CST3 and chronic kidney disease: In accordance with previous results (20), creatinine production impairment may be responsible for significant creatinine GFR overestimation with respect to values predicted from cystatin C. The aim of our study was to investigate, in patients with different pathophysiological conditions, the impact of creatinine production on the agreement between GFR estimates from serum cystatin C and creatinine using the 4- and 6-variable Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations.