Ionized Calcium Test

Written by Christine Case-Lo | Published on June 8, 2012
Medically Reviewed by Brenda B. Spriggs, MD, MPH, FACP

What Is an Ionized Calcium Test?

Calcium is an important mineral that is used in many ways in your body. It increases the strength of your bones and teeth and helps your muscles and nerves function. Total calcium in your blood is measured with a serum calcium blood test, but calcium is actually found in several different forms in your blood; these include free ionized calcium, calcium that is bound to other minerals (anions), and calcium that is bound to proteins like albumin. Ionized calcium is the most active form and is also called free calcium.

Why Is the Ionized Calcium Test Performed?

Typically, a serum calcium test is performed to check the total amount of calcium in your blood. This includes ionized calcium as well as all the calcium bound to proteins. If you have signs of kidney disease, certain kinds of cancers, or problems with your parathyroid gland, your doctor may want to check your blood calcium levels.

Ionized calcium levels give more information about active, ionized calcium. If you have abnormal levels of proteins, such as albumin, or immunoglobins in your blood, it may be important to know your ionized calcium levels. If the balance between bound calcium and free calcium is not normal, it’s important to determine why. Free and bound calcium each typically make up half of the body’s total calcium, and an imbalance can be a sign of a major health issue.

Patients receiving blood transfusions, critically ill patients on intravenous fluids, patients undergoing major surgery, and patients with abnormal levels of blood proteins may have their ionized calcium levels checked. In these patients, it is important to understand exactly how much free calcium is available.

Low levels of free ionized calcium can cause the heart to slow down or speed up, can cause muscle spasms, and can even result in coma. If you have any signs of numbness around your mouth or in your hands and feet, or experience muscle spasms in the same areas, an ionized calcium test may be ordered. These are symptoms of low free calcium levels.

This test is more difficult to perform than a serum calcium test due to the special handling required for the blood sample, so it is only done in certain circumstances.

How Is an Ionized Calcium Test Performed?

A small amount of your blood is needed to perform this test. The blood sample is obtained through “venipuncture,” in which a needle is inserted into a vein through the skin in your arm or hand, and a small amount of blood is drawn into a test tube.

How Do I Prepare for an Ionized Calcium Test?

For this test, you will need to fast (not eat or drink anything other than water) for six hours before you have your blood drawn.

You may have to stop taking certain medications before the test, but only if your doctor tells you to do so. Examples of drugs that can affect ionized calcium levels include calcium salts, hydralazine, lithium, thyroxine, and thiazide diuretics. Do not stop taking a medication unless your doctor tells you to.

What Are the Risks of an Ionized Calcium Test?

When the blood is collected, you may feel some moderate pain or a mild pinching sensation. After the needle is taken out, you may feel a throbbing sensation, and you will be instructed to apply pressure to the site where the needle entered your skin. A bandage will be applied that needs to remain in place for 10 to 20 minutes, and you should avoid using that arm for heavy lifting for the rest of the day.

There are some very rare risks involved in taking a blood sample, including:

  • lightheadedness or fainting
  • hematoma (blood accumulates under the skin)
  • infection (usually prevented by cleaning the skin before the needle is inserted)
  • excessive bleeding (bleeding for a long period afterwards may indicate a more serious bleeding condition and should be reported to your doctor)

What Is a Normal Result for an Ionized Calcium Test?

Normal levels of free ionized calcium are different in adults and children. In adults, a level of 4.64 to 5.28 mg/dL (milligrams per deciliter) is normal. In children, a normal ionized calcium level is 4.8 to 5.52 mg/dL.

What Does an Abnormal Ionized Calcium Test Result Mean?

Abnormal results can indicate kidney disease, problems with your parathyroid gland, vitamin and mineral deficiencies, certain kinds of cancer, and the effects of certain medications.

Low levels of ionized calcium in the blood can indicate:

  • hypoparathyroidism (underactive parathyroid gland)
  • inherited resistance to parathyroid hormone
  • malabsorption of calcium
  • vitamin D deficiency
  • osteomalacia/rickets (softening of the bones, in many cases due to a vitamin D deficiency)
  • magnesium deficiency
  • high phosphorus levels
  • acute pancreatitis (inflammation of the pancreas)
  • kidney failure
  • malnutrition
  • alcoholism

High level of ionized calcium in the blood can indicate:

  • hyperparathyroidism (overactive parathyroid gland)
  • sedentary lifestyle (lack of mobility)
  • milk-alkali syndrome (high levels of calcium and alkaline in the body due to excessive milk and antacid consumption over time)
  • multiple myeloma (cancer of the plasma cells, a type of white blood cell that produces infection-fighting antibodies)
  • Paget’s disease (disorder that results in deformity due to abnormal bone destruction and growth)
  • sarcoidosis (inflammatory disease of unknown origin affecting the eyes, skin and other organs)
  • tuberculosis (potentially fatal disease caused by the bacterium Mycobacterium tuberculosis which normally attacks the lungs)
  • kidney transplant
  • taking thiazide diuretics
  • certain kinds of tumors
  • overdose of vitamin D
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