Total body nitrogen as a prognostic marker in maintenance dialysis

In order to assess long-term nutritional adequacy, 154 patients on maintenance dialysis (78 on hemodialysis (HD), 76 on continuous ambulatory peritoneal dialysis (CAPD)) underwent measurement of total body nitrogen (TBN) with concurrent recording of dietary history, anthropometrics, and serum albumin. Seventy-one patients were reassessed 23.3 +/- 2.2 (5 to 76) months later. In cross-sectional analyses, anthropometric measurements and dietary intake remained stable over time in all patients. However, a significant fall in TBN occurred in the HD population with increasing time on dialysis (P < 0.05). In the prospective analyses, CAPD patients (N = 26) had a significant increase in TBN (P < 0.02). In contrast, longitudinal measurements of TBN in HD patients (N = 36) tended to fall but did not reach significance (P = 0.18). TBN correlated with total caloric intake estimated from the dietary history (P < 0.05), but not with estimated protein intake. During follow-up, 38 patients died. These patients were older (P < 0.05), and in the CAPD population, they had been on dialysis for a longer time (P < 0.05). Those who died had a lower TBN expressed both as grams per kilogram lean body mass (P < 0.005) and as the nitrogen index (P < 0.05). The probability of death within 12 months in the patients with a nitrogen index (ratio of the measured nitrogen to the predicted nitrogen for a sex-, age-, and height-matched control) less than 80% of the predicted normal value was 48%. The relative risk of death in this population was 4.1.