Dietary protein, urea nitrogen appearance and total nitrogen appearance in chronic renal failure and CAPD patients.

This study was carried out to examine the mathematical relationships between the urea nitrogen appearance (UNA), total nitrogen appearance (TNA) and dietary nitrogen intake (DNI) in patients with chronic renal failure. Studies were conducted in 20 nondialyzed patients with advanced chronic renal failure (CRF) who were fed 27 constant protein diets for 24.8 +/- 9.5 days (SD) and eight patients undergoing continuous ambulatory peritoneal dialysis (CAPD), who ingested 13 constant protein diets for 20.3 +/- 4.9 days. All patients lived in a hospital research ward throughout the study and underwent full nitrogen balance measurements. Data were analyzed after patients attained equilibrium or near equilibrium with each dietary protein intake. In the CRF patients, using the mean values obtained during the equilibrium phase, there was a direct and precise correlation between the TNA and UNA, where TNA g/day = 1.19 UNA g/day + 1.27 g/day, r = 0.948. The correlation between DNI and UNA was also highly significant, but less precise, with somewhat greater 95% confidence intervals: DNI g/day = 1.20 UNA g/day + 1.74 g/day, r = 0.865. The relationship between DNI and TNA was not much more precise: DNI g/day = 0.97 TNA g/day + 0.65 g/day, r = 0.880. With the CAPD patients, the relationships were as follows: TNA g/day = 0.94 UNA g/day + 5.54 g/day, r = 0.956; DNI g/day = 0.97 UNA g/day + 6.80 g/day, r = 0.705; DNI g/day = 1.07 TNA g/day + 0.63 g/day, r = 0.760. For the CAPD patients, the lowest 95% confidence intervals were also found for the correlation between TNA and UNA. Thus, in both CRF and CAPD patients, the TNA is highly and precisely correlated with the UNA. The DNI is also significantly correlated with UNA and TNA, but the relationship is less precise. In both of these two groups of patients, the difference between the regression equations for TNA versus UNA and DNI versus UNA was, to a substantial degree, accounted for by the intercept.