced AKI. In addition, a brief review of continuous renal replacement therapies is provided.

Urine cystatin C as a biomarker of proximal tubular function immediately after kidney transplantation

BACKGROUND/AIMS

Clinical methods to predict allograft function soon after kidney transplantation are ineffective.

METHODS

We analyzed urine cystatin C (CyC) in a prospective multicenter observational cohort study of deceased-donor kidney transplants to determine its peritransplant excretion pattern, utility for predicting delayed graft function (DGF) and association with 3-month graft function. Serial urine samples were collected for 2 days following transplant and analyzed blindly for CyC. We defined DGF as any hemodialysis in the first week after transplant, slow graft function (SGF) as a serum creatinine reduction < 70% by the first week and immediate graft function (IGF) as a reduction ≥ 70%.

RESULTS

Of 91 recipients, 33 had DGF, 34 had SGF and 24 had IGF. Urine CyC/urine creatinine was highest in DGF for all time-points. The area under the curve (95% CI) for predicting DGF at 6 h was 0.69 (0.57-0.81) for urine CyC, 0.74 (0.62-0.86) for urine CyC/urine creatinine and 0.60 (0.45-0.75) for percent change in urine CyC. On the first postoperative day, urine CyC/urine creatinine and percent change in urine CyC were associated with 3-month graft function.

CONCLUSION

Urine CyC on the day after transplant differs between degrees of perioperative graft function and modestly corresponds with 3-month function.

Biological markers of acute kidney injury

An abrupt change in serum creatinine, the most common indicator of acute kidney injury (AKI), is strongly linked to poor outcomes across multiple clinical settings. Despite endless attempts to distill the magnitude and timing of a changing serum creatinine into a standardized metric, singular focus on this traditional functional marker obligates the characterization of AKI to remain, at best, retrospective and causally noninformative. The resultant inability to meaningfully segregate critical aspects of injury such as type, onset, propagation, and recovery from ongoing decrements in renal function has hindered successful translation of promising therapeutics. Over the past decade, however, the emerging field of clinical proteomics reinvigorates hope of identifying novel plasma and urine biomarkers to characterize cause and course of kidney injury. Efforts to validate these markers for use in clinical studies now show early promise but face important obstacles including interpretive difficulties inherent in using serum creatinine as a sole comparator for diagnostic performance, a need to better evaluate the incremental performance of new markers above established clinical and biochemical predictors, a relative lack of power to sufficiently examine hard clinical end points, and a potential over-reliance on use alone of receiver operating curves for assessing biomarker utility. Here, we discuss efforts to address these barriers and further ascertain the clinical value of new markers.

Emergence of biomarkers in nephropharmacology

Blood-urea nitrogen, serum creatinine and urine output have long been used as markers of kidney function despite their known limitations. In the past few years, a number of novel biomarkers have been identified in the urine and blood that can detect kidney injury early. Although, to date, none of these biomarkers are in clinical use, many have been validated as reliable and sensitive, allowing detection of kidney injury before serum creatinine levels rise and urine output drops. These markers have been evaluated in great detail in animal models and to a lesser extent in humans in postcardiopulmonary bypass and sepsis. There is relatively scarse data on the use of these biomarkers in the detection of kidney injury associated with the use of pharmacologic agents. The purpose of this article is to summarize these data and highlight the potential utility of these biomarkers in nephropharmacology.

Urinary biomarkers in prenatally diagnosed unilateral hydronephrosis

The introduction of prenatal ultrasonography as a screening method entails an increasing number of infants diagnosed with prenatal hydronephrosis. Ureteropelvic junction obstruction accounts for 35% of prenatal hydronephrotic cases. Urinary tract obstruction that occurs during early kidney development affects renal morphogenesis, maturation and growth, and in the most severe cases this will ultimately cause renal insufficiency. A major challenge in the clinical management of these patients is to preserve renal function by selection of the 15%-20% who require early surgical intervention, leaving those for whom watchful waiting may be appropriate because of spontaneous resolution/stabilization without significant loss of renal function. Today, this requires medical surveillance, including repetitive invasive diuretic renograms relying on arbitrary threshold values, and therefore there is a need for non-arbitrary, non-invasive urinary biomarkers that may be used as predictors for renal structural changes and/or decreasing renal function, and thereby provide the surgeon with more clear indications for surgical intervention. In this review, we summarize the currently well-known facts about urinary biomarkers in ureteropelvic junction obstruction concerning renal function, and we also suggest potential novel urinary biomarkers.

