The finding of hypercalcemia on routine biochemical testing or in the evaluation of postmenopausal women with osteoporosis is typically the initial clue to the diagnosis of primary hyperparathyroidism. The total serum calcium level, which combines both the free and albumin-bound components of circulating calcium, should be adjusted for the level of albumin. Measurement of ionized calcium may be useful in selected cases, such as in patients with hyperalbuminemia, thrombocytosis, Waldenström's macroglobulinemia, and myeloma; these patients may have elevated levels of total serum calcium, but normal levels of ionized serum calcium (artifactual hypercalcemia).

Clinical hyperthyroidism, also called thyrotoxicosis, is caused by the effects of excess thyroid hormone and can be triggered by different disorders. Etiologic diagnosis influences prognosis and therapy.

Chagas' disease is caused by a protozoan parasite, Trypanosoma cruzi, that is transmitted to humans through the feces of infected bloodsucking insects in endemic areas of Latin America, or occasionally by nonvectorial mechanisms, such as blood transfusion. Cardiac involvement, which typically appears decades after the initial infection, may result in cardiac arrhythmias, ventricular aneurysm, congestive heart failure, thromboembolism, and sudden cardiac death.