Laboratory results presented are most compatible with which condition?

• A. Multiple myeloma
• B. Milk-alkali syndrome
• C. Sarcoidosis
• D. Primary hyperparathyroidism

Answer: (D)

High calcium with a non-suppressed (inappropriately normal or elevated) parathyroid hormone points to primary hyperparathyroidism. In this condition overactive parathyroid tissue raises serum calcium through three main actions: stimulating bone resorption, increasing renal calcium reabsorption, and enhancing gut calcium absorption via increased production of active vitamin D. At the same time, PTH causes phosphate excretion in the kidneys, so serum phosphate often falls. Alkaline phosphatase may be elevated due to increased bone turnover.

This pattern helps distinguish it from the other conditions. Milk-alkali syndrome would typically show metabolic alkalosis with hypercalcemia and often kidney impairment, and PTH would be suppressed. Sarcoidosis causes hypercalcemia mainly from extra-renal production of active vitamin D, with suppressed PTH. Multiple myeloma leads to hypercalcemia with accompanying features like anemia, renal issues, bone lesions, and a monoclonal protein, with PTH not driving the process.