Total iron binding capacity (TIBC) is a blood test that shows if there is too much or too little iron in the blood. This test helps measure the ability of a protein called transferrin to carry iron in the blood.

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or an attached tube (syringe). The band is removed to restart blood flow. Once the blood has been collected, the needle is removed. The puncture site is covered to stop any bleeding.

For an infant or young child:

The area is cleansed with antiseptic and punctured with a sharp needle or a small pointed blade (lancet). The blood may be collected in a small glass tube (pipette), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be placed on the puncture site if bleeding continues.

You should not eat or drink for 8 hours before the test.

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

This test is usually done when the health care provider suspects low iron (deficiency) as a cause of anemia.

About 65% of the iron in the body is carried in a part of red blood cells called hemoglobin. About 4% of iron is carried in a part of muscle tissue called myoglobin. About 30% of the iron in the body is stored as a substance called ferritin in the liver, bone marrow, and spleen. A small amount of the body's iron moves through the body in the blood stream as part of a protein called transferrin.

A serum iron test measures the amount of iron in transferrin. Each transferrin molecule can carry 2 iron atoms. Normally, about 30% of the free "spaces" for iron in transferrin are filled. By filling up all the available spaces, doctors can measure the total iron binding capacity, or TIBC, of your blood. TIBC is usually higher-than-normal when the body's iron stores are low.

• Iron: 60-170 mcg/dl
• TIBC: 240-450 mcg/dl
• Transferrin saturation: 20-50%

Note: mcg/dl = micrograms per deciliter

Higher-than-normal TIBC may mean:

• Iron deficiency anemia
• Pregnancy (late)

Lower-than-normal TIBC may mean:

• Cirrhosis
• Hemolytic anemia
• Hypoproteinemia
• Pernicious anemia
• Sickle cell anemia
• Inflammation
• Malnutrition
• Liver disease

Other conditions under which the test may be done:

• Anemia of chronic disease

Risks from having blood drawn include:

• Excess bleeding
• Fainting or feeling light-headed
• Blood under the skin (hematoma)
• Infection
• Many needle pricks to find veins

Drugs that can raise TIBC include fluorides and oral birth control medications.

Drugs that can lower TIBC include ACTH and chloramphenicol.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Getting a blood sample from some people may be harder than from others.

McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders, 2006.

Rakel RE. Textbook of Family Practice. 6th ed. Philadelphia, Pa: Saunders, 2001.