Early detection of acute renal failure by serum cystatin C

Effect of malnutrition on serum creatinine and cystatin C levels

The concentration of cystatin C has been shown to be independent of age, gender and height, but the effect of malnutrition has not been studied. Levels of serum creatinine and cystatin C were estimated in 77 malnourished and 77 normally nourished boys between 2 years and 6 years of age without evidence of renal disease. The mean (95% confidence interval) serum creatinine level in the malnourished boys was significantly lower than that in the normally nourished boys [0.42 (0.38-0.45) mg/dl and 0.51 (0.48-0.55)] mg/dl, respectively, (P < 0.01)]. The mean level of serum cystatin C was 1.05 (0.94-1.17) mg/l and 1.12 (1.01-1.24) mg/l, respectively, in normally nourished and malnourished boys (P = 0.35). Mean glomerular filtration rate (GFR) estimated by the Schwartz equation in the malnourished boys was significantly higher than that in normally nourished children [141.8 (123.3-160.2) ml/min per 1.73 m(2) body surface area and 119.4 (109.3-129.5) ml/min per 1.73 m(2) body surface area], respectively (P = 0.04). However, the mean cystatin C-derived GFR was similar in the malnourished and normally nourished boys [99.70 (85.8-113.5) ml/min per 1.73 m(2) and 109.2 (94.4-124.0) ml/min per 1.73 m(2)], respectively (P = 0.35). The mean bias between GFR estimates using Bland and Altman analysis was greater in the malnourished children than in the normally nourished children (32.3% and 17.6%, respectively) (P = 0.15). Serum creatinine levels are lower in malnourished children and lead to overestimation of GFR, while cystatin C levels are unaffected.

Could neutrophil-gelatinase-associated lipocalin and cystatin C predict the development of contrast-induced nephropathy after percutaneous coronary interventions in patients with stable angina and normal serum creatinine values?

The value of neutrophil-gelatinase-associated lipocalin (NGAL) was highlighted as a novel biomarker for the detection of acute renal failure. We tested the hypothesis whether NGAL could represent an early biomarker of contrast-induced nephropathy (CIN) in 100 patients with normal serum creatinine values undergoing percutaneous coronary interventions (PCI). In addition, we assessed serum and urinary NGAL in relation to cystatin C, estimated glomerular filtration rate, and serum and urinary creatinine in these patients. We measured urinary and serum NGAL values before and 2, 4, 8, 24, and 48 h after the PCI. We found a significant rise in serum NGAL levels 2, 4, and 8 h after the PCI and in urinary NGAL values 4, 8, and 24 h after a PCI procedure. Cystatin C rose significantly 24 h after the procedure. The prevalence of CIN was 11%. The NGAL levels were significantly higher 2 h after the PCI (serum NGAL) or 4 h after the PCI (urinary NGAL), whereas the cystatin C values were higher only 8 and 24 h after a PCI procedure in patients with CIN. In multivariate analysis, only serum creatinine was a predictor of serum NGAL before a PCI. NGAL may represent a sensitive early biomarker of renal impairment after PCI. Serum creatinine level, the presence of diabetes, and the duration of the PCI may affect serum NGAL values and kidney function following a PCI procedure.

Urine proteomics: the present and future of measuring urinary protein components in disease

For centuries, physicians have attempted to use the urine for noninvasive assessment of disease. Today, urinalysis, in particular the measurement of proteinuria, underpins the routine assessment of patients with renal disease. More sophisticated methods for assessing specific urinary protein losses have emerged; however, albumin is still the principal urinary protein measured. Changes in the pattern of urinary protein excretion are not necessarily restricted to nephrourological disease; for instance, the appearance of beta-human chorionic gonadotropin in the urine of pregnant women is the basis for all commercially available pregnancy kits. Similarly, microalbuminuria is a clinically important marker not only of early diabetic nephropathy but also of concomitant cardiovascular disease. With the emergence of newer technologies, in particular mass spectrometry, it has become possible to study urinary protein excretion in even more detail. A variety of techniques have been used both to characterize the normal complement of urinary proteins and also to identify proteins and peptides that may facilitate earlier detection of disease, improve assessment of prognosis and allow closer monitoring of response to therapy. Such proteomics-based approaches hold great promise as the basis for new diagnostic tests and as the means to better understand disease pathogenesis. In this review, we summarize the currently available methods for urinary protein analysis and describe the newer approaches being taken to identify urinary biomarkers.

Novel approaches to assessing renal function in cirrhotic liver disease

Renal dysfunction is common in patients with end-stage liver disease. Etiological factors include conditions as diverse as acute tubular necrosis, immunoglobulin A nephropathy and hepatorenal syndrome. Current standard tests of renal function, such as measurement of serum urea and creatinine levels, are inaccurate as the synthesis of these markers is affected by the native liver pathology. This article reviews novel markers of renal function and their potential use in patients with liver disease.

I.v. N-acetylcysteine and emergency CT: use of serum creatinine and cystatin C as markers of radiocontrast nephrotoxicity

OBJECTIVE

The purpose of this study was to assess the effect of i.v. administration of N-acetylcysteine (NAC) on serum levels of creatinine and cystatin C, two markers of renal function, in patients with renal insufficiency who undergo emergency contrast-enhanced CT.

SUBJECTS AND METHODS

Eighty-seven adult patients with renal insufficiency who underwent emergency CT were randomized to two groups. In the first group, in addition to hydration, patients received a 900-mg injection of NAC 1 hour before and another immediately after injection of iodine contrast medium. Patients in the second group received hydration only. Serum levels of creatinine and cystatin C were measured at admission and on days 2 and 4 after CT. Nephrotoxicity was defined as a 25% or greater increase in serum creatinine or cystatin C concentration from baseline value.

RESULTS

A 25% or greater increase in serum creatinine concentration was found in nine (21%) of 43 patients in the control group and in two (5%) of 44 patients in the NAC group (p = 0.026). A 25% or greater increase in serum cystatin C concentration was found in nine (22%) of 40 patients in the control group and in seven (17%) of 41 patients in the NAC group (p = 0.59).

CONCLUSION

On the basis of serum creatinine concentration only, i.v. administration of NAC appears protective against the nephrotoxicity of contrast medium. No effect is found when serum cystatin C concentration is used to assess renal function. The effect of NAC on serum creatinine level remains unclear and may not be related to a renoprotective action.

