Serum calcium is a laboratory test to measure the amount of calcium in your blood.

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.

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

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

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 or taking too much vitamin D as a dietary supplement can also increase 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.

This test is usually done to screen for bone diseases or diseases of the parathyroid gland or kidneys. It can also be done to monitor patients with such conditions.

A separate test measures calcium that is freely flowing in your blood and not attached to proteins. 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.

Higher-than-normal levels may be due to:

• Addison's disease
• Excessive vitamin D level
• Excessive calcium intake
• HIV/AIDS
• Hyperparathyroidism
• Metastatic bone tumor
• Milk-alkali syndrome
• Multiple myeloma
• Overactive thyroid gland (hyperthyroidism)
• Paget's disease
• Prolonged immobilization
• Sarcoidosis
• Tumors producing a parathyroid hormone-like substance
• Use of certain medications

Lower-than-normal levels may be due to:

• Hypoparathyroidism
• Kidney failure
• Liver disease (decreased albumin production)
• Low serum magnesium
• Malabsorption (inadequate absorption of nutrients from the intestinal tract)
• Osteomalacia
• Pancreatitis
• Rickets and vitamin D deficiency

Additional conditions under which the test may be performed:

• Delirium
• Dementia
• Multiple endocrine neoplasia (MEN) II
• Multiple endocrine neoplasia (MEN) I
• Renal cell carcinoma
• Secondary hyperparathyroidism

• 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

Goldman L, Ausiello D. Cecil Textbook of Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007.