Factors affecting renal hydrogen ion excretion capacity in healthy children.

In 560 healthy German children and adolescents aged 2.8-22.0 years from the DONALD (Dortmund Nutritional and Anthropometric Longitudinally Designed) study, the relationship between urine pH and renal net acid excretion (mmol/day/1.73 m2) was analysed. A quadratic model showed the best fit (r2 = 0.608). Using logistic regression analysis three parameters (urinary phosphorus excretion, total protein intake and urinary ratio of potassium and sodium) had a significant effect on renal hydrogen ion excretion capacity characterised by the probability of high or low net acid excretion with respect to the urine pH value. Urinary osmolality, in contrast to what has been seen in a previous experimental study with low birth weight infants, along with sex and age had no significant independent effects on renal net acid excretion with respect to the urine pH value over the range of osmolalities observed. In healthy children and adolescents a low fluid intake with high urinary osmolality does not at least substantially decrease the renal capacity of hydrogen ion excretion.