Late evolution of serum immunoreactive parathyroid hormones, calcitonin and plasma 25-hydroxy cholecalciferol concentrations in very low birthweight infants.

The plasma concentrations of 25-hydroxycholecalciferol (25-OH-CC), immunoreactive parathyroid hormone (iPTH) and calcitonin (iCT) were measured at the age of 30 and 66 days in thirteen preterm neonates (birthweight: 970 to 1300 g). At the age of 30 days when all infants were fed only with breast milk (BM) serum iCT and iPTH levels were normal. During the second month 7 infants were fed with BM only (control group) and 6 infants were supplemented with formula (supplemented group). At the age of 66 days, mean +/- S.D. serum iPTH concentration was higher in the supplemented group than in the control group: 169 +/- 79 vs. 60 +/- 33 microliterEq/ml (p less than 0.01). Serum iCT levels remained undetectable (less than 150 pg/ml) in both groups. Plasma 25-OH-CC concentrations were normal and similar in both groups. Serum iPTH concentrations were positively correlated with phosphorus intake and negatively correlated with calcium intake from BM only. The results suggest that secondary hyperparathyroidism can be detected in very low birthweight infants supplemented with a formula, probably because of a phosphorus load or decreased intestinal absorption of calcium.