Cystatin C blood level as a risk factor for death after heart surgery

AIMS

Pre-operative renal dysfunction is a known risk factor for mortality and morbidity after heart surgery. Despite limited accuracy, serum creatinine is widely used to estimate glomerular filtration rate (GFR). Cystatin C is more accurate for assessing GFR. The aim of the present study was to assess associations between GFR estimated from serum cystatin C levels before heart surgery and hospital mortality, hospital morbidity, and 1 year mortality.

METHODS AND RESULTS

In a prospective single-centre observational study, clinical risk factors for morbidity and mortality were recorded and serum creatinine and cystatin C levels were measured in patients admitted for heart surgery. Hospital mortality and morbidity and 1 year mortality were recorded. Over an 8 month period, 499 patients were screened, among whom 376 (74.5%) were included in the study. Hospital mortality was 5.6% (21 patients) and 1 year mortality was 10.2%. Hospital morbidity, defined by a length of stay above the 75th percentile, was 22.1% (83 patients). In the multivariable analysis, GFR estimated from serum cystatin C, but not GFR estimated from serum creatinine, was an independent risk factor for hospital morbidity/mortality (odds ratio per 10 mL/min of GFR decrease, 1.20 (1.07-1.34), P = 0.001) and for 1 year mortality (hazards ratio per 10 mL/min of GFR decrease, 1.26 (1.09-1.46), P = 0.002).

CONCLUSION

Pre-operative GFR estimation from serum cystatin C may provide a better risk assessment than pre-operative GFR estimation from serum creatinine in patients scheduled for heart surgery.

Replacement of 24-h creatinine clearance by 2-h creatinine clearance in intensive care unit patients: a single-center study

OBJECTIVE

To estimate the usefulness of 2-h creatinine clearance (CrCl) in the ICU and define variables that may reduce agreement.

DESIGN

Prospective study.

SETTING

Polyvalent ICU of a university hospital.

PATIENTS

359 patients.

INTERVENTIONS

We compared 24-h CrCl (CrCl-24h), as the standard measure, with 2-h CrCl (CrCl-2h) (at the start of the period) and the Cockroft-Gault equation (Ck-G).

MEASUREMENTS AND RESULTS

The 2-h sample was lost in two patients (0.6%) and the 24-h sample was lost in 50 patients (13.9%). The mean Ck-G was 87.4+/-3.05, with CrCl-2h 109.2+/-4.46 and CrCl-24h 100.9+/-4.21 ml/min/1.73 m2 (r2 of 0.88 for CrCl-2h and 0.84 for Ck-G). The differences from ClCr-24h were 21.8+/-3.3 (p<0.001) for the Ck-G and 8.3+/-2.6 (p<0.05) for CrCl-2h (p<0.05). In the subgroup of patients with CrCl-24h<100 ml/min/1.73 m2, the CrCl-24h value was 52.9+/-2.71 vs. 51.6+/-2.14 for CrCl-2h (p=ns) and 57.6+/-2.56 (p<0.001) for the Ck-G. Patients with CrCl<100 ml/min only showed variability in hyperglycemia during the 24-h period.

CONCLUSIONS

In intensive care patients, 24-h CrCl results in a large proportion of non-valid determinations, even under conditions of close monitoring. Two-hour CrCl is an adequate substitute, even in patients who are unstable or who have irregular diuresis where a 24-h collection is impossible. The Cockroft-Gault equation seems less useful in this setting.

The kidney in the critically ill

Acute kidney injury (AKI) is a common and serious complication in the intensive care setting. It seldom occurs in isolation, but is mostly part of a multiple organ dysfunction syndrome. The pathogenesis is frequently multifactorial, with sepsis contributing to 50% of the cases.The development of AKI in critically-ill patients is "bad news": patients with AKI have a high morbidity and mortality. In addition, AKI, even in its mildest from, is not only a marker of illness severity but appears to be independently associated with mortality. Prevention of AKI is therefore a major goal to improve outcome of critically-ill patients. Treatment of established AKI is largely supportive. The optimal modality for renal replacement therapy in critically-ill patients still remains a matter of debate). The majority of survivors recover renal function.

NGAL (neutrophil gelatinase-associated lipocalin) and cystatin C: are they good predictors of contrast nephropathy after percutaneous coronary interventions in patients with stable angina and normal serum creatinine?

The aim of the study was to assess whether NGAL and cystatin C could predict contrast-induced nephropathy in non-diabetic patients (n=60, mean age 60+/-11 years) with normal serum creatinine undergoing elective PCI. We found a significant rise in serum NGAL after 2, 4 and 8 h, and in urinary NGAL after 4, 8 and 24 h after PCI. Cystatin C rose significantly 8 and 24 h after the procedure. Prevalence of CIN was 10%. We found 90% sensitivity and 74% specificity of serum and 76% sensitivity and 80% specificity of urinary NGAL increase. NGAL may represent a sensitive early biomarkers of renal impairment after PCI.

[Extracorporeal blood purification in the intensive care units]

Mortality remains high in intensive care patients with renal failure requiring extra corporeal blood purification. This article reviews the recent data that have led to the improvement of the care for such patients. We will discuss the criteria to determine the choice of the technique (intermittent or continuous), of the membrane, of the prescribing dose, and the type of anticoagulation and when to initiate such a treatment.

[Evaluation of the renal function in cardiac surgery with CPB: role of the cystatin C and the calculated creatinine clearance]

OBJECTIVES

The evaluation of the renal function in cardiac surgery is difficult. The gold standard remains the creatinine clearance in clinical practice. Cystatin C was recently proposed in order to evaluate the renal function. The aim of our study was to evaluate the cystatin C in cardiac surgery with CPB.

PATIENTS AND METHODS

After informed consent and ethical committee agreement, 60 patients operated in cardiac surgery with CPB were prospectively included. Cystatin C,measured and calculated (Cockcroft and MDRD methods) creatinine were compared with the Student t-test and with the Bland and Altman method. p<0,05 was considered as a significant threshold.

RESULTS

The reproducibility of the calculated creatinine clearance was better when the urinary collecting time was below 400 minutes. The estimation of the creatinine clearance by the Cockcroft and MDRD methods is better when the clearance is low. A significant correlation between the creatinine clearance and the cystatin C does exist, but the correlation coefficient was low. In case of acute renal dysfunction, the increase of the creatinine occurred earlier than the increase of the cystatin C.

