Variation in measures of urea kinetics over four years in a single adult.

Urea kinetics was measured in a single woman on five occasions over four years by the prime/intermittent oral-dose method with [15N15N]-urea. On a nitrogen intake of 231 +/- 24 mg/kg/day, urea production was 198 +/- 22 mg/kg/day, with the urinary excretion of urea being 143 +/- 25 mg/kg/day. Urea hydrolysis and salvaging in the bowel was 55 +/- 6 mgN/kg/day. The coefficients of variation for production, 11 per cent, excretion, 18 per cent, and hydrolysis, 11 per cent, were similar to that for intake, 10 per cent, and substantially less than reported inter-individual variations from other studies. It is concluded that the method employed for measuring urea kinetics gives reproducible results and that the intra-individual variation in urea kinetics is much less than the inter-individual variation.