Differential Diagnosis

Primary hyperparathyroidism

  • Excess parathyroid hormone (PTH) secretion from a single parathyroid adenoma, hyperplasia of the parathyroids, parathyroid carcinoma

Malignant tumors

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  • Especially tumors of the breast, lung, and kidney in which hypercalcemia may occur from direct bony metastasis

  • Multiple myeloma that directly degrades bone

  • Other cancers that produce hypercalcemia by inducing PTH secretion

Excess vitamin D intake

  • Prolonged use of diuretics and thiazides known to produce hypercalcemia

Dangerous Situations

Severe hypercalcemia favors a diagnosis of cancer.

Commonly Encountered Situations

Hypercalcemia from malignancy is especially common.

Suggested Additional Lab Testing

In primary hyperparathyroidism, serum PTH is increased and serum phosphorus is decreased.

In hypercalcemia of malignancy, serum phosphorus is decreased in approximately 50% of patients, and there is a decrease in the serum PTH in these patients.

Serum protein electrophoresis is useful in the assessment for multiple myeloma. Serum 1,25-dihydroxy vitamin D is low in hypercalcemia of malignancy. It is often increased in primary hyperparathyroidism.