Iron tests

Rebecca J. Frey

Definition

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.

Purpose

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.

Precautions

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.

Description

Iron tests are performed on samples of the patient's blood, withdrawn from a vein into a vacuum tube.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

The iron level test measures the amount of iron in the blood serum that is being carried by a protein (transferrin) in the blood plasma.

Medications and substances that can cause increased iron levels include chloramphenicol, estrogen preparations, dietary iron supplements, alcoholic beverages, methyldopa, and birth control pills.

Medications that can cause decreased iron levels include ACTH, colchicine, deferoxamine, methicillin, and testosterone.

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.

Medications that can cause increased TIBC levels include fluorides and birth control pills.

Medications that can cause decreased TIBC levels include chloramphenicol and ACTH.

Transferrin test

The transferrin test is a direct measurement of transferrin--which is also called siderophilin--levels in the blood. Some laboratories prefer this measurement to the TIBC. The saturation level of the transferrin can be calculated by dividing the serum iron level by the TIBC.

Ferritin test

The ferritin test measures the level of a protein in the blood that stores iron for later use by the body.

Medications that can cause increased ferritin levels include dietary iron supplements. In addition, some diseases that do not directly affect the body's iron storage can cause artificially high ferritin levels. These disorders include infections, late-stage cancers, lymphomas, and severe inflammations. Alcoholics often have high ferritin levels.

Preparation

Patient history

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.

Fasting

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

Aftercare consists of routine care of the area around the venipuncture.

Risks

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.

Normal results

Iron level test

Normal serum iron values are as follows:

• Adult males: 75-175 micrograms/dL
• Adult females: 65-165 micrograms/dL
• Children: 50-120 micrograms/dL
• Newborns: 100-250 micrograms/dL.

TIBC test

Normal TIBC values are as follows:

• Adult males: 300-400 micrograms/dL
• Adult females: 300-450 micrograms/dL.

Transferrin test

Normal transferrin values are as follows:

• Adult males: 200-400 mg/dL
• Adult females: 200-400 mg/dL
• Children: 203-360 mg/dL
• Newborns: 130-275 mg/dL.

Normal transferrin saturation values are between 30-40%.

Ferritin test

Normal ferritin values are as follows:

• Adult males: 20-300 ng/mL
• Adult females: 20-120 ng/mL
• Children (one month): 200-600 ng/mL
• Children (two to five months): 50-200 ng/mL
• Children (six months to 15 years): 7-140 ng/mL
• Newborns: 25-200 ng/mL.

Abnormal results

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.

TIBC test

The TIBC is increased in iron deficiency anemia, polycythemia vera, pregnancy, blood loss, severe hepatitis, and the use of birth control pills.

The TIBC is decreased in malnutrition, severe burns, hemochromatosis, anemia caused by infections and chronic diseases, cirrhosis of the liver, and kidney disease.

Transferrin test

Transferrin is increased in iron deficiency anemia, pregnancy, hormone replacement therapy (HRT), and the use of birth control pills.

Transferrin is decreased in protein deficiency, liver damage, malnutrition, severe burns, kidney disease, chronic infections, and certain genetic disorders.

Ferritin test

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.

Key Terms

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.

Hemosiderosis

An overload of iron in the body resulting from repeated blood transfusions. Hemosiderosis occurs most often in patients with thalassemia.

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.

Further Reading

For Your Information

Books

• Fischbach, Frances Talaska. A Manual of Laboratory and Diagnostic Tests. Philadelphia and New York: Lippincott, 1996.
• Mosby's Diagnostic and Laboratory Test Reference, edited by Kathleen Deska Pagana, and Timothy James Pagana. St. Louis: Mosby-Year Book, Inc., 1997.
• Springhouse Corporation. Everything You Need to Know About Medical Tests, edited by Michael Shaw et al. Springhouse, PA: Springhouse Corporation, 1996.

Gale Encyclopedia of Medicine. Gale Research, 1999.