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Calcium - blood test
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++
How the Test is Performed
A blood sample is needed. For information on how this is done, see: Venipuncture
How to Prepare for the Test
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)
- Thiazide diuretics
- 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.
How the Test Will Feel
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.
Why the Test is Performed
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.
What Abnormal Results Mean
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
- 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
- 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:
- 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.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.