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All cells need calcium in order to work. Calcium helps build strong bones and teeth. It is important for heart function, and helps with muscle contraction, nerve signaling, and blood clotting.

This article discusses the test to measure the total amount of calcium in your blood.

Calcium can also be measured in the urine. See: Calcium - urine test

Ca+2; Serum calcium; Ca++

A blood sample is needed. For information on how this is done, see: Venipuncture

Your health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test.

Drugs that can increase calcium levels include:

• Calcium salts (may be found in nutritional supplements or antacids)
• Lithium
• Thiazide diuretics
• Thyroxine
• Vitamin D

Drinking too much milk (two or more quarts a day) or taking too much vitamin D as a dietary supplement can also increase blood calcium levels.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Your doctor may order this test if you have signs or symptoms of:

• Certain bone diseases
• Certain cancers, such as multiple myeloma, a cancer of the breast, lung, neck, and kidney, especially during cancer treatment
• Chronic kidney disease
• Disorders of the parathyroid gland
• Chronic liver disease
• Disorders that affect how your intestines absorb nutrients
• Overactive thyroid gland or taking too much thyroid hormone medication

Your doctor may also order this test if you have been on bed rest for a long time.

About half of the calcium in the blood is attached to proteins. A separate test measures calcium that is not attached to proteins in your blood. Such calcium is called free or ionized calcium. See: Calcium - ionized

Normal values range from 8.5 to 10.2 mg/dL.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

Higher than normal levels may be due to a number of health conditions. Common causes include:

• Being on bed rest for a long time
• Taking too much calcium or vitamin D
• HIV/AIDS
• Hyperparathyroidism
• Infections that cause granulomas such as tuberculosis and certain fungal and mycobacterial infections
• Metastatic bone tumor
• Multiple myeloma
• Overactive thyroid gland (hyperthyroidism) or too much thyroid hormone replacement medication
• Paget's disease
• Sarcoidosis
• Tumors producing a parathyroid hormone-like substance
• Use of certain medications such as lithium, tamoxifen, and thiazides

Lower than normal levels may be due to:

• Hypoparathyroidism
• Kidney failure
• Liver disease
• Magnesium deficiency
• Disorders that affect absorption of nutrients from your intestines
• Osteomalacia
• Pancreatitis
• Vitamin D deficiency

• Excessive bleeding
• Fainting or feeling lightheaded
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

Wysolmerski JJ, Insogna KL. The parathyroid glands, hypercalcemia, and hypocalcemia. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 253.