CONCLUSION

In cardiac surgery with CPB, the evaluation of the renal function was not improved by the cystatin C.

Acute Renal Injury and Dysfunction Following Elective Abdominal Aortic Surgery

OBJECTIVES

To evaluate the incidence of kidney injury and acute renal dysfunction (ARD) and associated risk factors in open abdominal aortic surgery.

MATERIALS AND METHODS

69 patients undergoing elective infrarenal aortic repair were included in a prospective study. Anaesthesia and haemodynamic management were standardised targeting a mean arterial pressure (MAP) of 70-90 mmHg, pulmonary artery occlusion pressure of 12-14 mmHg and cardiac index >or=2.4 l/min/m(2). Urinary albumin-creatinine and N-acetyl-B-D-glucosaminidase-creatinine ratios were measured as indicators of kidney injury. The definition of ARD was based on the RIFLE criteria.

RESULTS

Kidney injury was found in most patients. ARD developed in 22% of the patients, and acute renal failure in 4%. The patients with ARD were older, and had lower plasma creatinine and estimated GFR before surgery. ARD was associated with intraoperative hypotension (MAP <60 mmHg >15 min), low cardiac index (<2.4 l/min/m(2)), rhabdomyolysis, and early reoperation. Intraoperative hypotension and postoperative low cardiac output were independent risk factors for ARD in multivariate analysis.

CONCLUSIONS

Kidney injury occurs in most patients undergoing infrarenal aortic surgery, but only 22% develop acute renal dysfunction. Hypotension and low cardiac output are risk factors that could be avoided by optimizing perioperative management.

Serum cystatin C as a marker of glomerular filtration rate

PURPOSE OF REVIEW

Glomerular filtration rate is widely accepted as the best overall measure of kidney function. Currently available methods to estimate glomerular filtration rate have strengths and limitations. Cystatin C is a novel endogenous filtration marker being considered as a potential replacement for serum creatinine. This review summarizes the currently available glomerular filtration rate estimating equations based on cystatin C and the literature comparing cystatin C and creatinine as filtration markers.

RECENT FINDINGS

In most cystatin C estimating equations, inclusion of age and sex did not substantially improve their performance. Equations yield different glomerular filtration rate estimates for the same level of cystatin C. Variation among equations may be due to differences among the assays or populations in the individual studies. Studies comparing cystatin C with creatinine or creatinine-based estimating equations show heterogeneous results, with some showing improved performance and others showing equivalent performance even in similar populations. These heterogeneous results may be due to inappropriate comparisons between equations developed in one population with those developed in another, or to the differences between assays or population characteristics.

SUMMARY

Cystatin C shows promise as an alternative to serum creatinine but several important questions remain before it can be recommended for use in clinical practice.

N-acetylcysteine to ameliorate acute renal injury in a rat cardiopulmonary bypass model

OBJECTIVE

Oxidative stress and systemic inflammation response contribute to acute renal injury post cardiac surgery. We hypothesized that administration of the antioxidant N-acetylcysteine would be beneficial to renal function after cardiopulmonary bypass in a rat model.

METHODS

Male Sprague-Dawley rats were divided into four groups (each n = 6): sham group, cardiopulmonary bypass group, and two N-acetylcysteine-treated cardiopulmonary bypass groups (bolus doses of 200 and 500 mg/kg in cardiopulmonary bypass prime). Blood samples were collected at the beginning of cardiopulmonary bypass, at the cessation of cardiopulmonary bypass, and at 2 and 12 postoperative hours. The kidneys were harvested at 12 postoperative hours.

RESULTS

Serum creatinine and cystatin C continuously increased in all cardiopulmonary bypass groups (P < .05 within groups). Tubular dilatation, tubular necrosis, and vacuole formation were found in epithelial cells in histomorphologic studies of the cardiopulmonary bypass groups, but N-acetylcysteine significantly reversed these effects (P < .05 between groups). Compared with the sham group, the reduced glutathione hormone content and the superoxide dismutase and catalase activities decreased in the cardiopulmonary bypass groups (P < .01). N-acetylcysteine-treated groups had higher levels of these antioxidants than the untreated bypass group (P < .05). Renal malondialdehyde, tumor necrosis factor alpha, and nuclear factor kappaB were notably increased in all cardiopulmonary bypass groups relative to the sham group (P < .01), and N-acetylcysteine attenuated these changes dose dependently.

CONCLUSION

Administration of the antioxidant N-acetylcysteine preserved renal function after cardiopulmonary bypass dose dependently. Furthermore, oxidative stress and systemic inflammation were significantly reduced in the treated animals.

Serum neutrophil gelatinase-associated lipocalin as a marker of renal function in children with chronic kidney disease

Very few biomarkers exist for monitoring chronic kidney disease (CKD). We have recently shown that serum neutrophil gelatinase-associated lipocalin (NGAL) represents a novel biomarker for early identification of acute kidney injury. In this study, we hypothesized that serum NGAL may also represent a biomarker for the quantitation of CKD. Forty-five children with CKD stages 2-4 were prospectively recruited for measurement of serum NGAL, serum cystatin C, glomerular filtration rate (GFR) by Ioversol clearance, and estimated GFR (eGFR) by Schwartz formula. Serum NGAL significantly correlated with cystatin C (r=0.74, P<0.000). Both NGAL and cystatin C significantly correlated with measured GFR (r=0.62, P<0.000; and r=0.71, P<0.000, respectively) as well as with eGFR (r=0.66, P<0.000 and r=0.59, P<0.000, respectively). At GFR levels of >or=30 ml/min per 1.73 m(2), serum NGAL, cystatin C, and eGFR were all significantly correlated with measured GFR. However, in subjects with lower GFRs (<30 ml/min per 1.73 m(2)), serum NGAL levels correlated best with measured GFR (r=0.62), followed by cystatin C (r=0.41). We conclude that (a) both serum NGAL and cystatin C may prove useful in the quantitation of CKD, and (b) by correlation analysis, NGAL outperforms cystatin C and eGFR at lower levels of measured GFR.

Acute kidney injury in the ICU: time has come for an early biomarker kit!

