What Does It Mean If Blood Work Shows High Calcium Levels?

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.