Also known as:Fe Tests; Iron Indices
Formal name:Iron Tests
Related tests:Serum Iron, Ferritin; TIBC, UIBC and Transferrin; Zinc Protoporphyrin; Complete Blood Count; Hemoglobin; Hematocrit; Reticulocyte Count; Soluble Transferrin Receptor
Why Get Tested?
To evaluate your body's current level of iron
When to Get Tested?
When your doctor suspects that you may have too little or too much iron in your system
A blood sample drawn from a vein in your arm
Test Preparation Needed?
Your doctor may request that you fast for 12 hours prior to some iron tests; in this case, only water is permitted.
How is it used?
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.
When is it ordered?
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
- 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.
What does the test result mean?
A summary of the changes in iron tests seen in various diseases of iron status is shown in the table below.
|Disease||Iron||TIBC/Transferrin||UIBC||% Transferrin Saturation||Ferritin|
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.
Is there anything else I should know?
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).
What is being tested?
Iron is an essential nutrient to maintain life. It is needed in small quantities to help form normal red blood cells (RBCs) and is a critical part of hemoglobin, the protein in RBCs that binds oxygen in the lungs and releases it as blood circulates to other parts of the body.
Iron tests are ordered to evaluate the amount of iron in the body by measuring several substances in the blood. These tests are often ordered at the same time, where together, the results are considered in establishing the diagnosis and/or monitoring iron deficiency or iron overload.
- Serum iron measures the level of iron in the liquid portion of the blood.
- TIBC (total iron-binding capacity) measures all of the proteins in the blood that are available to bind with iron, including transferrin.
- UIBC (unsaturated iron-binding capacity) measures the portion of transferrin that has not yet been saturated. UIBC also reflects transferrin levels.
- Transferrin saturation is a calculation that reflects the percentage of transferrin that is saturated with iron.
- Serum ferritin reflects the amount of stored iron in the body.
Low iron levels can lead to anemia, causing decreased production of RBCs that are microcytic and hypochromic. Conversely, large quantities of iron can be toxic to the body. This occurs when too much iron is absorbed over time, leading to the accumulation of iron compounds in tissues, particularly the liver, heart, and pancreas.
Iron is normally absorbed from food and transported throughout the body by binding to transferrin, a protein produced by the liver. About 70% of the iron transported is incorporated into the production of red blood cell hemoglobin. The remainder is stored in the tissues as ferritin or hemosiderin, with additional small amounts used to produce other proteins such as myoglobin and some enzymes.
Iron deficiency may be seen with insufficient intake, inadequate absorption, or increased nutrient requirements as seen during pregnancy or with acute or chronic blood loss. Acute iron overload may often occur with excess ingestion of iron tablets, especially in children. Chronic iron overload may be due to excessive iron intake, hereditary hemochromatosis, multiple blood transfusions, and a few other conditions.
How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Fasting for 12 hours before sample collection may be required. In this case, only water is permitted.
- Is iron deficiency the same thing as anemia? What are the symptoms?
Iron deficiency refers to a decrease in the amount of iron stored in the body, while iron deficiency anemia refers to a drop in the number of red blood cells (RBCs) and/or the amount of hemoglobin within the RBCs. It typically takes several weeks after iron stores are depleted for the level of hemoglobin and production of RBCs to be affected and for anemia to develop. There usually are few symptoms early in iron deficiency, but as the condition worsens and blood levels of hemoglobin and RBCs decrease, then ongoing weakness and fatigue can develop.
As your iron continues to be depleted, you may have shortness of breath and dizziness. If the anemia is severe, chest pain, headaches, and leg pains may occur. Children may develop learning (cognitive) disabilities. Besides the general symptoms of anemia, there are certain symptoms that are characteristic of iron deficiency. These include pica (cravings for specific substances, such as licorice, chalk, dirt, or clay), a burning sensation in the tongue or a smooth tongue, sores at the corners of the mouth, and spoon-shaped finger- and toe-nails.
- What are some causes of anemia besides iron-deficiency?
There are many different conditions that can cause anemia other than iron deficiency. Some examples include B vitamin deficiency, cancer, and genetic disorders such as sickle-cell disease and thalassemia. However, iron deficiency is the most common cause, which is why iron tests are so frequently performed. If iron tests rule out iron deficiency, another source for the anemia must be found. See the article on anemia for more on these.
- What foods contain the most iron?
Heme-iron is the easiest form of iron for the body to absorb. It is found in meats and eggs. Non-heme iron is found in a wide variety of plants and in iron supplements. Iron-rich sources include: green leafy vegetables, (such as spinach, collard greens, and kale), wheat germ, whole grain breads and cereals, raisins, and molasses. If you have been diagnosed with iron deficiency anemia or you are pregnant or breast feeding, vitamin pills or tablets may be needed to provide extra iron. Ask your doctor about the right supplement for you.
- Who needs iron supplements?
The people who typically need iron supplements are pregnant women and those with documented iron deficiency. People should not take iron supplements before talking to their doctor as excess iron can cause chronic iron overload. An overdose of iron pills can be toxic, especially to children.
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
Descriptions of clinical laboratory tests were originally prepared for use on Lab Tests Online, an award-winning patient education website on clinical laboratory testing. Lab Tests Online is produced by the American Association for Clinical Chemistry (AACC), a global scientific and medical professional organization dedicated to clinical laboratory science and its application to healthcare. The Lab Tests Online website is developed in collaboration with other laboratory professional societies and is funded in part through corporate sponsorships.