Early recognition of acute kidney injury (AKI) in the intensive care unit (ICU) remains a critical problem, with a rising incidence and a high mortality rate. As a consequence, the actual lack of an early and effective biomarker results in a significant delay in initiating appropriate therapy. The accurate diagnosis of AKI is especially problematic in critically-ill patients, in whom we know that renal function is in an unsteady state; therefore the validity of creatinine-based baseline assessment measures is reduced. Because the rationale for assessing AKI markers in critically-ill patients is strong at the present time, researchers are stimulated to establish a multidimensional AKI classification system. This system should in essence grade AKI severity. The most widely referenced classification is the RIFLE system. Thus, early recognition of AKI, well before changes in serum creatinine occur, has come under intensive research, because it is evidenced that even small increases in serum creatinine are associated with an increase in patient mortality. The development of a biomarker kit in which several early markers with different characteristics are combined, is essential. Multi-centre, randomized studies indicate a potential for early biomarkers able to diagnose AKI 48 hours before creatinine changes. In conclusion, time has come to leave serum creatinine behind as a marker of renal function in patients with AKI on the ICU. Only then will we be able to offer early goal-directed therapy for the kidney in the ICU setting.

Mechanistic biomarkers for cytotoxic acute kidney injury

Acute kidney injury is a common condition and is associated with a high mortality rate. It has been recognised that routinely used measures of renal function, such as levels of blood urea nitrogen and serum creatinine, increase significantly only after substantial kidney injury occurs and then with a time delay. Insensitivity of such tests delays the diagnosis in humans, making it particularly challenging to administer putative therapeutic agents in a timely fashion. Furthermore, this insensitivity affects the evaluation of toxicity in preclinical studies by allowing drug candidates, which have low, but nevertheless important, nephrotoxic side effects in animals, to pass the preclinical safety criteria only to be found to be clinically nephrotoxic with great human costs. This review presents the current status of sensitive and specific biomarkers to detect preclinical and clinical renal injury and summarises the techniques used to quantitate these biomarkers in biological fluids.

CRITICAL CARE ISSUES FOR THE NEPHROLOGIST: The Epidemiology and Outcome of Acute Renal Failure and the Impact on Chronic Kidney Disease

Acute renal failure (ARF) is a common condition, especially among the critically ill, and confers a high mortality. Recent publications have highlighted changes in the epidemiology and improvement in mortality that was long thought to be static despite improvements in clinical care. The incidence of ARF is increasing. Efforts, such as the Acute Dialysis Quality Initiative, are being undertaken to establish a consensus definition of ARF, and to distinguish between varying degrees of acute kidney injury. Data are emerging to allow comparison of the epidemiology of ARF across institutions internationally. There is ongoing recognition of the important interaction between ARF and chronic kidney disease. Two brief case reports are offered to help frame the context and clinical impact of this disorder, followed by a review of some of the recent literature that addresses these points.

Acute kidney injury: epidemiology and diagnostic criteria

PURPOSE OF REVIEW

To review recent advances in the definitions and diagnostic criteria for acute renal failure and acute kidney injury. To explore how these changes impact the epidemiology and clinical implications for patients in the intensive care unit.

RECENT FINDINGS

Recently published consensus criteria for the definition of acute renal failure/acute kidney injury have led to significant changes in how we think about this disorder. Studies from around the world, both in and out of the intensive care unit, have shown a dramatic incidence of acute kidney injury and high associated mortality. This review considers these new findings and their historical context, and attempts to shed new light on this old problem.

SUMMARY

Small changes in kidney function in hospitalized patients are important and impact on outcome. RIFLE criteria provide a uniform definition of acute kidney injury and are increasingly used in literature.

Cystatin C as a reliable marker of renal function following heart valve replacement surgery with cardiopulmonary bypass

BACKGROUND

Little is known about serum cystatin C as a marker of renal function in cardiac surgery patients. The aim of this study was to assess its utility post cardiopulmonary bypass (CPB).

METHODS

60 heart valve replacement patients were enrolled, and 26 of them had low-dose corticosteroid treatment on the first 3 days postoperatively. Serum creatinine, serum cystatin C and 24-h creatinine clearance rate (CCR) adjusted by body surface area were determined preoperation, days 1, 2, 3, 7 post operation.

RESULTS

Serum creatinine increased and peaked at day 3 postoperatively, while cystatin C peaked at day 2, and the adjusted CCR also reached a minimum at day 2. The inverse of cystatin C correlated better with CCR than that of creatinine (r=0.751 vs. 0.629). Using adjusted CCR as "golden standard", cystatin C was superior to creatinine in diagnosing renal dysfunction (area under the curve [AUC] for cystatin C 0.876, 95% confidence interval 81.8-93.4; AUC for creatinine 0.801, 95% confidence interval 72.5-87.7; p=0.045). Low-dose corticosteroid treatment has no significant effect on cystatin C.

CONCLUSION

In agreement with many other investigators, the present findings support cystatin C is a reliable marker of renal function. It is superior to creatinine in patients post CPB.

How to estimate GFR-serum creatinine, serum cystatin C or equations?

Plasma or serum creatinine is the most commonly used diagnostic marker for the estimation of glomerular filtration rate (GFR) in clinical routine. Due to substantial pre-analytical and analytical interferences and limitations, creatinine cannot be considered accurate. Besides, the diagnostic sensitivity to detect moderate GFR reduction is insufficient. Equations to estimate GFR based on serum creatinine have been introduced, which included anthropometric data to compensate for the limitations of creatinine. Most validated and applied are the MDRD and the Cockcroft-Gault equation for adults, and the Schwartz equation for children. These equations can be calculated at the bedside or issued by the laboratory and provide accurate GFR estimates from 20 to 60 mL/min/1.73 m(2) with good accuracy but moderate to poor bias and precision. Further limiting is the lack of creatinine reference methods and of calibration material. Lately, the low molecular weight protein cystatin C was introduced as a GFR estimate superior to creatinine. In particular, serum cystatin C is sensitive to detect mild GFR reduction between 60 and 90 mL/min/1.73 m(2). However, no reference method and no uniform calibration material exist for cystatin C either. Further limitations are the effect of thyroid dysfunction, of high glucocorticoid doses and potentially the presence of cardiovascular diseases on cystatin C levels. To evade these obstacles and to further improve GFR estimation, cystatin C-based equations have been proposed, which seem to be superior to creatinine-based ones. However, this issue requires further evaluation. We propose a panel of GFR markers to facilitate the detection of reduced GFR at various stages and in different populations; this however needs to be extended and refined in the near future. In principle, clinicians should be aware of the limitations of and cautioned not to overrate estimated GFR by single markers or calculated by equations and should not entirely rely on GFR estimates to make precise clinical decisions.

