Circulating calcitonin levels in healthy children and subjects with congenital hypothyroidism from birth to adolescence.

Using an extraction-concentration technique of circulating calcitonin (exCT) that permits a sensitive and specific assessment of circulating CT monomer levels, we measured exCT levels in 115 healthy children (59 girls and 56 boys), aged 0-16 yr, and 25 patients (15 girls and 10 boys), aged 2 months to 22 yr, with congenital hypothyroidism (CH), a condition characterized by a marked CT deficiency in adults. We found a significant negative correlation between CT levels and age in healthy children (girls, r = -0.83; boys, r = -0.63; P < 0.001). There was a 5-fold decrease in CT levels from the neonatal period to adolescence. The fall in CT levels was particularly marked in early infancy (e.g. for the age category 1 day to 1 yr, 19.0 +/- 1.9 vs. 7.3 +/- 1.2 ng/L for the group 1-5 yr, P < 0.01), but less pronounced thereafter (for the group 5-10 yr, 4.7 +/- 0.8 ng/L; P < 0.001 vs. the group 1 day to 1 yr). The well established sex difference in CT levels in adults was significant only for the age category above 10 yr (2.7 +/- 0.4 ng/L for girls vs. 4.5 +/- 0.7 ng/L for boys, P < 0.05). In patients with CH, the mean exCT level was 2.0 +/- 0.3 ng/L under 3 yr of age (n = 9), whereas all CT values were undetectable after the age of 3 yr, which could contribute to the lower bone mass of adult CH patients. CT values were normal in 3 children with metabolic goiter. In healthy children, our results demonstrate the existence of an age-related decrease in circulating CT levels, which was particularly marked in infancy. The sex difference in CT levels progressively appeared in childhood, but was significant only after 10 yr of age. Such changes in CT levels could be important for neonatal calcium metabolism and contribute to the lower bone mass in females.