To evaluate your body's current store of iron
Serum iron blood tests are not performed routinely. Most often, serum iron levels are tested if your doctor thinks that you might have too much iron in your blood. A high iron level can be due to a genetic condition, multiple or extensive blood transfusions, or rarely due to ingestion of an overdose of iron (usually in children).
Previously, serum iron was also commonly requested when iron deficiency was suspected. However, it is now recommended that the amount of stored iron (in the form of ferritin) rather than serum iron is measured to aid diagnosis of iron deficiency anaemia. Ferritin analysis gives a measure of body iron stores and is a better indicator of iron deficiency than measuring the iron in blood. However, serum iron blood tests can help to identify when anaemia is due to a long-term (chronic) illness.
A blood sample taken from a vein in your arm
Your doctor may request that you fast for 12 hours prior to some iron blood tests. In this case, only water is permitted. You should not take any iron tablets for 24 hours before the test. Iron is absorbed rapidly from food or tablets, and can make your blood iron levels falsely high.
Iron is an essential nutrient. It is needed in small quantities to help form normal red blood cells (RBCs). Iron is a critical part of haemoglobin, the protein in red blood cells that binds oxygen in the lungs and releases it as blood travels to other parts of the body. Low iron levels can lead to anaemia and the production of RBCs that are small (microcytic) and pale (hypochromic). Large quantities of iron can be toxic to the body, and absorption of too much iron over time can lead to the accumulation of iron compounds in organs and tissues. This can damage organs such as the liver, joints, heart, and pancreas.
Iron is normally absorbed from food in the small intestine and transported throughout the body bound to transferrin, a transport protein produced by the liver. About 70% of the iron transported is incorporated into the haemoglobin inside RBCs. Most of the rest is stored in the tissues as ferritin or haemosiderin. Small amounts of iron are used to produce other proteins such as myoglobin (the oxygen carrying protein in muscle), and some enzymes.
Iron tests evaluate the amount of iron in the body by measuring several substances in the blood. These tests [namely transferrin or TIBC, ferritin-see in detail below] are often requested at the same time and the results considered together to help diagnose and/or monitor iron deficiency or iron overload.
Iron overload may be acute or chronic. Acute iron poisoning may occur, especially in children, with the ingestion of iron tablets. Chronic overload may be due to excessive intake, hereditary haemochromatosis, multiple blood transfusions or several other conditions.
How is it used?
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.
When is it requested?
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
- 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.
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 Iron Deficiency Low High High Low Low Haemochromatosis High Low Low High High Chronic Illness Low Low Low/Normal Low Normal/High Iron Poisoning High Normal Low High Normal
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.
Is there anything else I should know?
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.
Is iron deficiency the same thing as anaemia? What are the symptoms?
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.
Does anaemia due to iron deficiency happen quickly or does it take a long time?
Iron deficiency anaemia comes on gradually. When the rate of iron loss exceeds the amount of iron absorbed from your diet, the first thing that occurs is that iron stores are used up. In this stage, ferritin will be low, but iron and TIBC are usually normal and there is no anaemia. As iron deficiency worsens, blood iron levels fall, TIBC and transferrin rise, and red blood cells may start to become small and pale, but there is still an adequate number of red blood cells. With prolonged or severe iron deficiency, anaemia develops.
What are some causes of anaemia besides iron-deficiency?
Many different conditions can cause anaemia other than iron deficiency. Some examples include Vitamin B12 deficiency, folate deficiency, cancer, and genetic disorders such as sickle-cell disease, thalassemia and pernicious anaemia. 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 anaemia must be found. See the article on Anaemia for more on these.
What are signs of iron overload in my system?
The most common symptom is pain, as iron accumulates in the body, usually in the joints. Other symptoms include fatigue and lack of energy, abdominal pain, loss of sex drive, heart problems and diabetes. Some people, however, have no symptoms of this condition.
What foods contain the most iron?
Haem-iron is the easiest form of iron for the body to absorb. It is found in meats and eggs. Non-haem iron is found in a wide variety of plants and in iron supplements. Iron-rich sources include: dark green leafy vegetables (such as spinach, watercress and curly kale), iron-fortified breads, apricots, raisins, nuts and pulses (beans, peas and lentils). However, the amount of iron that is absorbed in the gut can also be altered by other substances in the diet; Vitamin C can help absorbing iron while tea, coffee and foods with high levels of phytate, such as wholegrain cereals can reduce absorption. If you have been diagnosed with iron deficiency anaemia 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. In some occasions, where oral intake of iron does not improve the iron levels (eg; absorption problems) iron will be given intravenously via a drip. (Through a small tube in to your arm).
My friend told me I can take too much iron - is that right?
Unless you have iron deficiency or eat a very poor diet, you probably don't need extra iron supplements. If you take in much more iron than is recommended, you may develop iron overload, which causes a rise in blood iron and ferritin levels. If you have an inherited disorder called hereditary haemochromatosis, taking extra iron can cause more rapid iron accumulation and possibly accelerate the rate of damage to your organs.
Who needs iron supplements?