EVALUATION OF PROTEIN-INTAKE BY DIETARY DIARIES AND UREA-N EXCRETION IN CHILDREN WITH CHRONIC-RENAL-FAILURE

In 1988 a European multicentre, randomized trial was started in order to analyse the influence of protein intake on the progression of chron ic renal failure in children. Compliance to the dietary prescriptions, i. e. protein intake, was checked by written dietary diaries and in a ddition by urinary urea-N excretion. This provided a unique chance to compare both methods in non-hospitalized children. Of total of 200 pat ients 123 were selected, in whom at least 4 consecutive dietary diarie s plus 4 completely collected 24-hour urine samples were available. Wh ereas urea-N excretion and simultaneously recorded protein intake did not correlate well, mean urinary urea-N excretion and mean protein int ake of at least 4 observations in each patient correlated highly (r = 0.803, p = 0.0001). The difference between protein-N intake and urea-N excretion was not a constant amount of 0.031 g/kg/day as proposed by Maroni et al. [1985] but figured at 0.085 +/- 0.061 g/kg/day and was h ighly correlated to protein intake (r = 0.839, p = 0.0001). The correl ation of protein intake and urea-N excretion was best described by the formula: protein-intake (g/kg/day) = (urea-N excretion [g/kg/day] x 1 5.39) -0.8 or protein intake (g/kg/day) = urea-N excretion (g/kg/day) x 9.5. Maroni's formula underestimated the high protein intake of youn g children. In only a few patients dietary diaries severely underestim ated protein intake as compared to calculation by urea-N excretion. Bu t, analysing the plausibility of declaration of energy intake by check ing weight gain and the coefficient of variation of individual protein intake and urea-N excretion it seemed to be most likely that in these children urea-N excretion better reflected protein intake than dietar y diaries. In summary, if written diaries are not available, calculati on of mean urea-N excretion from at least four consecutive measurement s during an adequate period of time is a valuable tool to estimate pro tein intake in children, provided the patients don't suffer from calor ic malnutrition or severe acidosis.