CST4 and chronic kidney disease: In a comparison of the correlation coefficients we found that the correlations between 51CrEDTA clearance and the simple cystatin C formula and 51CrEDTA clearance and the MDRD formula or the CKD-EPI formula and 51CrEDTA clearance were superior to the correlation between 51CrEDTA clearance and the C&G formula (P = 0.034 for the simple cystatin C formula, P = 0.0048 for the CKD-EPI formula, P = 0.0001 for the CKD-EPI creatinine and cystatin formula and P = 0.0038 for the MDRD formula).