Iron tests are a group of blood tests that are done to evaluate the iron level in blood serum, the body's capacity to absorb iron, and the amount of iron actually stored in the body. Iron is an essential trace element; it is necessary for the formation of red blood cells and certain enzymes. At the other extreme, high levels of iron can be poisonous.
There are four different types of tests that measure the body's iron levels and storage. They are called iron level tests, total iron-binding capacity (TIBC) tests, ferritin tests, and transferrin tests. These tests are given for several reasons:
- to help in the differential diagnosis of different types of anemia
- to assess the severity of anemia and monitor the treatment of patients with chronic anemia
- to evaluate protein depletion and other forms of malnutrition
- to check for certain liver disorders
- to evaluate the possibility of chronic gastrointestinal bleeding (blood loss from the digestive tract is a common cause of iron deficiency anemia)
- to help diagnose certain unusual disorders, including iron poisoning, thalassemia, hemosiderosis, and hemochromatosis
A serum iron test can be used without the others to evaluate cases of iron poisoning.
Patients should not have their blood tested for iron within four days of a blood transfusion or tests and treatments that use radioactive materials. Recent high stress levels or sleep deprivation are additional reasons for postponing iron tests.
Blood samples for iron tests should be taken early in the morning because serum iron levels vary during the day. This precaution is especially important in evaluating the results of iron replacement therapy.
Iron tests are performed on samples of the patient's blood, withdrawn from a vein into a vacuum tube. The amount of blood taken is between 6 mL and 10 mL (1/3 of a fluid ounce). The procedure, which is called a venipuncture, takes about five minutes.
Iron level test
Serum iron level is increased in thalassemia, hemochromatosis, severe hepatitis, liver disease, lead poisoning, acute leukemia, and kidney disease. It is also increased by multiple blood transfusions and intramuscular iron injections.
Iron levels above 350–500 micrograms/dL are considered toxic; levels over 1000 micrograms/dL indicate severe iron poisoning.
Serum iron level is decreased in iron deficiency anemia, chronic blood loss, chronic diseases (lupus, rheumatoid arthritis), late pregnancy, chronically heavy menstrual periods, and thyroid deficiency.
Total iron-binding capacity (TIBC) test
The TIBC test measures the amount of iron that the blood would carry if the transferrin were fully saturated. Since transferrin is produced by the liver, the TIBC can be used to monitor liver function and nutrition.
Ferritin is increased in liver disease, iron overload from hemochromatosis, certain types of anemia, acute leukemia, Hodgkin's disease, breast cancer, thalassemia, infections, inflammatory diseases, and hemosiderosis. Ferritin levels may be normal or slightly above normal in patients with kidney disease.
Ferritin is decreased in chronic iron deficiency and severe protein depletion.
Before patients are tested for iron, they should be checked for any of the following factors:
- prescription medications that affect iron levels, absorption, or storage
- blood transfusion or radioactive medications within the last four days
- recent extreme stress or sleep deprivation
- recent eating habits; test results can be affected by eating large amounts of iron-rich foods shortly before the blood test
Patients scheduled for an iron level, TIBC, or transferrin test should fast for 12 hours before the blood is drawn. They are allowed to drink water. Patients scheduled for a ferritin test do not need to fast but they should not have any alcoholic beverages before the test.
Aftercare consists of routine care of the area around the venipuncture.
The primary risk is the possibility of a bruise or swelling in the area of the venipuncture. The patient can apply moist warm compresses if there is any discomfort.
The TIBC is decreased in malnutrition, severe burns, hemochromatosis, anemia caused by infections and chronic diseases, cirrhosis of the liver, and kidney disease.
A Manual of Laboratory and Diagnostic Tests. 5th ed. Ed. Francis Fishback. Philadelphia: Lippincott, 1996.
Pagana, Kathleen Deska. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis: Mosby, Inc., 1998.
Shaw, Michael, ed. Everything You Need to Know About Diseases. Springhouse, PA: Springhouse Corporation, 1996.
Rebecca J. Frey, PhD
Anemia—A disorder marked by low hemoglobin levels in red blood cells, which leads to a deficiency of oxygen in the blood.
Ferritin—A protein found in the liver, spleen, and bone marrow that stores iron.
Hemochromatosis—A disorder of iron absorption characterized by bronze-colored skin. It can cause painful joints, diabetes, and liver damage if the iron concentration is not lowered.
Iron poisoning—A potentially fatal condition caused by swallowing large amounts of iron dietary supplements. Most cases occur in children who have taken adult-strength iron formulas. The symptoms of iron poisoning include vomiting, bloody diarrhea, convulsions, low blood pressure, and turning blue.
Plasma—The liquid part of blood.
Siderophilin—Another name for transferrin.
Thalassemia—A hereditary form of anemia that occurs most frequently in people of Mediterranean origin.
Transferrin—A protein in blood plasma that carries iron derived from food intake to the liver, spleen, and bone marrow.