CYSTATIN C AS A SURROGATE MARKER FOR EVALUATING GLOMERULAR FILTRATION RATE IN ACUTE KIDNEY INJURY

BACKGROUND The gold standard for measuring GFR has practical limitations in clinical practice; instead it is estimated by use of the serum concentration of endogenous filtration markers. The objective of this research was to compare serum cystatin C with serum creatinine for Estimating Glomerular Filtration Rate (eGFR) in acute kidney injury and to determine whether elevated serum cystatin C has an impact on mortality in the presence of kidney injury. METHODS This prospective observation study was carried out for 18 months in our institution. It included all indoor Acute Kidney Injury (AKI) patients more than 18 years, admitted in the Department of Medicine of our tertiary care centre. The renal function of the patients was evaluated by testing for serum creatinine and serum cystatin C. Serum creatinine based Cockcroft and Gault (CG) equation and Estimated GFR (e-GFR) with Modification of Diet in Renal Disease (MDRD) equation were compared with serum cystatin C based e-GFR Hoek and Larsson equations. All-cause mortality was ascertained by examination of death certificates, inpatient hospital records. RESULTS A total of 90 patients were enrolled during the study. The mean serum creatinine (mg/dL) 3.455+/-1.77, serum cystatin (mg/L) 2.932+/-1.13, and creatinine clearance (CG) 27.16+/-16.96, eGFR-MDRD (mL/min.) 24.94+/-17.95, eGFR-Larsson 31.60+/-17.36 and eGFR-Hoek 29.00+/-17.39. The correlation of the Larsson and Hoek cystatin C based GFR estimates (r=0.94; p=<0.001) and MDRD and CG serum creatinine based GFR estimates (r=-0.93; p<0.001) were highly significant. In multiple logistic regression analysis which included age, serum creatinine and serum cystatin C as variables, only serum cystatin C (p=0.046) was found to be a significant factor influencing mortality in acute kidney injury. CONCLUSIONS The present study suggests that the cystatin C-based prediction equation achieved a diagnostic performance that was at least as good as the creatinine based formulas. Serum cystatin C has superior diagnostic value than serum creatinine in influencing mortality in patients with acute kidney injury.