Serum calcitonin concentrations in premature infants during the first 12 weeks of life.

Twenty-eight premature infants of mean gestation 30.9 +/- 2.5 weeks and mean birth weight 1175 +/- 206 g had repeated serum calcitonin concentrations determined over the first 12 weeks of life. Serum calcitonin concentrations slowly fell but remained elevated even at 12 weeks of age [normal adult = 71 +/- 48, 1 week (N = 15) = 327 +/- 167, 3 week (N = 23) = 270 +/- 129, 6 week (N = 16) = 249 +/- 154, 9 week (N = 13) = 214 +/- 108, 12 week (N = 12) = 174 +/- 11]. Throughout this period, serum total calcium was normal or low (8.4 +/- .8-9.3 +/- 1.0). Serum phosphorus was normal or low (6.0 +/- 1.4-6.5 +/- 1.0), and serum magnesium was normal (1.7 +/- 0.24-1.8 +/- 0.34). The reason for the sustained elevation of serum calcitonin in these very small, sick, premature infants in unclear.