Subtle change of cystatin C, with or without acute kidney injury, associated with increased mortality in the intensive care unit

PURPOSE

Recent epidemiologic studies suggest a significant association between small increases in serum creatinine (sCr) and adverse outcomes. The Acute Kidney Injury Network (AKIN) sought to increase the sensitivity of the AKIN criteria for acute kidney injury (AKI) by recommending the use of small changes in sCr for the diagnosis of AKI. Several recent studies have reported that serum cystatin C (cysC) is more accurate than sCr as a surrogate for the glomerular filtration rate. This study was performed to determine whether small increases in cysC (≥0.3 mg/L within 48 hours) are associated with clinical outcomes in critically ill patients.

MATERIALS AND METHODS

This was a prospective study of 274 consecutive patients admitted to the intensive care unit. Clinical data, including urine output, sCr, cysC, and outcomes, were collected for up to 3 months. Kaplan-Meier curves were used to determine the 90-day survival rate. Mortality was adjusted according to the Cox proportional hazards model.

RESULTS

Acute kidney injury developed in 84 (30.7%) patients based on the AKIN criteria. Among these patients, 42 (50%) had stage 1; 8 (9.5%), stage 2; and 34 (40.4%), stage 3 disease. Fourteen patients with increased cysC did not have AKI by AKIN criteria. The overall 90-day mortality was 20.8%. When mortality was stratified by group, it was 5.7% for the no-AKI-without-cysC-increment group, 28.6% for the no-AKI-with-increased-cysC group, 33.3% for the AKIN stage 1 group, 62.5% for the AKIN stage 2 group, and 70.6% for the AKIN stage 3 group (P < .001). Kaplan-Meier curves were constructed for each group based on stage and 90-day survival. The Cox analysis showed that patients who met AKIN criteria and patients with increases of cysC without AKI had associated mortality. In addition, patients with increases in cysC without AKI had outcomes similar to the patients with stage 1 AKI.

CONCLUSIONS

Small increases of cysC were associated with increased mortality in intensive care unit patients independent of diagnosis of AKI by AKIN criteria.

Classification and staging of acute kidney injury: beyond the RIFLE and AKIN criteria

Acute kidney injury (AKI) is often overlooked in hospitalized patients, despite the fact that even mild forms are strongly associated with poor clinical outcomes such as increased mortality, morbidity, cardiovascular failure and infections. Research endorsed by the Acute Dialysis Quality Initiative led to the publication of a consensus definition for AKI--the RIFLE criteria (Risk, Injury, Failure, Loss of function, and End-stage renal disease)--which was designed to standardize and classify renal dysfunction. These criteria, along with revised versions developed by the AKI Network (AKIN), can detect AKI with high sensitivity and high specificity and describe different severity levels that aim to predict the prognosis of affected patients. The RIFLE and AKIN criteria are easy to use in a variety of clinical and research settings, but have several limitations: both utilize an increase in serum creatinine level from a hypothetical baseline value and a decrease in urine output, but these surrogate markers of renal impairment manifest relatively late after injury has occurred and do not consider the nature or site of the kidney injury. New biomarkers for AKI have shown promise for early diagnosis and prediction of the prognosis of AKI. As more data become available, they could, in the future, be incorporated into improved definitions or criteria for AKI.

Neutrophil gelatinase-associated lipocalin in the diagnosis of type 1 cardio-renal syndrome in the general ward

BACKGROUND AND OBJECTIVES

The early identification of acute heart failure (HF) patients with type 1 cardio-renal syndrome should be the first step for developing prevention and treatment strategies for these patients. This study aimed to assess the performance of neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C in the early detection of type 1 cardio-renal syndrome in patients with acute HF.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

One-hundred nineteen patients admitted with acute HF were studied. NGAL and creatinine were measured in the first hospitalization morning; creatinine was also measured at least after 48 to 72 hours. Physicians were blinded to NGAL and cystatin C levels. Type 1 cardio-renal syndrome was defined as an increase in the creatinine level of at least 0.3 mg/dl or 50% of basal creatinine.

