Iron Tests

Iron status may be evaluated by ordering one or more tests to determine the amount of circulating iron in the blood, the capacity of the blood to transport iron, and the amount of stored iron in tissues.Testing may also help differentiate various causes of anemia and may include:

• Serum iron measures the level of iron in the blood.
• TIBC (total iron-binding capacity) measures all of the proteins in the blood that are available to bind with iron, including transferrin.Since transferrin is the primary iron-binding protein, the TIBC test is a good indirect measurement of transferrin.The body produces transferrin in relationship to the need for iron.When iron stores are low, transferrin levels increase and vice versa. In healthy people, about one-third of the binding sites on transferrin are used to transport iron.
• UIBC (unsaturated iron-binding capacity) measures the reserve capacity of transferrin, the portion of transferrin that has not yet been saturated.UIBC also reflects transferrin levels.
• Transferrin saturation is a calculation that is done with the iron test result and TIBC or UIBC.It represents the percentage of the transferrin that is saturated with iron.
• Serum ferritin reflects the amount of stored iron in the body; ferritin is the main storage protein for iron inside of cells.

These tests are often ordered together, and the results of each can help the doctor to determine the cause of iron deficiency or iron overload.

Several other tests can also be used to help recognize problems with iron status.

• Hemoglobin and Hematocrit are tests are performed as part of a complete blood count (CBC). A low value for either test indicates that a person has anemia. Iron deficiency is a very common cause of anemia. The average size of red cells (Mean Cell Volume or MCV) and the average amount of hemoglobin in red cells (Mean Cell Hemoglobin or MCH) are also measured in a CBC. In iron deficiency, insufficient hemoglobin is made, causing the red blood cells to be smaller and paler than normal. Both MCV and MCH are low.
• Reticulocyte count. The absolute number of reticulocytes (immature RBCs) is decreased in iron deficiency anemia but will increase to normal levels once iron therapy is received.
• Soluble transferrin receptor (sTfR). This test may be used to detect iron deficiency anemia and distinguish it from anemia caused by chronic illness or inflammation.
• Zinc Protoporphyrin (ZPP). Protoporphyrin is the precursor to the part of hemoglobin (heme) that contains iron. If there is not enough iron, another metal, such as zinc, will attach to the protoporphyrin instead. The amount of zinc protoporphyrin in red cells is increased in iron deficiency. ZPP is sometimes used as a screening test, especially in children. However, the test is not specific for iron deficiency, thus elevated values must be confirmed by other tests.
• HFE gene test. Hemochromatosis is a genetic disease, found primarily in Caucasians, that causes the body to absorb too much iron. It is usually due to an inherited abnormality in a specific gene, called the HFE gene, that affects the amount of iron absorbed from the gut. In people who have two copies of the abnormal gene, too much iron is absorbed and excess iron is deposited in many different organs, where it can cause damage and eventually organ failure. The HFE gene test determines whether a person has the mutations that cause the disease.The most common mutation is called C282Y.

One or more iron tests may be ordered when results from a routine CBC test are abnormal, such as a low hematocrit or hemoglobin, or when a doctor suspects that a person has iron deficiency due to the presence of signs and symptoms such as:

• Chronic fatigue/tiredness
• Dizziness
• Weakness
• Headaches
• Pale skin (pallor)

Ferritin, transferrin saturation, and a TIBC or UIBC may be ordered when a doctor suspects that a person may have a chronic iron overload (hemochromatosis).HFE genetic testing may be ordered to help confirm a diagnosis of hereditary hemochromatosis and sometimes when a person has a family history of hemochromatosis.

An iron test and sometimes TIBC and ferritin tests may be ordered when a person has symptoms that the doctor suspects are due to iron overload or poisoning.These may include:

• Joint pain
• Fatigue, weakness
• Lack of energy
• Abdominal pain
• Loss of sex drive
• Heart problems

When a child is suspected to have excessively ingested iron tablets, a serum iron test is ordered to detect and help assess the severity of the poisoning.

A summary of the changes in iron tests seen in various diseases of iron status is shown in the table below.

The mildest stage of iron deficiency is the slow depletion of iron stores. This means the amount of iron present is functioning properly but is being used up without adequate replacement. The serum iron level may be normal in this stage, but the ferritin level will be low. As iron deficiency continues, all of the stored iron is used and the body tries to compensate by producing more transferrin to increase iron transport. The serum iron level continues to decrease and transferrin and TIBC increase. As this stage progresses, fewer and smaller red blood cells are produced, eventually resulting in iron deficiency anemia.

When the iron level is high, the TIBC and ferritin are normal. If the person has a clinical history consistent with iron overdose, then it is likely that he has iron poisoning.Iron poisoning occurs when a large dose of iron is taken all at once or over a long period of time. While this is rare, it most commonly occurs in children who ingest their parents' iron supplements. In some cases, iron poisoning can be fatal.

A person who has two genetic mutations for HFE is diagnosed with hereditary hemochromatosis.However, many people who have hemochromatosis will have no symptoms for their entire life, while others will start to develop symptoms such as joint pain, abdominal pain, and weakness in their 30's or 40's.Iron overload may also occur in people who have hemosiderosis and in those who have multiple transfusions, such as may happen with sickle cell anemia, thalassemia, or other forms of anemia. The iron from each transfused unit of blood stays in the body, eventually causing a large buildup in the tissues. Some alcoholics with chronic liver disease also develop hemosiderosis.

Normal iron levels are maintained by a balance between the amount of iron taken into the body and the amount of iron lost. Normally, a small amount of iron is lost each day, so if too little iron is taken in, a deficiency will eventually develop. Unless a person has a poor diet, there is usually enough iron to prevent iron deficiency and/or iron deficiency anemia in healthy people. In certain situations, there is an increased need for iron. Persons with chronic bleeding from the gut (usually from ulcers or tumors) or women with heavy menstrual periods will lose more iron than normal and can develop iron deficiency. Women who are pregnant or breast feeding lose iron to their baby and can develop iron deficiency if not enough extra iron is taken in. Children, especially during times of rapid growth, may need extra iron and can develop iron deficiency.

Low serum iron can also occur in states where the body cannot use iron properly. In many chronic diseases, especially in cancers, autoimmune diseases, and with chronic infections (including AIDS), the body cannot properly use iron to make more red cells. As a result, production of transferrin decreases, and serum iron is low because little iron is being absorbed from the gut, and ferritin increases. Iron deficiency can also be seen in malabsorption diseases such as sprue syndrome (Celiac disease).