DESPITE numerous studies dealing with various aspects of the renal concentrating mechanism,1-18 relatively little data are available concerning normal concentrating capacity in infants and children.
In recent years it has been demonstrated, in human beings7,8,15,18 as well as in a variety of experimental animals, that a major factor influencing concentrating performance in response to dehydration is the dietary intake of protein prior to the study. This source of variation has not been taken into account in studies of so-called normal urinary concentrating capacity. Although most tests of concentrating performance have followed a period of 16 to 24 hours of fluid deprivation, this procedure is difficult to do in small children and may be hazardous. Finally, although concentrating performance is regarded as a good index of overall functional status1 of the kidney, no systematic investigation of its relation to other tests of kidney function in infants and children