A blood test that measures the total iron binding capacity (TIBC) as an indirect measure of transferrin.
How the test is performed
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, and an elastic band is placed around the upper arm to apply pressure and 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 a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and 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 lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test
Fast for 8 hours before the test.
For infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- School age test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test is usually performed when iron deficiency is suspected as a cause of anemia.
About 65% of the iron in the body is carried in hemoglobin (in the red blood cells) and about 4% in myoglobin (in skeletal muscle). About 30% of the iron in the body is stored as a substance called ferritin in the liver, bone marrow, and spleen. A small percentage of the body’s iron is in transport, as part of a molecule called transferrin, traveling between various parts of the body via the blood stream.
A serum iron test actually measures the amount of iron in transferrin. Each transferrin molecule can carry 2 iron atoms, and normally, about 30% of the available “spaces” for iron are filled. By artificially 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
What abnormal results mean
Higher-than-normal TIBC may indicate:
- iron deficiency anemia
- pregnancy (late)
Lower-than-normal TIBC may indicate:
- hemolytic anemia
- pernicious anemia
- sickle cell anemia
- liver disease
Additional conditions under which the test may be performed:
- anemia of chronic disease
What the risks are
Risks associated with having blood drawn are slight:
- excessive bleeding
- fainting or feeling light-headed
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
Drugs that can increase TIBC measurements include fluorides and oral contraceptives.
Drugs that can decrease TIBC measurements 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. Obtaining a blood sample from some people may be more difficult than from others.
by Arthur A. Poghosian, M.D.