OBJECTIVETo prospectively study the value of cystatin C in diagnosis of acute kidney injury (AKI) in patients after cardiac surgery.

METHODSA total of 132 patients undergoing cardiopulmonary bypass were enrolled in this prospectively study. From each patient, blood samples were collected everyday before and after operation to detect the serum creatinine (Scr) and cystatin C levels by enzymatic method and particle-enhanced turbidimetric immunoassay (PETIA), respectively, and the glomerular filtration rate (eGFR) was estimated using MDRD equation. AKI diagnosis was made according to the RIFLE criteria of the Acute Dialysis Quality Initiative (ADQI) (R: Scr increased by > or =50%; I: Scr increased by > or =100%; F: Scr increased by > or =200%; L: Loss of kidney function; E: End-stage renal disease). Another AKI diagnostic criterion was also adopted according to the levels of cystatin C increment, namely an increase by > or =50%, > or =100%, and > or =200%.

RESULTSTwenty-nine patients (21.9%) developed AKI of varied severities, including 10 meeting the R-criteria, 12 the I-criteria, 7 the F-criteria, with the other 103 patients without AKI serving as the control group. Cystatin C of the 29 AKI patients was drastically increased in comparison with that of the control group (P<0.001). Significant linear correlation was found between cystatin C and Scr (r=0.732, P<0.001) and between [cystatin C]-1 and estimated GFR (R=0.803, P<0.001). By the two diagnostic criteria based on cystatin C and Scr levels, respectively, the median diagnostic time of AKI was 2 days (range 1-4 days) and 3 days (range 2-5 days) for R criteria (10 patients, P=0.014), 3.5 days (range 1-6 days) and 5 days (range 2-8 days) for I criteria (12 patients, P=0.008), and 5 days (range 3-7 days) and 6.5 days (range 4-9 days) for F criteria (7 patients, P=0.02), respectively. ROC analysis confirmed excellent accuracy of cystatin C in AKI diagnosis (AUC=0.992). With the cut-off value of cystatin C increment by > or =50%, the diagnostic sensitivity and specificity of AKI was 92% and 95%, respectively.

CONCLUSIONCystatin C can serve as a good indicator for AKI diagnosis to allow earlier detection of AKI than Scr-based diagnosis in patients after cardiac surgery.