Renal handling of phosphate in very low birthweight (VLBW) infants (less than 1.3 kg): effects of calcium and sodium intake.

Abstract

Five patient groups of VLBW infants with the same P-intake but varying Ca and Na intake were examined as to their urinary excretion of P and Na and on their renal clearance of P. The effect of increasing the Na intake from 1.5 to 3 mEq/kg/24 h on C(P) was also examined. In the control group of infants with an intake of 210 mg Ca and 80 mg P/kg/24 h, the C(P) was significantly correlated with postnatal, but not postconceptional age. A relatively low Ca intake of 100 mg/kg/24 h led to age-related values two to three times as high, whereas Ca supplementation to a total intake of 250 mg/kg/24 h decreased the C(P) significantly. A Ca intake of 175 mg/kg/24 h led to C(P) similar to those seen with one of 100 mg/kg/24 h. Changing the Na intake from 1,5 to 3 mEq/kg/24 h did not influence the C(P). There was no correlation between UP and UNa in any of the patient groups examined.