Differential Diagnosis
Primary hyperparathyroidism
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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
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Multiple myeloma that directly degrades bone
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Other cancers that produce hypercalcemia by inducing PTH secretion
Excess vitamin D intake
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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.
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