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. Testing may include:

• Serum iron - measures the concentration of iron in the blood. The amount of iron within the blood varies throughout the day, and from one day to the next. An blood (serum) iron test is therefore not a useful measure of iron status if it is used on its own unless iron overdose is suspected. Serum iron is therefore often requested in combination with other tests of iron status. Such tests include transferrin saturation, ferritin, TIBC (total iron binding capacity) and UIBC (unbound iron binding capacity).
• Transferrin or TIBC (total iron binding capacity). A laboratory will often measure one of either TIBC or transferrin. Transferrin is the main transport protein to which iron is bound in the blood. TIBC is a measure of all the proteins in the blood that are available to bind with iron (including transferrin). The TIBC test is a good indirect measurement of transferrin, as transferrin is the primary iron-binding protein. 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.
• A few laboratories measure the portion of transferrin that has not yet been saturated with iron. UIBC also reflects transferrin levels.
• Transferrin saturation - this is a calculation that represents the percentage of transferrin that is saturated with iron. It can be calculated using either the transferrin or TIBC value, when the serum iron concentration is known
• Serum ferritin - reflects the amount of stored iron in your body; ferritin is the main storage protein for iron inside of cells. It is the most useful indicator of iron deficiency, as the ferritin stores can be significantly decreased before any fall in the serum iron concentration occurs.

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:

• Chronic fatigue/tiredness
• Shortness of breath and dizziness
• Weakness
• Headaches
• Leg pains
• Noticeable heartbeats (palpitations)
• If the anaemia is severe, angina (chest pain)

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 (see below) 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:

• Unexplained joint and muscle pain
• Fatigue, weakness
• Abdominal pain
• Loss of sex drive, impotence, infertility or loss of menstrual periods
• Signs of liver disease, diabetes and / or heart problems
• Heart failure, liver failure

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

The following tests can be used to help recognise problems with iron status.

• Haemoglobin and Haematocrit - These tests are performed as part of a Full Blood Count (FBC). A low value for either test indicates that a person has anaemia. Iron deficiency is a very common cause of anaemia. The average size of red cells (Mean Cell Volume or MCV) and the average amount of haemoglobin in red cells (Mean Cell Haemoglobin or MCH) are also measured in an FBC. In iron deficiency, insufficient haemoglobin is made, causing the red blood cells to be smaller and paler than normal. Both MCV and MCH are low.
• Blood film/picture- this test looks at the size and shape of red blood cells under a microscope. This helps to differentiate iron deficiency anaemia from other different types of anaemias.
• HFE gene test - Haemochromatosis is a genetic disease 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 can be absorbed and excess iron is deposited in many different organs, where it can cause damage and organ failure. The HFE gene test determines whether a person has the mutations that cause the disease. The most common mutation is called C282Y. Not everyone with this genetic mutation will develop haemochromatosis.
• Zinc Protoporphyrin (ZPP) - Protoporphyrin is the precursor to the part of haemoglobin (haem) 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. Sometimes ZPP (and its ratio to haem levels) is used as an early indicator of iron deficiency in children. However, the test is not specific for iron deficiency, and elevated values must be confirmed by other tests. The test is therefore rarely used in the UK, but still has a role in developing countries.
• Additional procedures such as testing the stool for blood (faecal occult blood [FOB] or faecal immunochemical test [FIT]), or endoscopy and colonoscopy may be used to find the cause of anaemia in cases of chronic bleeding from gut. Pelvic ultrasound scans are also used in women to look for the cause of excess menstrual bleeding.
• Liver function tests- This panel of tests may help identify liver damage in iron over load conditions.
• Liver biopsy- If liver damage is suspected following iron overload, a sample of tissue from the liver is removed, using a thin needle. The sample is sent to a laboratory to be checked for the presence of iron as well as for evidence of liver damage, especially scarring or cirrhosis.

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 30s or 40s. 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 people who abuse alcohol 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, long term usage of nonsteroidal anti-inflammatory drugs [NSAIDs] such as Ibuprofen or Aspirin) or women with heavy menstrual periods will lose more iron than normal and can develop iron deficiency. Iron from food is absorbed into the bloodstream in the small intestine. An intestinal disorder, such as celiac disease, which affects the intestine's ability to absorb nutrients from digested food, can lead to iron deficiency anemia. Women who are pregnant or breast feeding supply 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.

Samples for iron should be taken in the morning, before you have had any food to eat. You should not take any iron pills or tablets for 24 hours before the test. Iron is absorbed rapidly from food or pills, and can make your blood iron levels falsely high.

Substances that can cause high iron levels include the contraceptive pill, oestrogen pills and preparations, iron supplements, heavy intake of alcoholic drinks, methyldopa, and chloramphenicol.

Substances that can cause your iron level to be decreased include ACTH (a hormone), the drugs colchicine, desferrioxamine, methicillin, and testosterone.

Iron deficiency refers to a decrease in the amount of iron stored in the body, while anaemia refers to a drop in the number of red blood cells (RBCs) and/or the amount of haemoglobin within the RBCs. It typically takes several weeks after iron stores are depleted for the level of haemoglobin and production of RBCs to be affected and for anaemia to develop. There are usually few symptoms in the early stages of iron deficiency. However, as the condition worsens levels of haemoglobin and RBCs decrease, and ongoing weakness and fatigue can develop. Relatively mild iron deficiency, which may cause no effects at all, is referred to as ‘iron depletion’. If a person is otherwise healthy, symptoms seldom appear before the haemoglobin in the blood drops below a certain level (100g per litre).

As the iron levels continue to be depleted further symptoms of the anaemia may develop such as shortness of breath and dizziness. If the anaemia is severe then chest pain, headaches, fast heartbeat and leg pains may occur. Children may develop learning (cognitive) disabilities. Besides the general symptoms of anaemia, certain symptoms are characteristic of long-term iron deficiency. These include pica (cravings for specific substances, such as liquorice, 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.