Calcitonin Deficiency in Primary Hypothyroidism

The relative lack of sensitivity and specificity of current assays for plasma calcitonin (CT) have made it difficult to study possible CT deficiency conditions. Using a new extraction method that considerably improves the sensitivity of the assay for CT monomer, CT levels were measured before and after a short calcium (Ca) stimulation test (2 mg Ca/kg over 5 min) to determine C-cell secretory reserve in women with autoimmune primary hypothyroidism and normal women. Mean basal plasma CT concentrations were lower in the hypothyroid women [0.9 ±0.1 (±SEM) pg/ml] than in the normal women (1.5 ±0.2 pg/ml; P < 0.01). Serum Ca increased similarly in both groups, but postinfusion CT levels were lower in the women with primary hypothyroidism (3.8 ±1.3 pg/ml) than in normal women (15.9 ±3.0 pg/ml; P < 0.001). The functional thyroid status at the time of the study did not influence CT levels; both hypothyroid patients (n = 10) and patients who were euthyroid during T4 treatment (n = 11) were CT deficient to the same...