Calcium blood test
The calcium blood test measures the level of calcium in the blood.
This article discusses the test to measure the total amount of calcium in your blood. About half of the calcium in the blood is attached to proteins, mainly albumin. For this reason, the calcium blood test can be misleading, and sometimes needs tests to confirm the result.
A separate test measures calcium that is not attached to proteins in your blood. Such calcium is called free or ionized calcium.
Calcium can also be measured in the urine.
Ca+2; Serum calcium; Ca++
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
The health care provider may tell you to temporarily stop taking certain medicines that can affect the test. Medicines 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 having an equivalent amount of other dairy products ) 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. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing or slight bruising. These soon go away.
Why the Test is Performed
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.
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
- Chronic kidney disease
- Chronic liver disease
- Disorders of the parathyroid gland
- 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.
Normal values range from 8.5 to 10.2 mg/dL.
Normal value ranges may vary slightly among different laboratories. Some laboratories use different measurements or may test different specimens. Talk to your doctor about the meaning of your specific test results.
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
- Consuming 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:
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- 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
Pincus MR, Abraham NZ Jr. Interpreting laboratory results. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 8.
Wysolmerski JJ, Insogna KL. The parathyroid glands, hypercalcemia, and hypocalcemia. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, Pa: Elsevier Saunders; 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, Bethanne Black, and the A.D.A.M. Editorial team.