Factors influencing glomerular filtration rate as estimated using preoperative creatinine and cystatin C levels.

Objectives: Estimated glomerular filtration rate (eGFR) using serum creatinine (Cr) is commonly used to evaluate renal function. However, it can be influenced by other factors, which can risk the overestimation of the true GFR. Impaired renal function prior to cardiovascular surgery reportedly increases mortality and the incidence of postoperative complications. Thus, overestimation of renal function may affect the assessment of postoperative complication risks. Therefore, we aimed to compare the eGFR calculated from serum Cr and cystatin C (Cys-C) levels to assess preoperative renal function and to investigate factors affecting renal function overestimation.

Materials and methods: 88 patients admitted for cardiovascular surgery who had preoperative serum Cr and Cys-C measurements were included in the study. Correlations between factors associated with eGFR calculated from serum Cr (eGFRcre) and Cys-C (eGFRcys) and their ratio (eGFRcre/eGFRcys) were examined using multiple regression analysis.

Results: Multiple regression analysis revealed that eGFRcre/eGFRcys was significantly negatively correlated with the Short Physical Performance Battery score (SPPB). A clinically significant difference in renal function overestimation was defined as GFRcre/eGFRcys > 1.2, with a cutoff value of 9 points for the SPPB score. The chair stand test, a component of the SPPB, had the same discriminative power as the SPPB for identification of renal function overestimation.

Conclusion: The SPPB can be used to identify likely GFR overestimation in patients. Additionally, the chair stand test may be used as an alternative to the SPPB for the identification of renal function overestimation when the SPPB is difficult to perform.