Low Serum Reverse T3 Levels in Patients with Primary Hyperparathyroidism

Summary

Although patients with primary hyperparathyroidism (1° HPT) were euthyroid, we measured serum thyroid hormone levels in 16 patients with 1° HPT together with 17 patients with hypercalcemia due to malignant diseases (HCM). In patients with 1° HPT, serum levels of T3, T4 and T3U were within normal range, but serum rT3 (reverse T3) levels (205±37 pg/ml, mean±SD) were significantly decreased as compared with those in normal controls (276±44 pg/ml, P < 0.01). A significant inverse correlation was observed between the serum levels of rT3 and parathyroid hormone (PTH) (r=0.54, P < 0.05). After parathyroidectomy, serum rT3 levels were significantly elevated (240±56 pg/ml) compared to preoperative levels (P < 0.01). Low levels of serum rT3 seemed to be attributed to the high levels of serum PTH. On the other hand, serum levels of T3 and T4 were low and serum rT3 levels were high in patients with HCM. Low serum rT3 allows for the differentiation of patients with 1° HPT from those with HCM.

Key-Words

Primary Hyperparathyroidism - Hypercalcemia Due to Malignant Diseases - Parathyroid Hormone - Reverse T3