A simple approach for assessing equilibrated Kt/V 2-M on a routine basis

Background. Large observational studies have shown a reduction in morbidity and mortality in patients on high-flux haemodialysis (HD) or convective techniques, compared with low-flux HD. An index to evaluate treatment efficiency in middle molecule (MM) removal would be recommended. Since beta-2-microglobulin (beta 2-M) is a recognized MM marker, we evaluated an easy approach for Kt/V beta 2-M assessment on a routine basis, avoiding other complex methods. Methods. An equation that estimates single-pool (sp) Kt/V beta 2-M was derived from Leypoldt's formula, which calculates beta 2-M dialyser clearance (Kt/V beta 2-M) from the post/pre-dialysis beta 2-M concentration (C-t/C-0) ratio and the weight loss/ end-dialysis weight (Delta W/W) ratio. Our equation, spKt/ 1/1.,24m = 6.12 A W/W [1 ln(C-t/C-0)/In(1 + 6.12 W/W)], was derived by assuming urea distribution volume (V) as 49% of Wand beta 2-M volume (Kt/V beta 2-M) as V-u/3, in agreement with the average patient values in the HEMO Study. The spKt/V beta 2-M values calculated with our equation (F) in 129 patients on 407 sessions of different high-flux treatments were compared with those calculated with the method applied in the HEMO Study (HM). Equilibrated beta 2-M concentration (C-eq) of the same sessions was also estimated with the equation for C'eq by Tattersall, and equilibrated Kt/V beta 2-M was calculated by introducing Tattersall's equation into our simplified spKt/V beta 2-M formula. Results. Mean results of our spKt/V beta 2-M equation (F) were very close to those of the HM method (1.48 +/- 0.38 vs 1.47 +/- 0.37). The difference was less than +0.1 in 95% of cases. A mean end-session beta 2-M rebound of 44 +/- 14% was predicted, which caused a mean reduction in actual Kt/V(beta 2-M)of similar to 27% (eKt/V beta 2-M = 1.08 +/- 0.26). Conclusions. The method proposed to estimate spKt/VN_m and eKt/V beta 2-M could become a simple tool to monitor the efficiency of high-flux HD and convective techniques and to evaluate the adequacy of treatments in terms of MM removal. Moreover, it might help to better understand the effects of different dialysis schedules. Validation on a larger dialysis population is required.