Changes in serum cystatin C, creatinine, and C‐reactive protein after cardiopulmonary bypass in patients with normal preoperative kidney function

Abstract Aim The use of cardiopulmonary bypass (CPB) can cause changes in serum creatinine and cystatin C independent of glomerular filtration rate. We aimed to quantify the temporal changes of these biomarkers and C‐reactive protein (CRP) after CPB. Methods This was a prospective study at an academic medical centre between April and October 2013. We compared postoperative changes in serum creatinine and cystatin C in 38 patients with normal preoperative kidney function who underwent cardiac surgery using CPB and did not develop perioperative acute kidney injury (AKI). The effect of inflammation on intra‐individual changes was examined in mixed effects regressions, using measurements of pre‐ and postoperative CRP. Results Both serum creatinine (79.9 ± 22.7 vs. 92.6 ± 21.4 µmol/L, P = 0.001) and cystatin C (1.16 ± 0.39 vs. 1.33 ± 0.37 mg/L, P = 0.012) decreased significantly in the first 8 h postoperatively compared to preoperatively, as a result of haemodilution. Thereafter serum creatinine returned to preoperative levels, whereas serum cystatin C continued to rise and was significantly elevated at 72 h post‐CPB compared to preoperative levels (1.53 ± 0.48 vs. 1.33 ± 0.37 mg/L, P = 0.003). CRP levels increased significantly post‐CPB and were significantly associated with increases in both serum creatinine and cystatin C. Conclusion Serum creatinine and cystatin C appear not to be interchangeable biomarkers during and immediately after CPB. Processes unrelated to kidney function such as acute inflammation have a significant effect on post‐CPB changes in these biomarkers, and may result in significant increases in serum cystatin C that could erroneously be interpreted as AKI.