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Serum Iron 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:
Fast for 8 hours and ask your health care provider about avoiding food with high iron content before the test.
The health care provider may instruct you to discontinue drugs that can affect the test, including iron supplements (see special considerations).
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 experience, 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:
How it Feels:
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 .
Risks:
- excessive bleeding
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
Why this Test is Performed:
This test is performed when iron deficiency is suspected.
About 65% of the iron in the body is found 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 present in body fluids.
The body efficiently conserves iron so that only about 1 mg (men and post-menopausal women) or 1.8 mg (premenopausal adult women) is lost per day in the urine or menstrual blood. Since only about 10 to 15% of dietary iron is absorbed, even under optimum circumstances, this means that the recommended daily allowance (RDA, a guideline set by the United States Food and Drug Administration) for iron is 10 mg (men and post-menopausal women) and 18 mg (premenopausal adult women). Pregnancy greatly increases the need for iron, and iron deficiency is most common in women of reproductive age.
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 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: 20-50%
Note: mcg/dl = micrograms per deciliter
Abnormal Results:
Greater-than-normal levels may indicate: Lower-than-normal levels may indicate: Additional conditions under which the test may be performed:
Cost:
The estimated cost is $16.
Special Considerations:
Nonpharmacological factors that can effect iron measurements include a recent blood transfusion, the ingestion of food with a high iron content prior to the test, and the ingestion of iron supplements.
Drugs that can increase iron measurements include chloramphenicol, estrogens, oral contraceptives, and methyldopa.
Drugs that can decrease iron measurements include cholestyramine, chloramphenicol, colchicine, deferoxamine, methicillin, allopurinol, and testosterone .
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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