Definition of 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

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:

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.

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 of albumin or immunoglobulins.