RESULTS

Type 1 cardio-renal syndrome developed within 48 to 72 hours in 14 patients (11.8%). Admission NGAL levels were higher in these patients: 212 versus 83 ng/dl. At a cutoff value of 170 ng/L, NGAL determined type 1 cardio-renal syndrome with a sensitivity of 100% and a specificity of 86.7%. The area under the receiver-operating characteristic curve of NGAL was 0.93 and that of cystatin C was 0.68.

CONCLUSIONS

Above a cutoff value of 170 ng/L, NGAL predicts 48- to 72-hour development of type 1 cardio-renal syndrome with a negative predictive value of 100% and a positive predictive value of 50%. NGAL independently associates with type 1 cardio-renal syndrome and might be a useful biomarker in the early recognition of these patients.

Significant differences when using creatinine, modification of diet in renal disease, or cystatin C for estimating glomerular filtration rate in ICU patients

BACKGROUND

Renal dysfunction is associated with increased morbidity and mortality in intensive care patients. In most cases the glomerular filtration rate (GFR) is estimated based on serum creatinine and the Modification of Diet in Renal Disease (MDRD) formula, but cystatin C-estimated GFR is being used increasingly. The aim of this study was to compare creatinine and MDRD and cystatin C-estimated GFR in intensive care patients.

METHODS

Retrospective observational study was performed, on patients treated within the general intensive care unit (ICU) during 2004-2006, in a Swedish university hospital.

RESULTS

GFR markers are frequently ordered in the ICU; 92% of the patient test results had cystatin C-estimated GFR (eGFR(cystatinC)) ≤ 80 mL/min/1.73 m(2), 75% had eGFR ≤ 50 mL/min/1.73 m(2), and 30% had eGFR ≤ 20 mL/min/1.73 m(2). In contrast, only 46% of the patients had reduced renal function assessed by plasma creatinine alone, and only 47% had eGFR(MDRD) ≤ 80 mL/min/1.73 m(2). The mean difference between eGFR(MDRD) and eGFR(cystatinC) was 39 mL/min/1.73 m(2) for eGFR(cystatinC) values ≤ 60 mL/min/1.73 m(2).

CONCLUSIONS

GFR is commonly assessed in the ICU. Cystatin C-estimated GFR yields markedly lower GFR results than plasma creatinine and eGFR(MDRD). Many pharmaceuticals are eliminated by the kidney, and their dosage is adjusted for kidney function. Thus, the differences in GFR estimates by the methods used indicate that the GFR method used in the intensive care unit may influence the treatment.

Cardiorenal syndrome and heart failure

PURPOSE OF REVIEW

Concomitant anemia, heart failure, and renal disease can be seen in a large proportion of patients with heart failure. The purpose of this review is to discuss the current definitions and mechanisms involved in this pathophysiological relationship, as well as the potential management and treatment options available for these patients.

RECENT FINDING

Dysfunctional heart can promote the dysfunction of the kidneys through a variety of pathophysiological mechanism, the reciprocal holds true as well. Heart failure has been considered as the most common type of cardiovascular complication seen in patients with renal failure. Central to this relationship lies anemia, which can be the result or the cause of either heart or kidney disease.

SUMMARY

Cardiorenal syndrome is a complex condition, which requires the collaboration and resources from cardiology, cardiac surgery, nephrology, and critical care. Of great importance is recognizing the presence of cardiorenal syndrome and appreciating the impact it can play on treatment options and survival.

