A 52-year-old woman with asymptomatic primary hyperparathyroidism is being assessed for parathyroidectomy. Serum calcium is 10.6 mg/dL (laboratory upper limit 10.2), creatinine clearance is 78 mL/min, distal forearm T-score is minus 1.2, and she has never had renal stones. Which additional finding is by itself an accepted guideline indication for surgery?

• A 24-hour urinary calcium excretion of 430 mg/day ✓
• B Serum intact PTH twice the upper limit of normal
• C Serum magnesium at the lower limit of normal
• D Family history of thyroid nodules

Explanation

Guidelines for asymptomatic primary hyperparathyroidism recommend surgery when marked hypercalciuria (urinary calcium above 400 mg/day) coexists with increased stone risk, in addition to the classic markers: calcium more than 1 mg/dL above the upper limit, creatinine clearance below 60 mL/min, T-score of minus 2.5 or less, vertebral fracture, nephrocalcinosis or nephrolithiasis, and age below 50 years. An elevated PTH level defines the disease but is not itself an independent surgical indication, which removes option B.

Reference: Williams Textbook of Endocrinology, 14th ed.

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