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Calcium - ionized

Ionized calcium is calcium in your blood that is 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. It also helps with muscle contraction, nerve signaling, and blood clotting.

This article discusses the test used to measure the amount of ionized calcium in blood.

Alternative Names

Free calcium; Ionized calcium

How the test is performed

A blood sample is needed. Most of the time blood is drawn from a vein located on the inside of the elbow or the back of the hand.

How to prepare for the test

You should not eat or drink for at least 6 hours before the test.

Many medicines can interfere with blood test results.

  • Your health care provider will tell you if you need to stop taking any medicines before you have this test.
  • Do not stop or change your medications without talking to your doctor first.

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 progress and treatment of these diseases.

Most of the time, blood tests measure your total calcium level. This 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. These may include abnormal blood levels of albumin or immunoglobulins.

Normal Values

  • Children: 4.4 - 6.0 milligrams per deciliter (mg/dL)
  • Adults: 4.4 - 5.3 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 of ionized calcium may be due to:

Lower-than-normal levels may be due to:

References

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.

Updated: 5/5/2013

David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.


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