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Patients experiencing symptoms of low iron levels, such as chronic fatigue, dizziness, weakness and headaches, should take a test to determine the iron saturation level. Similarly, patients experiencing symptoms associated with high iron levels, such as joint pain, abdominal pain, loss of sex drive and heart problems, should also take an iron saturation test.
Iron saturation tests are also given to patients that may have iron poisoning. This is commonly seen in children that have accidentally overdosed on vitamins or iron supplements.
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What Does the Test Measure?
The iron saturation level measures how well the body binds and transports iron. Specifically, it measures the transferrin-iron saturation percentage (TS%), which is calculated by dividing the serum iron level (SI) by the total iron binding capacity (TIBC) and multiplying by 100. The SI is the total amount of iron in the blood, and the TIBC is the total amount of iron that can be bound and transported by transferrin. Nearly all of the iron in the SI is bound to transferrin.
Transferrin is the protein which binds iron and transports it. When iron levels are low, more transferrin is available in the blood. When iron levels are high, fewer transferrin molecules are available. The amount of transferrin that isn't bound to iron is called the unsaturated iron binding capacity (UIBC). The TIBC equals the UIBC, plus the SI. Normally, about 1/3 of the transferrin available is bound to iron, while the remaining 2/3 of transferrin are available in reserve.
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How is the Test Performed?
To determine the iron saturation level, the serum iron level is measured from a sample of blood that is drawn from a vein. This is a blood test which is taken after a period of fasting. Certain foods and drinks must be avoided prior to taking the test including red meat, alcohol and vitamin c-rich fruit juices. Consuming these items will increase iron absorption and affect the level of iron in the blood.
A second blood sample is drawn to test for the TIBC. In this test, the maximum amount of iron that transferrin can bind is determined. This indirectly measures the availability of transferrin in the blood.
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Using the SI and the TIBC, the TS% is calculated. Normally, the TS% is between 20% and 40%. A TS% greater than 45% indicates iron loading, which is a build up of iron in the blood. This can lead to serious problems including arthritis, diabetes and liver cirrhosis. A TS% less than 20% indicates iron deficiency, which can lead to chronic illnesses.