[The calcium tolerance test in thyrotoxicosis, Hashimoto's thyroiditis and after total thyroidectomy]

Basic indicators of calcium and bone metabolism and the calcium tolerance test were investigated in patients with untreated hyperthyroidism, Hashimoto's thyroiditis, after total thyroidectomy and in controls. In florid hyperthyroidism elevated values of indicators of bone new formation (osteocalcin and bone fraction of alkaline phosphatases) and of bone resorption (urinary pyridinoline and deoxypyridinoline) were found and a protracted return of the serum calcium level to baseline values (during the 120th minute after completed infusion containing calcium). The calcitonin serum levels were significantly reduced after completion of the infusion up to the 120th minute. These results suggest a reduced calcitonin activity in hyperthyroidism, caused probably by exhaustion of C cells during the prolonged tendency of hypercalcaemia associated with untreated hyperthyroidism. In patients with autoimmune Hashimoto's thyroiditis no significant deviations in basal indicators of the calcium and bone metabolism were found nor deviations of the serum calcium and calcitonin levels during the calcium tolerance test. After total thyroidectomy the basal values of calcitoninaemia are significantly reduced and during the calcium tolerance test the elevated serum calcium level persists from the end of the calcium containing infusion up to the 120th minute. The calcitonin values are at all time intervals significantly low or cannot be detected (during the 120th and 240th minute). Changes of the serum calcium and calcitonin level are due to the surgical removal of the calcitonin source, thyroid C cells. The investigation confirmed the impaired calcium and bone metabolism and impaired calcium tolerance test in hyperthyroidism and in particular after total thyroidectomy. Reduced calcitonin values in these patients can act as a factor promoting the development of osteoporosis.