The post: pre dialysis plasma urea nitrogen ratio to estimate K.t/V and NPCR: validation

Abstract

The ability of empirical formulae to predict K.t/V based on the ratio (R) of the postdialysis (Ct) to predialysis (Co) plasma urea nitrogen levels was tested. In 256 patients, 336 three-point modeling sessions were performed. The K.t/V and NPCR were derived by interative solution of equations for V and G according to the variable volume single-pool model. The modeled K.t/V values were compared to K.t/V predicted from the formula: K.t/V = -ln (R - 0.008.t-UF/W), where R is the Ct/Co ratio, t the session length (h), UF the ultrafiltrate volume (liters) and W the postdialysis weight (kg). Further, the ratio-derived K.t/V was used in conjunction with the Gotch nomogram for 3/week dialysis to estimate NPCR (NPCR-R/N); the latter value was compared to the NPCR from standard 3-point modeling (NPCR-MOD). The two K.t/V values were quite similar, although statistically separable: modeled K.t/V, 0.97 +/- 0.22 (SD), ratio-derived K.t/V 0.96 +/- 0.23, p less than 0.001. The mean percent error was -0.73% +/- 2.5 (range - 11 to + 4.8), and the correlation coefficient was 0.994, slope 1.01, int -0.016. Modifications of the prediction formula which incorporated UF/V instead of UF/W, and/or which weighted the UF/V term according to the expected K.t/V, produced only slight improvement in accuracy. The two values of NPCR were less similar, but still highly correlated: NPCR-MOD, 1.04 +/- 0.26 g/kg/day, NPCR-R/N, 0.94 +/- 0.23, p less than 0.001; mean percent error, - 8.2 +/- 16; r = 0.78, slope = 0.68, int = 0.23.(ABSTRACT TRUNCATED AT 250 WORDS)