A 30-year-old woman is found to have a serum calcium of 2.95 mmol/L, PTH of 120 pg/mL (normal 10-65), and 24-hour urine calcium of 60 mg/day. She is asymptomatic and her DEXA scan is normal. The most likely diagnosis is:

• A Familial hypocalciuric hypercalcaemia (FHH) ✓
• B Primary hyperparathyroidism — adenoma
• C Tertiary hyperparathyroidism
• D Vitamin D deficiency with compensatory secondary hyperparathyroidism

Explanation

Familial hypocalciuric hypercalcaemia is characterised by hypercalcaemia, elevated PTH, and critically low urinary calcium excretion (calcium-to-creatinine clearance ratio <0.01). The 24-hour urine calcium of 60 mg/day is markedly low, differentiating FHH from primary hyperparathyroidism where urine calcium is typically elevated. FHH is caused by a loss-of-function mutation in the calcium-sensing receptor and parathyroidectomy is not curative and not indicated. Vitamin D deficiency causes hypocalcaemia, not hypercalcaemia.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.