Calcium and its regulating hormones in patients with graves disease: Sex differences and relation to postoperative tetany

Abstract

Objective: To find out why female sex is the most important risk factor for tetany, as calcium and bone metabolism may differ between the sexes. Design: Prospective study. Setting: Thyroid centre, Japan. Patients and Methods: 45 men (mean age 35 years, SD 13) and 178 women (mean age 33 years, SD 12) with Graves disease treated by subtotal thyroidectomy. Interventions: Measurement of serum concentrations of intact parathyroid hormone (iPTH), calcium, electrolytes, 25-hydroxyvitamin D (25 (OH) D), and 1,25-dihydroxyvitamin D (1,25 (OH) 2D). Main outcome measures: Mean values of these substances, together with reductions in serum calcium concentration, relative youth, increased alkaline phosphatase activity, large goitre, and increased serum TSH binding inhibitory globulin concentration. Results: Women had significantly lower calcium concentrations than men (mean (SD) 2.37 (0.13) compared with 2.43 (0.07), p = 0.003). Serum calcium concentrations correlated significantly with concentrations of 25 (OH) D (p < 0.001). 121 of the women (68%) compared with 13 (29%) of men had vitamin D deficiency as defined as 25 (OH) D < 25 nmol/l (p < 0.05). 15 patients (8%) developed tetany postoperatively compared with 1 man (2%, p = 0.2). Conclusion: Women with Graves disease are more susceptible to calcium and vitamin D deficiency than men, which may account for the higher incidence of postoperative tetany among women with the disease.