Normocalcemic hyperparathyroidism: Intervention to differentiate primary from secondary hyperparathyroidism

Normocalcemic hyperparathyroidism can occur, but surgery should not be considered until common etiologies for secondary hyperparathyroidism are comprehensively excluded. Calcium deficiency is an underrecognized cause of normocalcemic parathyroid hormone elevation, and we aim to determine if the implementation of a preoperative calcium challenge can be used to reduce unnecessary parathyroidectomy.

Consecutive patients referred for parathyroidectomy (1/21-6/22) with normocalcemia (serum calcium <10 mg/dL) and concurrently elevated parathyroid hormone levels were routinely treated with supplemental calcium and vitamin D3, and follow-up laboratory studies were assessed.

A total of 29/314 (9%) patients had normocalcemic parathyroid hormone elevation with mean calcium, parathyroid hormone, and vitamin D 25OH levels of 9.5 ± 0.3 mg/dL, 109.9 ± 34.9 pg/mL, and 42.7 ± 23.8 ng/mL respectively. Confounding factors included estimated glomerular filtration rate <60 in 2, loop diuretic use in 4, and prior gastric bypass or gastric sleeve surgery in 4. Follow-up biochemical evaluation was available in 27 (92%); results were unchanged in 7 patients (26%); normalization of parathyroid hormone levels with persistently normal calcium levels occurred in 15 (55%), thus confirming secondary hyperparathyroidism and hypercalcemia with elevated parathyroid hormone levels (classic primary hyperparathyroidism) was diagnosed in 5 (19%). Parathyroid exploration has been completed for 3 of 5 patients with classic primary hyperparathyroidism to date.

A preoperative calcium challenge was prospectively initiated in normocalcemic patients with parathyroid hormone elevation, and there was high compliance (92%). Short-interval calcium supplementation revealed ∼50% to have resolved secondary hyperparathyroidism due to insufficient calcium intake, which avoided unnecessary surgery. In contrast, classic patients were unveiled in 20%, allowing for prompt and correct surgical intervention.