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

Your health care provider will take blood sample from you. See: Venipuncture

A machine spins the blood to separate the cells from the liquid part of the blood (the serum). The amount of ionized calcium found in the serum is measured.

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.

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 calcium levels. For example, if you have abnormal amounts of albumin or immunoglobulins.

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

Greater-than-normal levels may be due to:

• Hyperparathyroidism
• Immobilization
• Metastatic bone tumor
• Milk-alkali syndrome
• Multiple myeloma
• Paget's disease
• Sarcoidosis
• Too muchvitamin D
• Certain types of tumors
• Use of thiazide diuretics

Lower-than-normal levels may be due to:

• Hypoparathyroidism
• Malabsorption
• Osteomalacia
• Pancreatitis
• Renal failure
• Rickets
• Vitamin D deficiency

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.