Review: Serum and urine biomarkers of kidney disease: A pathophysiological perspective

The use of reliable biomarkers is becoming increasingly important for the improved management of patients with acute and chronic kidney diseases. Recent developments have identified a number of novel biomarkers in serum or urine that can determine the potential risk of kidney damage, distinguish different types of renal injury, predict the progression of disease and have the potential to assess the efficacy of therapeutic intervention. Some of these biomarkers can be used independently while others are more beneficial when used in combination with knowledge of other clinical risk factors. Advances in gene expression analysis, chromatography, mass spectrometry and the development of sensitive enzyme-linked immunosorbent assays have facilitated accurate quantification of many biomarkers. This review primarily focuses on describing new and established biomarkers, which identify and measure the various pathophysiological processes that promote kidney disease. It provides an overview of some of the different classes of renal biomarkers that can be assessed in serum/plasma and urine, including markers of renal function, oxidative stress, structural and cellular injury, immune responses and fibrosis. However, it does not explore the current status of these biomarkers in terms of their clinical validation.

Acute kidney injury: novel biomarkers and potential utility for patient care in urology

Urologists are integrally involved in the management of acute kidney injury (AKI), which is common after renal surgery or secondary to postrenal (obstructive) etiologies. The measurement of serum creatinine is a suboptimal indicator of AKI because it lags behind acute changes in renal function. Recent advances indicate that serum/urine biomarkers will prove useful for early detection of AKI, analogous to the use of cardiac enzymes for acute myocardial infarction. These serum/urine markers may guide future therapy, facilitate research efforts to reduce the severity of AKI, such as after partial nephrectomy, and allow for more accurate prognostication for patients with AKI.

Evolving use of biomarkers for kidney injury in acute care settings

PURPOSE OF REVIEW

Acute kidney injury is increasingly recognized in acute care settings in more recent years. Proper diagnosis and risk stratification for acute kidney injury is necessary for carrying out appropriate and cost-effective treatments in patients with acute kidney injury. Kidney markers serve as diagnostic and prognostic tools to give physicians a more complete perspective of renal insult. The aim of this review is to highlight some of the evidence from recent studies, involving kidney markers and provide current opinion on the accuracy of these markers.

RECENT FINDINGS

Recent studies demonstrate that novel kidney markers such as cystatin C, interleukin-18, kidney injury molecule 1, and neutrophil gelatinase-associated lipocalin serve as more accurate markers for acute kidney injury as compared with the more traditional marker, creatinine. Additionally, there seems to be a correlation between the concentrations of each marker and the level of deterioration of kidneys, patient recovery time, length of hospital stay, and hospital costs.

SUMMARY

Each individual kidney marker possesses its own strengths and weaknesses in determining the onset and severity of acute kidney injury. However, in combination, a panel of kidney markers may serve as powerful tools in diagnosing kidney injury with high accuracy.

Cardiorenal Syndrome: The Clinical Cardiologists' Perspective

The term cardiorenal syndrome has evolved over the years. The understanding of the interactions between these two organ systems has led to better recognition and treatment strategies. As cardiovascular mortality is high in individuals with renal dysfunction, it is imperative to understand the pathophysiology behind the disease process. This knowledge may better serve these patients with this syndrome and improve their outcomes. In this review, we examine the key issues of the cardiorenal syndrome from a cardiologist's perspective.

Biomarkers of acute kidney injury in children: discovery, evaluation, and clinical application

Acute kidney injury (AKI) in children is associated with increased mortality and prolonged length of hospital stay and may also be associated with long-term chronic kidney disease development. Despite encouraging results on AKI treatment in animal studies, no specific treatment has yet been successful in humans. One of the important factors contributing to this problem is the lack of an early AKI diagnostic test. Serum creatinine, the current main diagnostic test for AKI, rises late in AKI pathophysiology and is an inaccurate marker of acute changes in glomerular filtration rate. Therefore, new biomarkers of AKI are needed. With great advancements in genomics, proteomics, and metabolomics, new AKI biomarkers, mainly consisting of urinary proteins that appear in response to renal tubular cell injury, have been, and continue to be, discovered. These new biomarkers offer promise for early AKI diagnosis and for the depiction of severity of renal injury occurring with AKI. This review provides a summary of what a biomarker is, why we need new biomarkers of AKI, and how biomarkers are discovered and should be evaluated. The review also provides a summary of selected AKI biomarkers that have been studied in children.

