Dialysis

Abstract Background. The protein equivalent of nitrogen appearance is an indirect index commonly used to assess dietary protein intake in patients on CAPD. Moreover it has been suggested that the ratio between nitrogen appearance and dietary nitrogen intake (fractional urea synthesis) can predict nitrogen balance in uraemic patients. Several formulae to dir-ectly calculate the protein equivalent of nitrogen appearance have been published. It has not been established, however, what formulae give the most appropriate estimate of protein intake and nitrogen appearance. Study design. Nitrogen balance studies were carried out in seven stable patients on CAPD. All of the patients were receiving a diet whose protein con-tent (1.2 g/kg/body wt/day) and calorie content (35 kcal/kg/body wt/day) were rigorously controlled. Six formulae for calculating protein equivalent of nitrogen appearance and nitrogen appearance were tested and the agreement of the estimating formulae was evaluated by means of the Bland and Altman method. Result. Net nitrogen balance was 1.68±0.9g/N day, protein intake (g/day) 81 + 19, protein intake (g/kg) 1.05 + 0.17. Differences in protein equivalent of nitrogen appearance of up to about 20 % were found. The smallest differences between protein equi-valent of nitrogen appearance and protein intake were obtained by the formulae of Bergstrom (1 + 7 g, limits of agreement —12 and +15g) and Blumenkrantz (—2±5g, limits of agreement —11 and +7g). The formula of Bergstrom most closely estimated nitrogen appearance (—0.35 + 0.89 g). Using such formula, the fractional urea synthesis was 54+ 12%, giving evidence of positive nitrogen balances. Conclusion. For the routine monitoring of protein equivalent of nitrogen appearance in CAPD patients, we recommend Bergstrom's formula with the deter-mination of dialysate protein losses. Key words: PNA; protein intake; nitrogen balance