Calcium metabolism after hemithyroidectomy

It is not known whether thyroid surgery evokes changes in calcium metabolism. We therefore studied 6 patients operated upon with hemithyroidectomy for benign thyroid diseases, preoperatively and at 3 months and 1 year postoperatively. We measured changes in serum levels of intact parathyroid hormone (PTH), vitamin D metabolites, ionized calcium, phosphate, osteocalcin, thyroid hormones and bone density. Further, the dynamic function of the parathyroid glands was investigated by an oral calcium load test pre- and at 3 months postoperatively. At follow-up, all patients were euthyroid. During the oral calcium load, serum levels of intact PTH were reduced by the same degree before and after hemithyroidectomy, showing normal parathyroid function. Serum levels of 1,25-dihydroxyvitamin D declined from 86 +/- 16 to 57 +/- 4 pmol/l (p < 0.01) at 1 year after hemithyroidectomy, and serum levels of phosphate increased slightly from 0.96 +/- 0.08 to 1.06 +/- 0.08 mmol/l (p < 0.05), whereas serum levels of ionized calcium, intact PTH, osteocalcin and bone density did not change. Our results demonstrate that thyroid operation evokes changes in vitamin D metabolism in spite of normal parathyroid function.