Background: Accurate glomerular filtration rate (GFR) evaluation is significant for drug dosing of carboplatin, anticancer drug excreted mainly from kidney. Serum cystatin-C (sCys-C) is a GFR marker with little affected by body muscle mass volume. And GFR equations based on serum creatinine (eGFRcreat) and sCys-C (eGFRcys) were developed; however, accuracy of eGFRcys has not been elucidated fully among patients with cancer. Therefore, we analyzed the performance of GFR equations among patients with cancer whose GFR values were measured by inulin clearance (Cin). Methods: Study design was a cross-sectional study. Subjects were 41 patients with cancer whose GFR values were measured by Cin for drug dosing studies of carboplatin or S-1 in Nagoya University Hospital from 2007 to 2010 and 29 non-cancer patients. Correlation with Cin and slope of regression line were evaluated in eGFRcreat and eGFRcys. Single and multiple regression analyses were analyzed to identify associating factors with eGFRcreat/Cin or eGFRcys/Cin. Results: Age, body weight, body mass index (BMI) and sCr were different between cancer patients and non-cancer patients, but sCys-C and Cin were consistent in 2 groups. The slope of the regression line for Cin vs. eGFRcys with zero intercept in cancer patients was 1.10 (95 % CI: 1.02–1.17), which was significantly different from 1.0. In multiple regression analysis revealed that BMI and urinary creatinine excretion were significantly associated with eGFRcreat/Cin, and cancer was only associating factor with eGFRcys/Cin. Conclusion: eGFRcys should not be used for evaluation of renal function in patients with cancer because it underestimates GFR.
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