Comparison of two Methods for the Estimation of Urea Kinetics and Introduction of a Third Simplified Method

Abstract

It has been claimed that computed urea kinetic (UK) modelling in hemodialysed patients, for the estimation of protein intake, leads to an overestimation of protein catabolic rate (PCR). In the present study, three different methods of kinetic modelling for the determination of PCR and Kt/V are compared in 24 patients. The first method was the direct quantification method (DDQ) based on the collection of all urea eliminated from the body. The first computed method (ICMI) was the urea kinetic modelling method as described by Sargent. Dialyzer clearances were measured directly and not estimated by theoretical extrapolation. The second computed method (ICMII) is based on the indirect calculation of urea distribution volume (V_u), according to Watson, and of dialyzer clearances from this V_u and from pre- and post-dialysis urea concentrations. All three methods resulted in PCR's that were not significantly different (DDQ: 1.03 ± 0.19; ICMI: 1.04 ± 0.22; ICMII: 1.08 ± 0.25 mg/Kg BW.24 hrs; p > 0.05). When the results were correlated, the following results were obtained: ICMI vs ICMII: r = 0.89, p < 0.001; ICMI vs DDQ: r = 0.68, p < 0.01; DDQ vs ICMII: r = 0.78, p < 0.001. Intermutual comparison of Kt/V values resulted in virtually identical results, especially when comparing ICMI and ICMII, where the regression line equalled the identity line.

In conclusion, all methods seem equally reliable in determining mean PCR and Kt/V. Our data, obtained with directly measured dialyzer urea clearances, do not confirm the earlier held opinion that computed modelling results in an overstimation of PCR. The newly developed third method (ICMII) appears to be as equally reliable as the two other methods, but is easier to perform and less labour intensive.