Use of the urine-to-blood carbon dioxide tension gradient as a measurement of impaired distal tubular hydrogen ion secretion among neonates

Abstract

To evaluate the utility of the urinary-minus-blood partial pressure of carbon dioxide (U-B P CO 2) gradient for the diagnosis of distal renal tubular acidosis in neonates, we measured the U-B P CO 2 gradient corresponding to different urinary bicarbonate concentrations in 40 neonates. The U-B P CO 2 gradient in these neonates had a significant linear relationship to the urinary bicarbonate concentration. When the urinary bicarbonate concentration was >10 mmol/L, in all the neonates the U-B P CO 2 could be increased above the 20 mm Hg level. We conclude that it is appropriate to determine the U-B P CO 2 gradient as an index of distal urinary acidification and that it is a necessary test for diagnosis of distal renal tubular acidosis in neonates. (J P EDIATR 1995;126:114-7)