Impaired parathyroid response to induced hypocalcemia in thalassemia major.

Ethylene diamine tetra-acetic acid-induced hypocalcemia was used as provocative test of parathyroid reserve in eight normocalcemic patients with thalassemia major (age 8 to 26 years) and five young adult control subjects (age 22 to 35). In response to an intravenous infusion of disodium EDTA (50 mg/kg), serum immunoreactive parathyroid hormone rose by 1.97 +/- 1.93 (SD) microliterEq/ml in the patients, controls showing a rise of 10.6 +/- 3.6 microliterEq/ml (t = 5.46, P less than 0.001). There was no relationship between parathyroid response and total iron burden as measured by serum ferritin- or desferrioxamine-induced urinary iron excretion. Impairment of parathyroid reserve is common in transfused patients with thalassemia major and may serve as a marker of significant iron overload.