The cardiorenal syndrome: a review

Cardiorenal syndrome (CRS) is the umbrella term used to describe clinical conditions in which cardiac and renal dysfunctions coexist. Much has been written on this subject, but underlying pathophysiological mechanisms continue to be unravelled and implications for management continue to be debated. A classification system—incorporating five subtypes—has recently been proposed though it has yet to permeate into day-to-day clinical practice. CRS has garnered much attention from both the cardiological and nephrological communities since the condition is associated with significant morbidity and mortality. Renal dysfunction is highly prevalent amongst patients with heart failure and has been shown to be as powerful and independent a marker of adverse prognosis as ejection fraction. Similarly, patients with renal failure are considerably more likely to suffer cardiovascular disease than matched subjects from the general population. This paper begins by reviewing the epidemiology and classification of CRS before going on to consider the different pathological mechanisms underlying cardiorenal dysfunction. We then focus on management strategies and conclude by discussing future directions in the diagnosis and management of patients suffering with CRS.

[Acute kidney injury: from concept to practice]

Definition and classification of acute renal failure evolved in recent years. The acronym "Acute Kidney Injury" replaces "Acute Renal Failure". The RIFLE classification spreads the AKI in three degrees of severity, and two degrees of disease duration. The group Acute Kidney Injury Network refines this classification into three stages, to improve the sensitivity in detecting moderate forms. The epidemiology of AKI remains imprecise. In the ICU, more than 30% of patients suffered from AKI, often in a context of multiple organs failure. In addition to serum creatinine and urine output, new biomarkers can be assessed. Their early detection should enable a clearer distinction between "acute tubular necrosis" and other causes of AKI, but also to distinguish patients at risk for pejorative evolution of renal function. The management of AKI based on an optimal resuscitation. The administration of loop diuretics or low dose dopamine showed no benefit. Hydration in prevention of the contrast-induced nephropathy is confirmed. The role of acetylcysteine must be determined. The ideal time to initiate a renal replacement therapy and the choice of the technique remain unresolved. The same goes for the dose of dialysis administered. A systematic application of an algorithm, such as proposed by Bagshow would make comparisons easier and the realisation of multicenter studies will help to clarify these points.

Serum and urine cystatin C are poor biomarkers for acute kidney injury and renal replacement therapy

Purpose

To evaluate whether cystatin C in serum (sCyC) and urine (uCyC) can predict early acute kidney injury (AKI) in a mixed heterogeneous intensive care unit (ICU), and also whether these biomarkers can predict the need for renal replacement therapy (RRT).

Methods

Multicenter prospective observational cohort study in patients ≥18 years old and with expected ICU stay ≥72 h. The RIFLE class for AKI was calculated daily, while sCyC and uCyC were determined on days 0, 1, and alternate days until ICU discharge. Test characteristics were calculated to assess the diagnostic performance of CyC.

Results

One hundred fifty-one patients were studied, and three groups were defined: group 0 (N = 60), non-AKI; group 1 (N = 35), AKI after admission; and group 2 (N = 56), AKI at admission. We compared the two days prior to developing AKI from group 1 with the first two study days from group 0. On Day –2, median sCyC was significantly higher (0.93 versus 0.80 mg/L, P = 0.01), but not on Day –1 (0.98 versus 0.86 mg/L, P = 0.08). The diagnostic performance for sCyC was fair on Day –2 [area under the curve (AUC) 0.72] and poor on Day –1 (AUC 0.62). Urinary CyC had no diagnostic value on either of the two days prior to AKI (AUC <0.50). RRT was started in 14 patients with AKI; sCyC and uCyC determined on Day 0 were poor predictors for the need for RRT (AUC ≤0.66).

Conclusions

In this study, sCyC and uCyC were poor biomarkers for prediction of AKI and the need for RRT.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-010-2087-y) contains supplementary material, which is available to authorized users.

