A 45-year-old man with mild hypercalcaemia (10.9 mg/dL) found on routine testing has a normal PTH of 60 pg/mL, normal renal function, and no symptoms. His brother has similar biochemistry. Twenty-four hour urinary calcium is 65 mg. What is the most appropriate next step?
- A Calculate the fractional excretion of calcium; a ratio below 0.01 supports familial hypocalciuric hypercalcaemia and no surgery ✓
- B Sestamibi scan followed by focused parathyroidectomy
- C Start cinacalcet and reassess in six months
- D Perform four-gland exploration with subtotal parathyroidectomy
Correct answer: A. Calculate the fractional excretion of calcium; a ratio below 0.01 supports familial hypocalciuric hypercalcaemia and no surgery
Explanation
Marked hypocalciuria with inappropriately normal PTH and a family history of similar biochemistry points to familial hypocalciuric hypercalcaemia, an autosomal dominant inactivating CASR mutation. The calcium to creatinine clearance ratio below 0.01 confirms it. It is benign, needs no treatment and no surgery, and parathyroidectomy fails to cure it because the defect is renal, not glandular. Operating on this patient is the classic exam trap.
Reference: Williams Textbook of Endocrinology, 13th ed.
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Written and medically reviewed by the StethoPrep medical team.