ACP InternistMKSAP Quiz: Follow-up of Hypoparathyroidism

Diagnosing Hypoparathyroidism: Would You Measure 25-Hydroxyvitamin D, Ionized Calcium, Parathyroid Hormone, or Serum Phosphorus?

A 57-year-old man is being evaluated during routine follow-up of hypoparathyroidism. He underwent resection of locally advanced squamous cell carcinoma of the tongue base with laryngectomy, thyroidectomy, tracheostomy, and percutaneous gastrostomy tube placement 2 years ago. He also received adjuvant radiation therapy. Hypoparathyroidism developed after treatment. He has no evidence of cancer recurrence and has maintained a normal weight and hydration.

The patient is currently on levothyroxine, calcium citrate, calcitriol, hydrochlorothiazide, and potassium chloride. Serum calcium, magnesium, and urine calcium excretion were all measured.

Given the patient’s history and current condition, what additional measurements should be obtained for management of this patient’s hypoparathyroidism?

• 25-Hydroxyvitamin D. This reflects dietary and skin-derived vitamin D. However, activation of vitamin D to 1,25-dihydroxyvitamin D requires both PTH and sufficient kidney function.
• Ionized Calcium. Measured calcium levels depend on the amount bound to albumin, which can be affected by nutrition and acid-base status. Hypoalbuminemia of any cause will cause low total calcium levels.
• Parathyroid Hormone (PTH). During the assessment of new-onset hypocalcemia, measurement of PTH establishes the mechanism of disease and guides treatment.
• Serum Phosphorus. Loss of PTH-mediated renal excretion of phosphorus may result in hyperphosphatemia. In hypoparathyroidism management, serum phosphorus concentrations are ideally maintained in the normal range.

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