Endocrine Abstracts

Introduction: Primary hyperparathyroidism (PHPT) is disorder of one or more parathyroid glands, characterized by inadequately increased PTH secretion, almost always followed by hypercalcemia. Calcitonin, secreted by parafollicular C-cells in thyroid gland, is hypocalcemic hormone which partly acts as physiological antagonist of PTH.

Aim: To evaluate calcitonin response in calcium infusion test in patients with primary hyperparathyroidism.

Method: Study consisted of 15 patients with confirmed PHPT (57.20±11.38yrs) and 15 healthy subjects-HC (57.20±11.41yrs) matched for age and gender. In all subjects, basal levels of total serum calcium (Ca), ionized calcium (Ca²⁺), phosphate (P), PTH levels were measured. Calcium infusion test (CIT) was performed in all subjects when ionized calcium, calcitonin and PTH were measured in −30, 0, 1, 2, 3, 5, 8, 10 min after calcium infusion. Statistical analysis included Spearman correlation, Student T test.

Results: Basal levels of Ca, Ca²⁺, PTH were statistically significantly higher in PHPT group compared to HC (Ca:2.83±0.25 vs 2.41±0.06 mmol/l, Ca²⁺:1.44±0.14 vs 1.16±0.04 mmol/l, PTH (128.20±91.76 vs 41.77±12.83 ng/l). There was no statistical difference in calcitonin levels between groups (6.60±3.94 vs 6.76±2.97 ng/l). In CIT, maximum increase of Ca²⁺ was registered in 1.minute in both groups. After calcium infusion, average maximum calcitonin levels were 20.42±11.40 ng in PHPT group in the 1.minute with gradual decrease up to 10.81±7.80 ng/l in 10.minute. In HC group average maximal levels of calcitonin were 38.89±24.51 ng/l in 2.minute with gradual decrease up to 21.74±9.52 ng/l in 10.minute.

Conclusion: We showed decreased response of calcitonin in calcium infusion test in patients with PHPT compared to healthy subjects. This is in accordance with some earlier studies. In chronic hypercalcemia, responsiveness of C-cells is decreased on acute increase of serum calcium levels. In PHPT there is up regulation of calcitonin secretion set-point, depending on calcium levels.