Studies on circulating immunoreactive calcitonin in low birth weight infants during the first 48 hours of life.

Serum immunoreactive calcitonin (iCT), serum immunoreactive parathyroid hormone (iPTH) and serum Ca, Mg, P and total protein levels were determined sequentially at 5 given periods of time from 1 to 48 h of age in 16 low birth weight infants. Mean +/- SD serum Ca levels decreased from 8.99 +/- 0.79 mg/100 ml at time 1--2 h to 7.00 +/- 0.51 mg/100 ml at time 12--14 h; there was a small further decrease at time 22--26 h: 6.79 +/- 1.07 mg/100 ml. There was no significant change in serum Mg, P or total protein during the same periods of time. Serum iPTH levels increased steadily from time 1--2 h to time 44--48 h reaching above normal range values. Serum iCT levels were non detectable (less than 150 pg/ml) in 11 among 15 infants at time 1--2 h. A marked increase in mean +/- SD serum iCT levels was observed at time 12--14 h (1850 +/- 872 pg/ml) and time 22--26 h (1462 +/- 806 pg/ml) followed by a decrease at time 44--48 h. A negative correlation was found between serum iCT levels and respectively gestational age (p less than 0.01) and serum Ca levels (p less than 0.01) at time 22--26 h while serum iCT levels correlated positively with serum iPTH levels (p less than 0.05). Evidence obtained from this study indicates that a secretion of calcitonin takes place during the early neonatal period in low birth weight infants and that this secretion is a contributing factor of the socalled "early-type" neonatal hypocalcemia.