PROTEIN NITROGEN APPEARANCE IN CAPD PATIENTS - WHAT IS THE BEST FORMULA

Background. The protein equivalent of nitrogen appearance: is an indir ect index commonly used to assess dietary protein intake in patients o n CAPD. Moreover it has been suggested that the ratio between nitrogen appearance and dietary nitrogen intake (fractional urea synthesis) ca n predict nitrogen balance in uraemic patients. Several formulae to di rectly calculate the protein equivalent of nitrogen appearance have be en published, It has not been established, however, what formulae give the most appropriate estimate of protein intake and nitrogen appearan ce, Study design. Nitrogen balance studies were carried out in seven s table patients on CAPD, All of the patients were receiving a diet whos e protein content (1.2 g/kg/body wt/day) and calorie content (35 kcal/ kg/body wt/day) were rigorously controlled. Sis formulae for calculati ng protein equivalent of nitrogen appearance and nitrogen appearance w ere 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 +/- 0.9 g/N day, protein intake (g/day) 81 +/- 19, protein in take (g/kg) 1.05 +/- 0.17. Differences in protein equivalent of nitrog en appearance of up to about 20% were found, The smallest differences between protein equivalent of nitrogen appearance and protein intake w ere obtained by the formulae or Bergstrom (1 +/- 7 g, limits of agreem ent -12 and +15 g) and Blumenkrantz (-2 +/- 5 g) limits of agreement - 11 and +7 g), The formula of Bergstrom most closely estimated nitrogen appearance (-0.35 +/- 0.89 g). Using such formula, the fractional ure a synthesis was 54 +/- 12%, giving evidence of positive nitrogen balan ces. Conclusion, For the routine monitoring of protein equivalent of n itrogen appearance in CAPD patients, we recommend Bergstrom's formula with the determination of dialysate protein losses.