Hypercalcemia, a relatively common clinical problem, has become even more frequently recognized as autoanalyzer measurements of serum calcium have become routine on all serum samples drawn for electrolyte determinations. After the patient is recognized as having hypercalcemia, a number of diagnostic possibilities that might not have been considered previously are raised. Primary hyperparathyroidism is the most common cause in the ambulant population, and patients with this disorder are often asymptomatic. Current estimates are that primary hyperparathyroidism may have the astonishing annual incidence rate of 250 new patients per million population per year. In hospitalized patients, malignant disease is the commonest cause of hypercalcemia. In the following discussion the author reviews the multiple pathophysiologic mechanisms that have been linked with the presence of hypercalcemia in patients with malignant disease.
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