Monomeric calcitonin secretion in infants with congenital hypothyroidism

We have determined CT levels in whole serum (iCT) and by an extraction method (exCT) in 25 infants affected by congenital hypothyroidism (CH)--11 athyreotic and 14 dysgenetic--at age 25 days, before the institution of therapy, and at age 2 years. In hypothyroid patients at age 25 days the iCT and exCT levels were similar to those found in controls of the same age. At age 2 years the iCT and exCT levels decreased in both groups of patients. However, whereas the levels of iCT in hypothyroids were similar to those found in controls of the same age, the levels of exCT were significantly lower in hypothyroids than in controls; moreover they were significantly lower in athyreotic than in dysgenetic patients. At this age, after calcium infusion, exCT levels significantly increased in dysgenetic but not in athyreotic patients. We hypothesize that CT deficiency in CH is due to increased degradation of human CT by the substitutive therapy, which, stimulating proteolytic enzymes, destroys the biologic activity of CT. An extraction procedure improves the sensitivity and specificity of the CT assay and it must be used when CT deficiency is suspected. In addition we suggest that the measurement of exCT levels after Ca infusion might be useful to distinguish dysgenetic from athyreotic patients.