Protein biomarkers associated with acute renal failure and chronic kidney disease

Acute renal failure (ARF) as well as chronic kidney disease (CKD) are currently categorized according to serum creatinine concentrations. Serum creatinine, however, has shortcomings because of its low predictive values. The need for novel markers for the early diagnosis and prognosis of renal diseases is imminent, particularly for markers reflecting intrinsic organ injury in stages when glomerular filtration is not impaired. This review summarizes protein markers discussed in the context of ARF as well as CKD, and provides an overview on currently available discovery results following 'omics' techniques. The identified set of candidate marker proteins is discussed in their cellular and functional context. The systematic review of proteomics and genomics studies revealed 56 genes to be associated with acute or chronic kidney disease. Context analysis, i.e. correlation of biological processes and molecular functions of reported kidney markers, revealed that 15 genes on the candidate list were assigned to the most significant ontology groups: immunity and defence. Other significantly enriched groups were cell communication (14 genes), signal transduction (22 genes) and apoptosis (seven genes). Among 24 candidate protein markers, nine proteins were also identified by gene expression studies. Next generation candidate marker proteins with improved diagnostic and prognostic values for kidney diseases will be derived from whole genome scans and protemics approaches. Prospective validation still remains elusive for all proposed candidates.

Biomarkers of acute renal injury and renal failure

Acute renal failure (ARF) is a frequent problem in the intensive care unit and is associated with a high mortality. Early recognition could help clinical management, but current indices lack sufficient predictive value for ARF. Therefore, there might be a need for biomarkers in detecting renal tubular injury and/or dysfunction at an early stage before a decline in glomerular filtration rate is noted by an increased serum creatinine. A MEDLINE/PubMed search was performed, including all articles about biomarkers for ARF. All publication types, human and animal studies, or subsets were searched in English language. An extraction of relevant articles was made for the purpose of this narrative review. These biomarkers include tubular enzymes (alpha- and pi-glutathione S-transferase, N-acetyl-glucosaminidase, alkaline phosphatase, gamma-glutamyl transpeptidase, Ala-(Leu-Gly)-aminopeptidase, and fructose-1,6-biphosphatase), low-molecular weight urinary proteins (alpha1- and beta2-microglobulin, retinol-binding protein, adenosine deaminase-binding protein, and cystatin C), Na+/H+ exchanger, neutrophil gelatinase-associated lipocalin, cysteine-rich protein 61, kidney injury molecule 1, urinary interleukins/adhesion molecules, and markers of glomerular filtration such as proatrial natriuretic peptide (1-98) and cystatin C. These biomarkers, detected in urine or serum shortly after tubular injury, have been suggested to contribute to prediction of ARF and need for renal replacement therapy. However, excretion of these biomarkers may also increase after reversible and mild dysfunction and may not necessarily be associated with persistent or irreversible damage. Large prospective studies in human are needed to demonstrate an improved outcome of biomarker-driven management of the patient at risk for ARF.

Serum cystatin C and left ventricular diastolic dysfunction in children with chronic kidney disease

Previous studies indicate that serum cystatin C predicts incident heart failure in older adults. Children with chronic kidney disease (CKD) develop left ventricular (LV) diastolic dysfunction, often the initial abnormality of cardiac function. We hypothesized that cystatin C might predict LV diastolic dysfunction in children with CKD. Fifty-seven subjects, aged 6-21 years, with stage 2-4 CKD underwent echocardiography. Diastole was assessed from transmitral Doppler [maximum early (E wave) and late (A wave) diastolic flow velocities (E/A ratio)] and from tissue Doppler [septal mitral annular peak velocities (E')]. LV filling pressures were determined, using a ratio of E/E'. Fourteen (25%) patients had low E' and 15 (26%) had high E/E'. Children with abnormal E' or E/E' had significantly higher cystatin C levels than children with normal indices (P<0.05). Neither serum creatinine nor measured glomerular filtration rate (GFR) significantly correlated with E' or E/E'. Stepwise multiple regression analysis showed that cystatin C (beta=-0.825, P=0.023) and left ventricular mass (LVM) index (beta=0.099, P=0.006) independently predicted E'; LVM index independently predicted E/E' (beta=0.0173, P=0.01). We conclude that, in contrast to measured GFR or serum creatinine level, elevated serum cystatin C might be associated with diastolic dysfunction in children with CKD.

Cystatin C, kidney function and cardiovascular disease

Cystatin C, an endogenous low-molecular-weight marker of glomerular filtration rate, has recently been shown to be associated with future cardiovascular disease in healthy elderly populations and patients with documented atherosclerosis in a dose-dependent manner that possibly reflects a very early stage of chronic renal dysfunction. At the same time, local cystatin C deficiency has been demonstrated in atherosclerotic and aneurismal lesions, suggesting a protective role of cystatin C in the vessel wall, possibly in concert with TGF-beta1. Although cystatin C is not an acute phase reactant, large epidemiological studies have documented a highly significant association between serum cystatin C and mildly increased C-reactive protein (CRP) levels, the hallmark of the chronic inflammatory state associated with atherosclerosis and chronic renal failure. Since cystatin C is produced by all nucleated cells, it is unlikely that local variations in cystatin C synthesis in diseased arteries--rather than global cystatin C production and renal elimination--should determine its serum concentration. Consequently, the present review proposes microinflammation as the unifying concept for both lines of evidence.

Defining Acute Renal Failure: RIFLE and Beyond: Table 1

The introduction of the RIFLE classification has increased the conceptual understanding of the acute kidney injury (AKI) syndrome, and this classification has been successfully tested in a number of clinical studies. This review discusses the strengths and weaknesses of the RIFLE classification and suggests additional parameters to broaden future definitions of AKI. These definitions should not only focus on kidney function alone, but also include parameters describing the origin of the patient, the most important causal factors responsible for AKI and information on the pre-existing kidney function. This more complete definition should lead to a decrease in the variability of the results of epidemiological studies and of future clinical trials in AKI populations.

