Iron Tests

Iron status may be evaluated by requesting one or more tests to determine the amount of iron in the blood, the capacity of the blood to transport iron, and the amount of iron in storage. They may also help differentiate various causes of anaemia. Testing may include:

A number of these tests may be requested together to help the doctor determine the cause of iron deficiency and/or overload.

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

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

Tests for iron, ferritin, transferrin saturation, and a transferrin or TIBC may be requested when a doctor suspects that a person may have a chronic iron overload. In the absence of a history of multiple transfusions, the most common cause of iron overload is a genetic condition called hereditary haemochromatosis. HFE genetic testing may be requested to help confirm a diagnosis of hereditary haemochromatosis and sometimes when a person has a family history of haemochromatosis.

The signs and symptoms of iron overload are as follows:

When a child is suspected to have ingested iron tablets, a serum iron test is requested 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.

Iron deficiency can range in severity. The mildest stage is iron depletion, which means the amount of functioning iron in the body is adequate, but the body does not have any extra iron stores. Serum iron concentration may be normal in this stage, but ferritin levels will be low. As iron deficiency worsens, all of the stored iron is used and the body begins to produce more transferrin to increase iron transport. Serum iron becomes low, and transferrin and TIBC are high. As this stage progresses, fewer red cells are produced. In iron-deficiency anaemia, the number of red cells is decreased and many of the cells appear smaller and paler than normal.

Iron overload may be acute or chronic. Acute iron overload is suspected if the iron level is high but TIBC and ferritin are normal. If the person has a clinical history consistent with iron overdose, then iron poisoning is the most likely diagnosis. Iron poisoning occurs when a large amount of iron is taken all at once. While this is rare, it most commonly occurs in children who ingest their parents' iron supplements. In some cases, iron poisoning can be fatal.

Chronic iron overload can occur due to a genetic condition called hereditary haemochromatosis, following multiple blood transfusions or due to other conditions such as liver disease. Hereditary haemochromatosis occurs in persons with two genetic mutations of the HFE gene. The most common mutation is known as C282Y. However, many people who have this genetic mutation will not develop 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 multiple transfusions, such as may happen with thalassemia or other forms of anaemia. The iron from each transfused unit of blood stays in the body, eventually causing a large build up in the tissues. Some alcoholics with chronic liver disease may also develop iron overload.

Normal iron concentrations 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, deficiency will eventually develop. Unless a person has a poor diet, there is usually enough iron to prevent iron deficiency and/or iron deficiency anaemia in healthy people. In certain situations, there is an increased need for iron. Persons with chronic bleeding from the gut (usually from ulcers or tumours) 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 despite sufficient iron stores. In many chronic diseases, especially cancers, autoimmune diseases, and chronic infections (including AIDS), the body cannot properly use iron to make more red cells, and so an anaemia develops. This disorder is known as “functional iron deficiency” or “anaemia of chronic disease”. The blood tests in persons with this condition will normally show low levels of serum iron and transferrin but normal or even high ferritin levels.