The renal excretion of hydrogen ions in infants and children.

The ability of the kidneys to excrete an acid urine is often assessed by correlating plasma carbon dioxide and urine pH. A low plasma CO2 should be accompanied by a low urine pH, provided that respiratory function is normal. Buchanan and Komrower (1958) consider that the renal excretion of hydrogen ions is normal in children if urine pH falls below 5 0, after a single dose of 0g./kg. of ammonium chloride has been given to produce metabolic acidosis. Under similar conditions, urine pH falls to below 5 2 in normal adults (Wrong and Davies, 1959). However, Elkinton, Huth, Webster, and McCance (1960) found that urine pH was not suifficient to differentiate latent cases of renal tubular acidosis in adults after prolonged administration of NH4Cl. These authors suggested a quantitative assessment ofthe renal response to an ammonium chloride load by the 'hydrogen ion clearance index' calculated as the product of the total H+ excreted in the urine (mEq/min./l -73 sq. m.) and the plasma CO2 content (mEq/1.) in subjects after a continuous NH4Cl administration for 3-5 days. Abnormally low values of the index were considered to indicate renal acidosis. This index has not only proved a sensitive one in cases with latent renal tubular acidosis, but also useful in revealing the latent renal defect in otherwise normal relatives of patients with renal tubular acidosis, thus contributing to our knowledge of the genetics of the disease (Huth, Webster, and Elkinton, 1960). In the present study the renal H+ excretion on normal diet, as well as after the addition of NH4Cl for several days, has been investigated in order to determine values for the hydrogen ion clearance index in normal infants and children. Results from similar investigations in children with renal tubular acidosis and their relatives will be reported later.