Relationship of renal threshold for bicarbonate reabsorption to urinary sodium excretion in premature infants.

Renal threshold for bicarbonate reabsorption and urinary sodium excretion of nine healthy male premature infants with a mean birth weight of 1734 g (range 1650-1900) was determined on the 7th day of life, and subsequently weekly for 6 consecutive weeks, by applying a repeated NH4Cl load. A close negative correlation was found between bicarbonate threshold and urinary sodium excretion (p less than 0.01). It is suggested that the limited renal capacity to reabsorb sodium may account for the low bicarbonate threshold in premature infants.