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 chronic renal failure in children. Compliance to the dietary prescriptions, i. e. protein intake, was checked by written dietary diaries and in addition by urinary urea-N excretion. This provided a unique chance to compare both methods in non-hospitalized children. Of total of 200 patients 123 were selected, in whom at least 4 consecutive dietary diaries plus 4 completely collected 24-hour urine samples were available. Whereas urea-N excretion and simultaneously recorded protein intake did not correlate well, mean urinary urea-N excretion and mean protein intake 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 highly correlated to protein intake (r = 0.839, p = 0.0001). The correlation 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 15.39) -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 young children. In only a few patients dietary diaries severely underestimated protein intake as compared to calculation by urea-N excretion. But, analysing the plausibility of declaration of energy intake by checking 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 dietary diaries. In summary, if written diaries are not available, calculation of mean urea-N excretion from at least four consecutive measurements during an adequate period of time is a valuable tool to estimate protein intake in children, provided the patients don't suffer from caloric malnutrition or severe acidosis.