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Calcium - ionized



Ionized calcium is calcium that is freely flowing in your blood and not attached to proteins. It is also called free calcium.

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 used to measure the amount of ionized calcium in blood.

See also: Serum calcium

Alternative Names

Free calcium; Ionized calcium

How the test is performed

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.

How to prepare for the test

You should not eat or drink for at least 6 hours before the test. Your doctor may tell you to temporarily stop taking any drugs that can affect the test results. Calcium salts, hydralazine, lithium, thiazide diuretics, and thyroxine can increase your level of ionized calcium.

Never stop taking any medicine without first talking to your doctor.

How the test will feel

Why the test is performed

Your doctor may order this test if you have signs of kidney or parathyroid disease. The test may also be done to monitor persons who have already been diagnosed with such diseases.

Usually, blood tests measure your total calcium level, which looks at both ionized calcium and calcium attached to proteins. You may need to have a separate ionized calcium test if you have factors that increase or decrease total calcium levels, such as abnormal blood levels albumin or immunoglobulins.

Normal Values

Normal values may vary slightly from laboratory to laboratory.

  • Children: 4.4 - 6.0 milligrams per deciliter (mg/dL)
  • Adults: 4.4 - 5.3 mg/dL
What abnormal results mean

Greater-than-normal levels may be due to:

Lower-than-normal levels may be due to:

What the risks are


Fukagawa M, Kurokawa K, Papadakis MA. Fluid & electrolyte disorders. In: McPhee SJ, Papadakis MA, Tierney LM Jr. Current Medical Diagnosis and Treatment 2007. New York, NY: McGraw Hill; 2007.

Wysolmerski JJ, Insogna KL. The parathyroid glands, hypercalcemia, and hypocalcemia. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 266.

Review Date: 5/13/2009
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.
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