A 28-year-old asymptomatic man is found on routine testing to have calcium of 10.9 mg/dL with PTH of 70 pg/mL (normal 15 to 65). His father had similar biochemistry and never needed surgery. Renal function is normal and sestamibi scan is negative. Which single test best avoids unnecessary neck exploration?

• A Calcium to creatinine clearance ratio ✓
• B 24-hour urinary calcium excretion alone
• C Bone mineral density by DEXA
• D Vitamin D level

Explanation

Familial hypocalciuric hypercalcaemia mimics mild primary hyperparathyroidism but needs no operation. The discriminating test is the fractional calcium clearance ratio, calculated as (urine calcium x plasma creatinine) divided by (plasma calcium x urine creatinine); a value below 0.01 supports FHH, while values above 0.02 favour primary hyperparathyroidism. In FHH the kidney conserves calcium, so urinary calcium is disproportionately low relative to filtered load. Surgery in FHH fails to cure and removes normal glands.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.