Proteomic analysis of acute kidney injury: biomarkers to mechanisms

Acute kidney injury (AKI) is a devastating clinical condition, both in terms of mortality and costs, and is occurring with increasing incidence. Despite better clinical care, the outcomes of AKI have changed little in the last 50 years. This lack of progress is due in part to a lack of early diagnostic biomarkers and a poor understanding of the disease mechanisms. This review will focus on the rapid progress being made in both the understanding of AKI and the promising panel of early biomarkers for AKI that have come out of both direct proteomic analysis of body fluids of AKI patients and more targeted proteomic approaches using clues from other methods such as transcriptomics. This review concludes with a discussion of the future of proteomics and personalized medicine in AKI and the challenges presented in translating these exciting proteomic results to the clinic.

Ability of cystatin C to detect acute changes in glomerular filtration rate provoked by hyperglycaemia in uncomplicated Type 1 diabetes

AIMS

Systematic study of hyperfiltration in diabetic nephropathy has been hindered by the lack of a simple glomerular filtration rate (GFR) measure that is accurate in this range of renal function. Serum cystatin C (GFR(CYSTATIN C) ) reflects long-term trends in GFR in normal or elevated ranges. To test whether it can reflect acute changes, we examined the impact of clamped hyperglycaemia on GFR(CYSTATIN C) and GFR(INULIN) in subjects with Type 1 diabetes.

METHODS

GFR(INULIN) and GFR(CYSTATIN C) were measured in 32 normotensive, normoalbuminuric subjects during clamped euglycaemia and hyperglycaemia. For comparison, GFR(MDRD) was estimated according to the four-variable equation.

RESULTS

During clamped euglycaemia, agreement between GFR(CYSTATIN C) and GFR(INULIN) was excellent, with mean bias +1.9 (90% distribution -29 to +31) ml min(-1) 1.73 m(-2), while GFR(MDRD) had mean bias +11.4 (-45 to +51) ml min(-1) 1.73 m(-2). With exposure to clamped hyperglycaemia, the mean increase in GFR(CYSTATIN C) (+17.5 ± 13.5 ml min(-1) 1.73 m(-2) ) reflected that observed with GFR(INULIN) (+15.3 ± 28.1 ml min(-1) 1.73 m(-2), P = 0.74), while GFR(MDRD) demonstrated a mean decline of -4.4 ± 33.6 ml min(-1) 1.73 m(-2) (P = 0.01). In all 24 subjects in whom GFR(INULIN) increased in response to hyperglycaemia, GFR(CYSTATIN C) reflected a concordant change (sensitivity, 100%) while GFR(MDRD) increased in 10/24 (sensitivity, 42%). In the eight remaining subjects, specificity was 25 and 75% for GFR(CYSTATIN C) and GFR(MDRD), respectively.

CONCLUSION

GFR(CYSTATIN C) reflects normal and elevated renal function better than GFR(MDRD) even under the acute influences of hyperglycaemia, suggesting a role for cystatin C in clinical practice and research for the study of early renal function changes in Type 1 diabetes.

Early Diagnostic Markers for Contrast Nephropathy in Patients Undergoing Coronary Angiography

The present work aimed to prove the usage of neutrophil gelatinase-associated lipocalin (NGAL) as an early biomarker for kidney injury and to assess the relationship between NGAL and serum creatinine and cystatin C in patients with normal serum creatinine undergoing percutaneous coronary angiography. Thirty patients with normal serum creatinine undergoing coronary angiography were enrolled. Estimation of blood glucose, glycosylated hemoglobin, lipid profile, creatinine, NGAL, and cystatin C were done before coronary angiography for all patients. Serum creatinine, NGAL and cystatin C were evaluated again at 4 and 24 hours after coronary angiography. There was a significant increase in serum NGAL level 4 hours and 24 hours after coronary interventions compared to the baseline value before coronary angiography. Before coronary angiography, serum NGAL was positively correlated with serum creatinine, and cystatin C. Conclusion: Serum NGAL and cystatin C could be valuable in the detection of early renal impairment after coronary angiography.

