Causes include the following: Increased parathyroid hormone levels, as in primary and secondary hyperparathyroidism Other hormonal disturbances, such as Cushing syndrome and hypothyroidism Vitamin Ddeficiency Electrolyte disorders, such as hypomagnesemia and hypokalemia Long-term diuretic use Theophylline intoxication Severe chronic hypophosphatemia usually results from a prolonged negative phosphate balance.