Validation of formulas calculating normalized protein catabolic rate in patients undergoing home hemodialysis.

Depner and Daugirdas developed a simplified formula to estimate the normalized protein catabolic rate in patients on twice- or thrice-weekly hemodialysis (JASN, 1996). The aim of our work was to establish formulas in more frequent schedules and validate them in home-based hemodialysis patients. We realized that the structure of Depner and Daugirdas' normalized protein catabolic rate formulas has a general meaning and can be expressed as PCRn = C0/[a + b*(Kt/V) + c/(Kt/V)] + d, where C0 is pre-dialysis blood urea nitrogen, Kt/V is dialysis dose, a, b, c, d are the specific coefficients for each combination of home-based hemodialysis schedules and the day of blood sampling. The same applies to the formula that adjusts C0 (C'0) for residual kidney clearance of blood water urea (Kru) and urea distribution volume (V): C'0 = C0*[1 + (a1 + b1/(Kt/V))*Kru/V]. On this basis, we computed the six coefficients (a, b, c, d, a1, b1) for each of the 50 possible combinations and simulated a total of 24,000 weekly dialysis cycles using the Daugirdas Solute Solver software recommended by the KDOQI 2015 guidelines. From the associated statistical analyses we obtained 50 sets of coefficient values, which were validated comparing the paired normalized protein catabolic rate values (i.e., those estimated with our formulas with those modeled with Solute Solver) in 210 datasets of 27 patients on home-based hemodialysis. The mean values ± SD were 1.06 ± 0.262 and 1.07 ± 0.283 g/kg/day, respectively, with a mean difference of 0.004 ± 0.034 g/kg/day (p = 0.11). The paired values were highly correlated (R2 = 0.99). In conclusion, even if the coefficient values were validated in a relatively small sample of patients, they allow an accurate estimation of normalized protein catabolic rate in home-based hemodialysis patients.