Original Article A Modified Algorithm of the Single Pool Urea Kinetic Model

Abstract. Urea Kt/V, calculated according to the variable volume single pool urea kinetic model (UKM), has been accepted as the yardstick reflecting the adequacy of haemodialysis therapy. However, the classical algorithm of UKM requires great care in dialyser urea clearance (K) measurement in order to avoid major inaccuracies in esti-mating the urea distribution volume (V). Thus, we suggest a modified algorithm of UKM which avoids the measure-ment of K. It assumes an arbitrary V value and then calcu-lates kinetically K as a function of the assumed V value. The rationale of the modified algorithm can be derived from the knowledge that the classical algorithm imposes a proportionality ratio between K and V: given a particular set of data, a change in the attributed value of K leads to a proportional change in the calculated V value, so that the ratio K/V remains nearly constant. Aims of the study were (1) to validate the modified algorithm by comparing the resulting Kt/V and norma-lised protein catabolic rate (NPCR) values with the hom-ologous ones obtained using the classical algorithm in a group of 33 patients on thrice-weekly haemodialysis; plasma water urea concentrations were used with the classical algorithm (CApw) and the modified algorithm (MApw); and (2) to verify the possibility of using plasma urea concentrations with the modified algorithm (MAp) instead of the more rigorous plasma water concentrations. NPCR (g/kg per day) was 1.33 ±0.05 in CApw, 1.29 ±0.05 in MApw and 1.28 ±0.04 in MAp. Kt/V was 1.27 ± 0.03 in CApw, 1.25 ± 0.03 in MApw and 1.26 ± 0.03 in MAp. Statistical analysis showed no significant differ-ence and an excellent correlation (r = 0.98) of MApw and MAp vs CApw data. Correspondence and offprint requests to: Dr Francesco Casino MD