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Iron is an essential mineral the body needs to function properly. About 75% of the body's iron is a component of hemoglobin, the oxygen carrier in red blood cells. Not only is hemoglobin responsible for transporting oxygen from the lungs to all body cells, it gives red blood cells their characteristic color.
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Transferrin is a protein in the blood that transports iron from the intestines to cells in the body. The body makes this protein in relationship to the body's need for iron. When iron stores become low, transferrin levels will increase. When there is too much iron, transferrin levels are low. Normally, about 1/3 of the transferrin in the body is being used to transport iron.
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The remaining transferrin (not being used to transport iron) is the unsaturated iron binding capacity.
This is a blood test that measures the iron in the liquid part of the blood.
Serum iron plus UIBC equals TIBC (total iron binding capacity).
This blood test measures the amount of iron stored in the body (ferritin is the primary protein that stores iron).
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A high UIBC, TIBC, or transferrin normally indicates iron deficiency (pregnancy and oral contraceptives can also cause increased levels). A low UIBC, TIBC, or transferrin usually occurs in people with iron overload.
Transferrin saturation is low with iron deficiency and high when there is an excess amount of iron.
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The following are some disorders the above blood tests can diagnose:
Iron Deficiency Anemia
This is the most common type of anemia. It is caused by insufficient amounts of iron in the diet, the inability to absorb enough iron from the intestines, or blood loss. When iron levels are low, the cells operate with lowered energy. The primary symptom of iron deficiency is fatigue (tiredness). Pale skin, dizziness, cold hands or feet, headache, chest pain, and shortness of breath can also occur.
Iron is low, TIBC/transferrin is high, UIBC is high, transferrin saturation is low, and ferritin is low.
This type of anemia is caused by the destruction of red blood cells, either in the blood vessels or elsewhere in the body.
Iron is high, TIBC/transferrin is normal/low, UIBC is low/normal, transferrin saturation is high, and ferritin is high.
This anemia occurs when the body has iron but it is unable to incorporate it into hemoglobin.
Iron is normal/high, TIBC/transferrin is normal/low, UIBC is low/normal, transferrin saturation is high, and ferritin is high.
This disease is the most common type of iron overload that is either inherited or caused by a disorder like alcoholism. The body absorbs and stores too much iron. The extra iron builds up in the organs and causes damage. If untreated, this disease can cause serious problems like heart failure.
Iron is high, TIBC/transferrin is low, UIBC is low, transferrin saturation is high, and ferritin is high.
With iron poisoning, the unsaturated iron binding capacity is low, iron is high, TIBC/transferrin is normal, transferrin saturation is high, and ferritin is normal.
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Image courtesy of the National Institutes of Health.