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

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 I 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.