Hypertension Medicine And Elevated Serum Calcium

It is an unfortunate reality that medications prescribed by health care providers can have unwanted side effects. Such is the case with thiazide diuretics and the development of elevated serum calcium, also known as hypercalcemia. This is an important drug side effect, because thiazide diuretics are considered one of the first medications to use to treat high blood pressure, notes the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Commonly used thiazides include hydrochlorothiazide and chlorthalidone.

How Thiazides Work

Thiazides are a class of diuretics, or water pills, that act within the kidney. They block the action of a sodium-chloride channel. The end result is that sodium and chloride are not reabsorbed into the body and are eliminated in urine. Water is reabsorbed with sodium; therefore, with the loss of sodium reabsorption, the net effect is loss of water. The elevated serum calcium that results is not a direct effect of the thiazides.

How Thiazides Raise Calcium

While several mechanisms are proposed, the most commonly accepted relates to the activity of the sodium-calcium exchanger. The inside of the cells of the kidney become depleted in sodium due to the lack of reabsorption from the urine, therefore this sodium-calcium channel activity increases, exchanging sodium from the body for calcium that is present in the urine. The net result is increased sodium loss from the body and increased calcium reabsorption from the urine.

Epidemiology

Hypercalcemia does not occur in everyone who takes thiazide diuretics. In 2007 Robert A. Wermers, et al., reported that, in Olmsted County, Minnesota, the annual incidence of hypercalcemia induced by thiazides was 7.7 per 100,000. This occurred after a mean of six years from starting the medication. The average calcium level was 10.7 mg/dL, which is considered mild hypercalcemia and is typically asymptomatic. In addition, 64 percent of patients stopping thiazide did not normalize the serum calcium. The authors suggest that the development of hypercalcemia while taking a thiazide is related to underlying primary hyperparathyroidism. Primary hyperparathryoidism is a disorder of the parathyroid gland that results in high serum calcium levels.

Diagnosis and Management

Hypercalcemia is diagnosed with a blood test of the serum calcium level. Calcium is present in the blood bound to proteins, measured as a serum calcium, as well as in a free form, measured as ionized calcium. Typically, a serum and an ionized calcium are obtained to make the diagnosis of hypercalcemia. There are many causes of hypercalcemia. If an individual develops hypercalcemia while taking a thiazide, generally the practice is to stop the thiazide and continue to evaluate for other causes.