| Definition: |
A blood test that measures the total iron binding capacity (TIBC) as an indirect measure of transferrin.
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| Alternative Names: |
Total iron binding capacity
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| How the test is performed: |
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (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 tourniquet 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.
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.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| 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 in hemoglobin (in red blood cells) and about 4% in myoglobin (in skeletal muscle). About 30% of the iron in the body is stored (as ferritin or hemosiderin) in liver, bone marrow, and reticuloendothelial cells of the spleen. A small percentage of the body's iron is in transport between various compartments of the body (in association with transferrin) or is a component of enzymes in cells throughout the body. Free iron is very reactive (it stimulates free radical reactions) and is not normally in body fluids.
Serum iron, as measured in the clinical laboratory, is really transferrin-associated ferric iron. Each transferrin molecule can carry 2 iron atoms. Normally about 30% of the available sites are filled. This is called the percent transferrin saturation. By completely saturating all the available binding sites, it is possible to measure the total iron binding capacity (TIBC). This is really a measure of the transferrin level in the serum. TIBC is usually elevated when total body iron stores are low. TIBC and percent transferrin saturation are usually measured at the same time serum iron is measured. |
| Normal Values: |
- iron: 60 to 170 mcg/dl
- TIBC: 240 to 450 mcg/dl
- transferrin saturation: 20 to 50%
Note: mcg/dl = micrograms per deciliter |
| What abnormal results mean: |
| Greater-than-normal TIBC may indicate:Lower-than-normal TIBC may indicate:Additional conditions under which the test may be performed:
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| What the risks are: |
Risks associated with venipuncture 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
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| Special considerations: |
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. |
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