Erythropoietin and Acute Renal Failure

The hemopoietic growth factor erythropoietin (EPO) has been recognized to be a multifunctional cytokine that plays a key role in ischemic preconditioning in the brain and heart. The EPO receptor is expressed widely in the kidney, and we review the important findings from the use of EPO in experimental models of acute renal failure that show that EPO reduces tubular cell death and hence the dysfunction induced by ischemia reperfusion injury, and we explore how these observations may be translated into the clinical arena.

Pediatric acute kidney injury: it's time for real progress

Mortality and morbidity from acute renal failure has not improved in pediatric or adult patients over the past 40 years. This lack of improvement stems from varied definitions for acute renal failure (ARF), changes in ARF epidemiology, and the reliance on changes in serum creatinine for ARF diagnosis. Significant research has occurred in the past 5 years to standardize ARF definitions, recognize ARF earlier, discover urinary biomarkers of early renal insult, and more optimally manage patients with ARF. As a result, changes in nomenclature from ARF to acute kidney injury and earlier institution of renal replacement therapy may lead to improvements in patient outcome. The aim of this editorial is to provide a description of the state of the art in pediatric ARF diagnosis and management by highlighting recent significant clinical and research progress.

Influence of fluid resuscitation on renal microvascular PO2 in a normotensive rat model of endotoxemia

Introduction

Septic renal failure is often seen in the intensive care unit but its pathogenesis is only partly understood. This study, performed in a normotensive rat model of endotoxemia, tests the hypotheses that endotoxemia impairs renal microvascular PO₂ (μPO₂) and oxygen consumption (VO_2,ren), that endotoxemia is associated with a diminished kidney function, that fluid resuscitation can restore μPO₂, VO_2,ren and kidney function, and that colloids are more effective than crystalloids.

Methods

Male Wistar rats received a one-hour intravenous infusion of lipopolysaccharide, followed by resuscitation with HES130/0.4 (Voluven^®), HES200/0.5 (HES-STERIL^{® ®} 6%) or Ringer's lactate. The renal μPO₂ in the cortex and medulla and the renal venous PO₂ were measured by a recently published phosphorescence lifetime technique.

Results

Endotoxemia induced a reduction in renal blood flow and anuria, while the renal μPO₂ and VO_2,ren remained relatively unchanged. Resuscitation restored renal blood flow, renal oxygen delivery and kidney function to baseline values, and was associated with oxygen redistribution showing different patterns for the different compounds used. HES200/0.5 and Ringer's lactate increased the VO_2,ren, in contrast to HES130/0.4.

Conclusion

The loss of kidney function during endotoxemia could not be explained by an oxygen deficiency. Renal oxygen redistribution could for the first time be demonstrated during fluid resuscitation. HES130/0.4 had no influence on the VO_2,ren and restored renal function with the least increase in the amount of renal work.

Kidney NGAL is a novel early marker of acute injury following transplantation

Acute kidney injury secondary to ischemia-reperfusion in renal allografts often results in delayed graft function. We tested the hypothesis that expression of neutrophil gelatinase-associated lipocalin (NGAL) is an early marker of acute kidney injury following transplantation. Sections from paraffin-embedded protocol biopsy specimens obtained at approximately one hour of reperfusion after transplantation of 13 cadaveric (CAD) and 12 living-related (LRD) renal allografts were examined by immunohistochemistry for expression of NGAL. The staining intensity was correlated with cold ischemia time, peak post-operative serum creatinine, and dialysis requirement. There were no differences between the LRD and CAD groups in age, gender or preoperative serum creatinine. Using a scoring system of 0 (no staining) to 3 (most intense staining), NGAL expression was significantly increased in CAD specimens (2.3+/-0.8 versus 0.8+/-0.7 in LRD, p<0.001). There was a strong correlation between NGAL staining intensity and cold ischemia time (R=0.87, p<0.001). Importantly, NGAL staining in these early CAD biopsies was strongly correlated with peak postoperative serum creatinine, which occurred days later (R=0.86, p<0.001). Four patients developed delayed graft function requiring dialysis during the first week posttransplantation; all of these patients displayed the most intense NGAL staining in their first protocol biopsies. We conclude that NGAL staining intensity in early protocol biopsies represents a novel predictive biomarker of acute kidney injury following transplantation.

RIFLE criteria for acute kidney injury are associated with hospital mortality in critically ill patients: a cohort analysis

Introduction

The lack of a standard definition for acute kidney injury has resulted in a large variation in the reported incidence and associated mortality. RIFLE, a newly developed international consensus classification for acute kidney injury, defines three grades of severity – risk (class R), injury (class I) and failure (class F) – but has not yet been evaluated in a clinical series.

Methods

We performed a retrospective cohort study, in seven intensive care units in a single tertiary care academic center, on 5,383 patients admitted during a one year period (1 July 2000–30 June 2001).

Results

Acute kidney injury occurred in 67% of intensive care unit admissions, with maximum RIFLE class R, class I and class F in 12%, 27% and 28%, respectively. Of the 1,510 patients (28%) that reached a level of risk, 840 (56%) progressed. Patients with maximum RIFLE class R, class I and class F had hospital mortality rates of 8.8%, 11.4% and 26.3%, respectively, compared with 5.5% for patients without acute kidney injury. Additionally, acute kidney injury (hazard ratio, 1.7; 95% confidence interval, 1.28–2.13; P < 0.001) and maximum RIFLE class I (hazard ratio, 1.4; 95% confidence interval, 1.02–1.88; P = 0.037) and class F (hazard ratio, 2.7; 95% confidence interval, 2.03–3.55; P < 0.001) were associated with hospital mortality after adjusting for multiple covariates.

Conclusion

In this general intensive care unit population, acute kidney 'risk, injury, failure', as defined by the newly developed RIFLE classification, is associated with increased hospital mortality and resource use. Patients with RIFLE class R are indeed at high risk of progression to class I or class F. Patients with RIFLE class I or class F incur a significantly increased length of stay and an increased risk of inhospital mortality compared with those who do not progress past class R or those who never develop acute kidney injury, even after adjusting for baseline severity of illness, case mix, race, gender and age.

