Calcitonin levels are similar in goitrous euthyroid patients with or without thyroid antibodies, as well as in hypothyroid patients

Objective: Some authors, after studying retrospectively immunostained sections of thyroid specimens, found C-cell hyperplasia (CCH) unrelated to medullary thyroid carcinoma to be frequent in thyroid glands affected by chronic lymphocytic thyroiditis (CLT); others failed to observe this association. The purpose of the present study was to further investigate prospectively the existence of the proposed relationship between CLT and CCH by measuring circulating calcitonin (CT) levels. Design: Basal serum CT was measured in 174 euthyroid goitrous women with negative thyroid autoantibodies (TA-Neg) and 124 age-matched goitrous euthyroid women with positive antibodies (TA-Pos). A calcium-infusion test was performed in 27 TA-Neg and 31 TA-Pos age-matched euthyroid goitrous women. Basal CT was also determined in 51 hypothyroid women and 40 control normal healthy women. Methods: Serum CT was measured using a specific and sensitive two-site immunoassay which detects mainly the CT-32 monomer, Thyroid autoantibodies (anti-thyroid peroxidase and anti-thyroglobulin) were measured in serum by quantitative RIAs. Results: Basal serum CT was found to be similar in TA-Neg and TA-Pos euthyroid as well as hypothyroid and normal control groups. A test of independence performed on the frequency distribution of the patients among sequential classes of serum CT showed that basal CT levels are independent of the presence of thyroid autoantibodies or hypothyroidism. Calcium-stimulated CT as well as the increase in CT were similar in TA-Neg and TA-Pos euthyroid goitrous women. There was no correlation between thyrotropin and CT in the hypothyroid group. Conclusion: Positive thyroid antibodies in goitrous patients do not predispose to hypercalcitoninemia. Elevated CT found in a patient with goitre and positive thyroid antibodies should not be ascribed to the underlying thyroiditis; this patient should be investigated for some other cause of the high CT.