Serum calcitonin in hyperthyroidism.

The mineral content of the radius was found to be lower in thyrotoxic than in euthyroid women, particularly in the case of elevated serum triiodothyronine levels. On examining the hormones influencing bone metabolism, the basal serum calcitonin level of thyrotoxic patients was identical with that of the controls. The Ca and calcitonin responses to i.v. Ca loading (3.64 mg CaCl2/kg/3 min) were identical in the euthyroid and hyperthyroid subjects. The results suggest that the calcitonin reserves in Graves' disease are normal and that the bone abnormalities typical of this disease are unrelated to any change in calcitonin secretion. The serum calcitonin levels of patients with subacute thyroiditis were identical with those of the controls. An acute fall in the serum calcitonin level occurred in hyperthyroidism, after radioiodine therapy a finding which might be connected with the high radiosensitivity of the parafollicular cells and with a consecutive impairment of calcitonin production.