Serum and Urinary Biomarkers Determination and Their Significance in Diagnosis of Kidney Diseases

Chronic kidney disease (CKD) is becoming a major public health problem worldwide due to the epidemic increase of patients on renal replacement therapy and their high cardiovascular morbidity and mortality. The only effective approach to this problem is prevention and early detection of CKD. In addition, despite significant improvements in therapeutics, the mortality and morbidity associated with acute kidney injury (AKI) remain high. A major reason for this is the lack of early markers for AKI, and hence an unacceptable delay in initiating therapy. Therefore, there is a pressing need to develop biomarkers (proteins and other molecules in the blood or urine) for renal disease, which might assist in diagnosis and prognosis and might provide endpoints for clinical trials of drugs designed to slow the progression of renal insufficiency. Besides serum creatinine, promising novel biomarkers for AKI include a plasma panel (neutrophil gelatinase-associated lipocalin-NGAL and cystatin C) and a urine panel (NGAL, kidney injury molecule-1, interleukin-18, cystatin C, alpha 1-microglobulin, Fetuin-A, Gro-alpha, and meprin). For CKD, these include a similar plasma panel and a urine panel (NGAL, asymmetric dimethylarginine, and liver-type fatty acid-binding protein). Increased plasma and urinary TGF-β1 levels might contribute to the development of chronic tubulointerstitial disease, indicating the possible therapeutic implications. Furthermore, to differentiate lower urinary tract infection and pyelonephritis interleukin-6 and serum procalcitonin levels were introduced. It will be important in future studies to validate the sensitivity and specificity of these biomarker panels in clinical samples from large cohorts and in multiple clinical situations.

Update on the diagnosis and management of acute kidney injury

Acute kidney injury (AKI) is an independent risk factor for morbidity and mortality. This review provides essential information for the diagnosis and management of AKI. Blood urea nitrogen and serum creatinine are used for the diagnosis of AKI. The review also focuses on recent studies on the diagnosis of AKI using the RIFLE (R-renal risk, I-injury, F-failure, L-loss of kidney function, E-end stage kidney disease) and Acute Kidney Injury Network criteria, and serum and urine AKI biomarkers. Dialysis is the only Food and Drug Administration-approved therapy for AKI. Recent studies on the dose of dialysis in AKI are reviewed.

A panel of urinary biomarkers to monitor reversibility of renal injury and a serum marker with improved potential to assess renal function

The Predictive Safety Testing Consortium's first regulatory submission to qualify kidney safety biomarkers revealed two deficiencies. To address the need for biomarkers that monitor recovery from agent-induced renal damage, we scored changes in the levels of urinary biomarkers in rats during recovery from renal injury induced by exposure to carbapenem A or gentamicin. All biomarkers responded to histologic tubular toxicities to varied degrees and with different kinetics. After a recovery period, all biomarkers returned to levels approaching those observed in uninjured animals. We next addressed the need for a serum biomarker that reflects general kidney function regardless of the exact site of renal injury. Our assay for serum cystatin C is more sensitive and specific than serum creatinine (SCr) or blood urea nitrogen (BUN) in monitoring generalized renal function after exposure of rats to eight nephrotoxicants and two hepatotoxicants. This sensitive serum biomarker will enable testing of renal function in animal studies that do not involve urine collection.

Urinary clusterin, cystatin C, beta2-microglobulin and total protein as markers to detect drug-induced kidney injury

Earlier and more reliable detection of drug-induced kidney injury would improve clinical care and help to streamline drug-development. As the current standards to monitor renal function, such as blood urea nitrogen (BUN) or serum creatinine (SCr), are late indicators of kidney injury, we conducted ten nonclinical studies to rigorously assess the potential of four previously described nephrotoxicity markers to detect drug-induced kidney and liver injury. Whereas urinary clusterin outperformed BUN and SCr for detecting proximal tubular injury, urinary total protein, cystatin C and beta2-microglobulin showed a better diagnostic performance than BUN and SCr for detecting glomerular injury. Gene and protein expression analysis, in-situ hybridization and immunohistochemistry provide mechanistic evidence to support the use of these four markers for detecting kidney injury to guide regulatory decision making in drug development. The recognition of the qualification of these biomarkers by the EMEA and FDA will significantly enhance renal safety monitoring.

The assessment, serial evaluation, and subsequent sequelae of acute kidney injury (ASSESS-AKI) study: design and methods

Background

The incidence of acute kidney injury (AKI) has been increasing over time and is associated with a high risk of short-term death. Previous studies on hospital-acquired AKI have important methodological limitations, especially their retrospective study designs and limited ability to control for potential confounding factors.

