Effects of serum albumin and glycated albumin levels on performance of the Japanese GFR equation based on serum cystatin C

Background: We reported that both serum albumin (Alb) and glycated albumin (GA) levels influenced the performance of the Japanese GFR equation based on serum creatinine. In the present study, we studied the effects of both markers on the estimated GFR by Japanese GFR equation based on serum cystatin C (Eq-cys). Methods: 715 Japanese subjects were included. GFR was measured by inulin renal clearance (Cin). Correlations between estimated GFR by Eq-cys (eGFRcys) and Cin were evaluated in subjects stratified by GA (GA-1: GA ≤ 16.3 % and GA-2: GA ≥ 16.4 %) and Alb levels (Alb-1: Alb ≤ 3.5 g/dl and Alb-2: Alb ≥ 3.6 g/dl). Results: Correlation coefficients between eGFRcys and Cin were 0.863, 0.919, 0.948 and 0.974 in GA-1, GA-2, Alb-1 and Alb-2, respectively. Slopes (95 % confidential interval) of the regression lines with zero intercepts were 1.014 (0.993–1.035), 0.989 (0.944–1.033), 1.019 (0.970–1.068) and 1.011 (0.990–1.031), respectively. The slopes were not significantly different from 1.0, suggesting that Eq-cys performed well in subjects at wide spectrum of GA and Alb levels. Single regression analysis of GA on eGFRcys/GFR was not significant in total subjects and subjects with GA > 12.4 %. Single regression analysis of Alb on eGFRcys/GFR was significant in total subjects, but the correlation coefficient was very low (r = 0.08, p = 0.03). Multiple regression analysis showed that Alb and GA were not significantly associated with eGFRcys/Cin in subjects with GA > 12.4 %. These results suggested that both parameters were not important factors affecting the performance of Eq-cys. Conclusion: Performance of Eq-cys was well irrespective of GA and Alb levels. Both parameters were not important factors affecting the estimated GFR by Eq-cys.