Consensus development in acute renal failure: The Acute Dialysis Quality Initiative

PURPOSE OF REVIEW

Although acute renal failure is both common and highly lethal in the intensive care unit, our understanding of the epidemiology and pathophysiology of acute renal failure is limited, and treatment for acute renal failure is extremely variable around the world. The general lack of consensus with regard to definitions, prevention, and treatment of acute renal failure has limited progress in this field.

RECENT FINDINGS

Consensus in acute renal failure requires establishing a framework in which intensivists, nephrologists, pharmacologists, and others who care for critically ill patients with or at risk for acute renal failure can reach consensus and develop evidence-based practice guidelines. The Acute Dialysis Quality Initiative seeks to provide an objective, dispassionate distillation of the literature and description of the current state of practice of dialysis and related therapies as they are applied to acutely ill patients. The purposes of Acute Dialysis Quality Initiative are first, to develop a consensus of opinion, with evidence where possible, on best practice; and second, to articulate a research agenda to focus on important unanswered questions.

SUMMARY

Broad consensus in the diagnosis and management of acute renal failure and in the use of blood purification in nonrenal critical illness is achievable. Standardization of definitions, practice, and research methodology is urgently needed, and specific proposals have been made by an international, interdisciplinary group.

Drug-induced acute kidney injury

PURPOSE OF REVIEW

The purpose of this review is to describe the most prevalent mechanisms of drug-induced acute kidney injury, to define the risk factors for nephrotoxicity, and to analyze the available evidence for preventive measures.

RECENT FINDINGS

Drug toxicity remains an important cause of acute kidney injury that, in many circumstances, can be prevented or at least minimized by vigilance and early intervention. Recent studies have resulted in increased insight into the subcellular mechanisms of drug nephrotoxicity. Further improvement is to be expected from the identification of early markers of nephrotoxicity and an increasing involvement of a clinical pharmacist.

SUMMARY

The main mechanisms of nephrotoxicity are vasoconstriction, altered intraglomerular hemodynamics, tubular cell toxicity, interstitial nephritis, crystal deposition, thrombotic microangiopathy, and osmotic nephrosis. Before prescribing a potentially nephrotoxic drug, the risk-to-benefit ratio and the availability of alternative drugs should be considered. Modifiable risk factors should be corrected. The correct drug dosage should be prescribed. Patients should be pre-hydrated and the glomerular filtration rate should be frequently monitored during the administration of a potentially nephrotoxic drug. Studies are needed to further elucidate the mechanisms of nephrotoxicity to design more-rational prevention and treatment strategies. Computer-based prescriber-order entry and an appropriately trained intensive care unit pharmacist are particularly helpful to minimize medication errors and adverse drug events.

Risk factors for acute renal failure: inherent and modifiable risks

PURPOSE OF REVIEW

Our purpose is to discuss established risk factors in the development of acute renal failure and briefly overview clinical markers and preventive measures.

RECENT FINDINGS

Findings from the literature support the role of older age, diabetes, underlying renal insufficiency, and heart failure as predisposing factors for acute renal failure. Diabetics with baseline renal insufficiency represent the highest risk subgroup. An association between sepsis, hypovolemia, and acute renal failure is clear. Liver failure, rhabdomyolysis, and open-heart surgery (especially valve replacement) are clinical conditions potentially leading to acute renal failure. Increasing evidence shows that intraabdominal hypertension may contribute to the development of acute renal failure. Radiocontrast and antimicrobial agents are the most common causes of nephrotoxic acute renal failure. In terms of prevention, avoiding nephrotoxins when possible is certainly desirable; fluid therapy is an effective prevention measure in certain clinical circumstances. Supporting cardiac output, mean arterial pressure, and renal perfusion pressure are indicated to reduce the risk for acute renal failure. Nonionic, isoosmolar intravenous contrast should be used in high-risk patients. Although urine output and serum creatinine lack sensitivity and specificity in acute renal failure, they remain the most used parameters in clinical practice.

SUMMARY

There are identified risk factors of acute renal failure. Because acute renal failure is associated with a worsening outcome, particularly if occurring in critical illness and if severe enough to require renal replacement therapy, preventive measures should be part of appropriate management.

Follow-up of patients with contrast-induced nephropathy

In this chapter, we review the approach to following the patient after contrast is administered. We first discuss the clinical importance of renal injury for if there were no clinically significant consequences of this renal injury, we would have far less concern for the adequacy of follow-up. We next look at markers of renal injury and what tests are used in clinical practice to define contrast-induced nephropathy (CIN). Finally, we discuss the steps that should be taken in those who do develop CIN to limit the impact of the injury and protect them from future adverse events.

Dynamics of mobilization and homing of endothelial progenitor cells after acute renal ischemia: modulation by ischemic preconditioning

Endothelial progenitor cells (EPCs) have been shown to participate in tissue repair under diverse physiological and pathological conditions. It is unknown whether EPCs are mobilized in response to acute renal injury. The aim of this study was to characterize EPC mobilization and homing in the course of acute renal ischemia. Mice were subjected to unilateral renal artery clamping (UC) for 25 min. At 10 min, 3, 6, 24 h, and 7 days after UC, the pool of circulating and splenic CD34+/Flk-1+ cells within the monocytic population was detected by flow cytometry. For ischemic preconditioning (IPC), the first UC was performed 7 days before the repeated ischemic episode. For EPC detection in the kidney, cryosections were stained for c-Kit+/Tie-2+ cells. The number of circulating EPCs was not significantly affected at any time after UC compared with sham-operated or control mice. IPC did not significantly change the circulating pool of EPCs. Splenectomy performed before UC resulted in a surge of circulating EPCs. Accordingly, splenic EPCs were significantly increased after UC at 3 and 6 h, but not at later times. EPC homing to the spleen was absent in IPC animals. Immunohistochemical analysis of the kidneys showed a sixfold increase in the number of c-Kit+/Tie-2+ cells localized in the medullopapillary region in mice by day 7 after ischemia. Enriched population of c-Kit+/Tie-2+ cells from the medullopapillary parenchyma of Tie-2green fluorescent protein chimeric mice subjected to IPC was isolated and transplanted to wild-type mice with acute renal ischemia. This procedure resulted in the improvement of renal function in recipients. In conclusion, 1) renal ischemia rapidly (within 3-6 h) mobilizes EPCs, which transiently home to the spleen, acting as a temporary reservoir of mobilized EPCs; 2) the late phase of IPC is associated with the mobilization of the splenic pool and accumulation of EPCs in the renal medullopapillary region; and 3) transplantation of EPC-enriched cells from the medullopapillary parenchyma afforded partial renoprotection after renal ischemia, suggesting the role of the recruited EPCs in the functional rescue.