Methods

The Assessment, Serial Evaluation, and Subsequent Sequelae of Acute Kidney Injury (ASSESS-AKI) Study was established to examine how a hospitalized episode of AKI independently affects the risk of chronic kidney disease development and progression, cardiovascular events, death, and other important patient-centered outcomes. This prospective study will enroll a cohort of 1100 adult participants with a broad range of AKI and matched hospitalized participants without AKI at three Clinical Research Centers, as well as 100 children undergoing cardiac surgery at three Clinical Research Centers. Participants will be followed for up to four years, and will undergo serial evaluation during the index hospitalization, at three months post-hospitalization, and at annual clinic visits, with telephone interviews occurring during the intervening six-month intervals. Biospecimens will be collected at each visit, along with information on lifestyle behaviors, quality of life and functional status, cognitive function, receipt of therapies, interim renal and cardiovascular events, electrocardiography and urinalysis.

Conclusions

ASSESS-AKI will characterize the short-term and long-term natural history of AKI, evaluate the incremental utility of novel blood and urine biomarkers to refine the diagnosis and prognosis of AKI, and identify a subset of high-risk patients who could be targeted for future clinical trials to improve outcomes after AKI.

Urinary biomarkers in the clinical prognosis and early detection of acute kidney injury

BACKGROUND AND OBJECTIVES

Several novel urinary biomarkers have shown promise in the early detection and diagnostic evaluation of acute kidney injury (AKI). Clinicians have limited tools to determine which patients will progress to more severe forms of AKI at the time of serum creatinine increase. The diagnostic and prognostic utility of novel and traditional AKI biomarkers was evaluated during a prospective study of 123 adults undergoing cardiac surgery.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Urinary neutrophil gelatinase-associated lipocalin (NGAL), cystatin C (CyC), kidney injury molecule-1 (KIM-1), hepatocyte growth factor (HGF), π-glutathione-S-transferase (π-GST), α-GST, and fractional excretions of sodium and urea were all measured at preoperative baseline, postoperatively, and at the time of the initial clinical diagnosis of AKI. Receiver operator characteristic curves were generated and the areas under the curve (AUCs) were compared.

RESULTS

Forty-six (37.4%) subjects developed AKI Network stage 1 AKI; 9 (7.3%) of whom progressed to stage 3. Preoperative KIM-1 and α-GST were able to predict the future development of stage 1 and stage 3 AKI. Urine CyC at intensive care unit (ICU) arrival best detected early stage 1 AKI (AUC = 0.70, P < 0.001); the 6-hour ICU NGAL (AUC = 0.88; P < 0.001) best detected early stage 3 AKI. π-GST best predicted the progression to stage 3 AKI at the time of creatinine increase (AUC = 0.86; P = 0.002).

CONCLUSION

Urinary biomarkers may improve the ability to detect early AKI and determine the clinical prognosis of AKI at the time of diagnosis.

Structural characterization of glycoprotein NGAL, an early predictive biomarker for acute kidney injury

Neutrophil gelatinase-associated lipocalin (NGAL) is a promising new renal biomarker that can reduce the time to diagnose acute kidney injury (AKI). There is little information available about complex glycans on NGAL. Detailed structural characterization of NGAL is necessary to understand the structural variability of NGAL used as a standard in the NGAL immunoassay. This study demonstrated that 7-9% of mutant (C87S) recombinant NGAL was N-glycosylated and no O-glycosylation was detected. The NGAL sequence was confirmed by nanoLC/MS/MS following in gel and in solution trypsin digestion, and the N-glycosylation site was localized by MS/MS. Six different mutant recombinant NGAL samples (samples A-F) were analyzed in this study; however, these samples demonstrated two different glycan patterns. Forty-one N-glycans were detected in sample A and the more abundant N-glycans were unsialylated. Forty-three N-glycans were detected in sample F and the more abundant N-glycans were sialylated. Each of the other four samples (B-E) had a similar N-glycan pattern as sample F.