Comparison of serum cystatin C and creatinine changes after cardiopulmonary bypass in patients with normal preoperative kidney function

Serum creatinine is used ubiquitously to estimate glomerular filtration rate and to diagnose acute kidney injury after cardiac surgery. Serum cystatin C is a novel biomarker that has emerged as a possible diagnostic alternative to serum creatinine. It is unclear if the dynamic changes in serum cystatin C immediately following cardiopulmonary bypass (CPB) differ from those of serum creatinine in patients with normal preoperative kidney function. We compared changes in serum levels of creatinine and cystatin C by measuring them serially in 19 patients undergoing CPB. Within-patient differences for serum creatinine and serum cystatin C were compared by repeated measures ANOVA. Serum creatinine and cystatin C levels showed significant correlation with each other. Both biomarkers showed a significant decrease after CPB, but their serum concentrations reverted to pre-CPB levels within 12 h. Serum levels of serum creatinine remained unchanged from baseline levels throughout 72-h post-CPB. In contrast, serum cystatin C levels rose further and became significantly higher compared to baseline within 48 h. Serum cystatin C remained significantly elevated at 48- and 72-h post-CPB. Processes that determine the serum concentrations of serum creatinine and cystatin C in the post-CPB period affect the two biomarkers differently, suggesting that the two are not interchangeable as diagnostic markers of glomerular filtration rate. Future studies are needed to examine if these discrepancies are related to differences in their production rates, in their ability to detect small changes in glomerular filtration rate, or to a combination of these, and to determine the effect of such differences on the diagnostic and prognostic accuracy of the two biomarkers.