Year in review: Critical Care 2004 - nephrology

We summarize all original research in the field of critical care nephrology published in 2004 or accepted for publication in Critical Care and, when considered relevant or directly linked to this research, in other journals. Articles were grouped into four categories to facilitate a rapid overview. First, regarding the definition of acute renal failure (ARF), the RIFLE criteria (risk, injury, failure, loss, ESKD [end-stage kidney disease]) for diagnosis of ARF were defined by the Acute Dialysis Quality Initiative workgroup and applied in clinical practice by some authors. The second category is acid-base disorders in ARF; the Stewart-Figge quantitative approach to acidosis in critically ill patients has been utilized by two groups of researchers, with similar results but different conclusions. In the third category - blood markers during ARF - cystatin C as an early marker of ARF and procalcitonin as a sepsis marker during continuous venovenous haemofiltration were examined. Finally, in the extracorporeal treatment of ARF, the ability of two types of high cutoff haemofilters to influence blood levels of middle- and high-molecular-weight toxins showed promise.

Urine IL-18 is an early diagnostic marker for acute kidney injury and predicts mortality in the intensive care unit

Serum creatinine is not an ideal marker of renal function in patients with acute kidney injury (AKI). Previous studies demonstrated that urinary IL-18 is increased in human AKI. Thus, whether urine IL-18 is an early diagnostic marker of AKI was investigated. A nested case-control study was performed within the Acute Respiratory Distress Syndrome (ARDS) Network trial. AKI was defined as an increase in serum creatinine by at least 50% within the first 6 d of ARDS study enrollment. A total of 400 urine specimens that were collected on study days 0, 1, and 3 of the ARDS trial were available from 52 case patients and 86 control patients. The data were analyzed in a cross-sectional manner and according to the time before development of AKI. The median urine IL-18 levels were significantly different at 24 and 48 h before AKI in case patients as compared with control patients. On multivariable analysis, urine IL-18 values predicted development of AKI 24 and 48 h later after adjustment for demographics, sepsis, Acute Physiologic Assessment and Chronic Health Evaluation (APACHE) III score, serum creatinine, and urine output. Urine IL-18 levels of >100 pg/ml are associated with increased odds of AKI of 6.5 (95% confidence interval 2.1 to 20.4) in the next 24 h. On diagnostic performance testing, urine IL-18 demonstrates an area under the receiver operating characteristic curve of 73% to predict AKI in the next 24 h. The urine IL-18 values were also significantly different between survivors and nonsurvivors (P < 0.05), and on multivariable analysis, the urine IL-18 value on day 0 is an independent predictor of mortality. Urinary IL-18 levels can be used for the early diagnosis of AKI. Urine IL-18 levels also predict the mortality of patients who have ARDS and are in the intensive care unit.

Early prediction of acute renal injury using urinary proteomics

AIMS

The lack of early biomarkers for acute renal failure (ARF) has crippled our ability to launch potentially effective therapeutic measures. We tested the hypothesis that urinary proteomics could identify novel early biomarker patterns for ischemic renal injury.

METHODS

Sixty patients undergoing cardiopulmonary bypass (CPB) were enrolled. Urine samples obtained at 2 and 6 h post CPB were analyzed by Surface-Enhanced Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SELDI-TOF-MS). The primary outcome variable was ARF, defined as a 50% or greater increase in serum creatinine.

RESULTS

Fifteen patients (25%) developed ARF 2-3 days after CPB. SELDI-TOF-MS analysis of urine from the ARF group at baseline versus at 2 and 6 h post-CPB consistently showed a marked and statistically significant enhancement of protein biomarkers with m/z of 6.4, 28.5, 43 and 66 kDa. The same biomarkers were enhanced when comparing control versus ARF groups at 2 and 6 h post-CPB. The sensitivity and specificity of the 28.5-, 43- and 66-kDa biomarkers for the prediction of ARF at 2 h following CPB was 100%. The receiver operating characteristic curves revealed an area under the curve of 0.98.

CONCLUSION

SELDI-TOF-MS is a novel, non-invasive, sensitive, highly predictive, reproducible, rapid method for the prediction of acute renal injury following CPB.

Neutrophil gelatinase-associated lipocalin (NGAL) as a biomarker for acute renal injury after cardiac surgery

BACKGROUND

The scarcity of early biomarkers for acute renal failure has hindered our ability to launch preventive and therapeutic measures for this disorder in a timely manner. We tested the hypothesis that neutrophil gelatinase-associated lipocalin (NGAL) is an early biomarker for ischaemic renal injury after cardiopulmonary bypass.

METHODS

We studied 71 children undergoing cardiopulmonary bypass. Serial urine and blood samples were analysed by western blots and ELISA for NGAL expression. The primary outcome measure was acute renal injury, defined as a 50% increase in serum creatinine from baseline.

FINDINGS

20 children (28%) developed acute renal injury, but diagnosis with serum creatinine was only possible 1-3 days after cardiopulmonary bypass. By contrast, urine concentrations of NGAL rose from a mean of 1.6 microg/L (SE 0.3) at baseline to 147 microg/L (23) 2 h after cardiopulmonary bypass, and the amount in serum increased from a mean of 3.2 microg/L (SE 0.5) at baseline to 61 microg/L (10) 2 h after the procedure. Univariate analysis showed a significant correlation between acute renal injury and the following: urine and serum concentrations of NGAL at 2 h, and cardiopulmonary bypass time. By multivariate analysis, the amount of NGAL in urine at 2 h after cardiopulmonary bypass was the most powerful independent predictor of acute renal injury. For concentration in urine of NGAL at 2 h, the area under the receiver-operating characteristic curve was 0.998, sensitivity was 1.00, and specificity was 0.98 for a cutoff value of 50 microg/L.

INTERPRETATION

Concentrations in urine and serum of NGAL represent sensitive, specific, and highly predictive early biomarkers for acute renal injury after cardiac surgery.