New method to calculate creatinine generation rate using pre- and postdialysis creatinine concentrations.

The creatinine (Cr) generation rate reflects the muscle mass, a possible indicator of protein nutritional status. Thus, in this study, we developed equations for calculating the Cr generation rate. Depner and Daugirdas recently developed a method for determining the protein catabolic rate (PCR) from the pre- and postdialysis blood urea nitrogen concentrations. We modified their method to develop equations for calculating the total Cr generation rate from the measured predialysis Cr concentration and estimated postrebound concentration. The total Cr generation rate is defined as the sum of the intrinsic Cr generation rate and the extrinsic Cr generation rate (i.e., the generation rate of Cr derived from food). In the present study, the postrebound Cr concentration was estimated on the basis of postdialysis Cr concentration and the K/V for Cr. The intrinsic Cr generation rate was obtained by subtracting the extrinsic Cr generation rate, which was estimated on the basis of the PCR, from the total Cr generation rate calculated. The intrinsic Cr generation rate determined with this method was virtually the same as that obtained using the postrebound Cr concentration, the concentration immediately before the next hemodialysis (HD) session, and the PCR. The intrinsic Cr generation rate determined with the present method did not vary with changes in the HD prescription (i.e., with an increase in blood flow rate, a prolongation of the HD duration time, or a change in dialyzer membrane area). The present study also indicated that the intrinsic Cr generation rate decreased with age in both males and females.