Primary hyperparathyroidism is the most common cause of high blood calcium levels, while cancer is the second most common cause, states the UCLA Health System. Other possible causes include use of thiazide diuretics and kidney disease. In rare cases, too much vitamin D, milk-alkali syndrome, thyroid disease or familial hypocalciuric hypercalcemia cause high blood calcium.
Doctors confirm a classic primary hyperparathyroidism diagnosis by testing for elevated parathyroid hormone levels, according to the UCLA Health System. Even if parathyroid levels are within normal ranges, a doctor may diagnose hyperparathyroidism if the parathyroid hormone levels are unusually high when compared to the calcium level.
Some cancers cause high blood calcium levels when the disease directly affects or spreads to the bones, explains Cancer.Net. Other cancers produce a protein that causes the body to release excessive amounts of calcium from the bones. Cancers that affect the kidneys also can prevent the kidneys from removing excess calcium from the body. Finally, immobility and dehydration, which are two symptoms common to many cancer patients, can cause hypercalcemia.
People with slightly elevated blood calcium levels may experience no symptoms of hypercalcemia, explains Mayo Clinic. Higher levels of calcium in the blood can trigger bone pain, muscle weakness, thirst and excessive urination. High calcium levels affect the brain, so people with hypercalcemia may experience fatigue, confusion and lethargy. Hypercalcemia can also trigger digestive problems, such as constipation, nausea, vomiting and abdominal pain.