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

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.