Ferritin

What is being analysed?
Ferritin is the main iron storage protein, and its plasma concentration directly reflects the size of the body’s iron stores.

Iron is stored mainly in complexes with ferritin and, to a lesser extent, as haemosiderin; both are stored mainly in the liver, bone marrow and spleen, but small amounts of ferritin are found in the bloodstream in balance with the tissue stores.

When the amount of available iron starts to fall, the ferritin stores, and therefore the iron bound to them, are mobilised before a true deficiency develops.

How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?

How is it used?
The ferritin test is requested to assess the size of the body’s iron reserves. A more detailed study of iron metabolism also requires serum iron and transferrin or total iron-binding capacity (TIBC).

When is it requested?
Iron deficiency anaemia can easily be identified with a full blood count showing low haemoglobin and haematocrit, with small, pale (microcytic and hypochromic) red blood cells. In this case, to confirm the diagnosis, ferritin may also be requested, together with other tests such as serum iron and transferrin.

The ferritin test may also be carried out when there is iron overload, as after repeated transfusions or in haemochromatosis.

What does the test result mean?
Ferritin levels are generally below the reference limit in iron deficiency, whose most common cause is increased loss or need (heavy periods, bleeding in the gut, pregnancy) rather than reduced dietary intake; more rarely, low ferritin occurs with severe depletion of plasma proteins, as in malnutrition.

Ferritin levels, on the other hand, may be well above the reference limit when iron builds up chronically, as in haemochromatosis.

Is there anything else I should know?
Ferritin is an intracellular protein and only small amounts are found in the blood; when one of the organs that store large amounts of it (mainly the liver, spleen and bone marrow) is damaged, blood ferritin may rise because of the tissue damage even if the body has enough iron. The ferritin test is of limited use in patients with liver disease, chronic infections, cancer and autoimmune diseases.

1. Does “iron deficiency” mean anaemia? What are the symptoms of iron deficiency?
2. What are the clinical signs of iron overload?
3. Which foods contain the most iron?
4. Is it possible to take in more iron from the diet than the body needs?
5. How long does it take for iron deficiency to develop into clinically evident anaemia?

1. Does “iron deficiency” mean anaemia? What are the symptoms of iron deficiency?
Iron deficiency anaemia is the most clinically significant form of iron deficiency, but iron deficiency alone may have no clinical consequences and does not necessarily develop into anaemia. In iron deficiency, the ferritin iron in the stores is used first; once the stores are empty, circulating iron is taken from transferrin; then the production of iron-containing enzymes falls, and only at the end does haemoglobin production fall, causing anaemia. Biochemically, this shows up as a fall in serum iron and ferritin, with normal or slightly raised TIBC and transferrin saturation below 20%, without any blood count abnormalities. As the iron deficiency worsens, haemoglobin may fall, leading to clinically evident anaemia, while the biochemical changes of the previous stage remain; red blood cells are produced without enough haemoglobin being made, so typically small, pale (microcytic and hypochromic) red blood cells are produced. Iron deficiency is often clinically silent, and progression to symptoms is extremely slow; clinical signs such as weakness, pallor, rapid heartbeat, irritability and insomnia appear only when anaemia develops.

As well as the general symptoms of anaemia, when iron deficiency lasts a long time other symptoms may appear, such as a burning sensation and smoothness of the tongue, cracks at the corners of the mouth and spoon-shaped nails.

2. What are the clinical signs of iron overload?
The most common symptom is joint pain. Other symptoms include weakness, abdominal pain, bronze-coloured skin and loss of libido. However, some cases have no symptoms at all.

3. Which foods contain the most iron?
An iron-rich diet includes lean meat, liver, eggs, green leafy vegetables such as spinach, wheat germ, and wholegrain cereals and starchy foods. When the need for iron is higher, as in iron deficiency anaemia, pregnancy, breastfeeding and adolescence, dietary iron intake can be increased; dietary changes are the first treatment, although their effectiveness depends on how severe the iron deficiency is. Unless iron deficiency has been confirmed, nutritional support is not needed.

4. Is it possible to take in more iron from the diet than the body needs?
There is a condition known as “haemosiderosis”, characterised by a build-up of iron that can be identified by a marked increase in serum iron and ferritin; this condition can only be caused by repeated transfusions or poisoning, not by a normal diet. In haemochromatosis, an inherited disease characterised by iron build-up mainly in the liver, heart and pancreas, excess iron in the diet can speed up tissue damage.

5. How long does it take for iron deficiency to develop into clinically evident anaemia?
Iron deficiency anaemia develops very slowly. When iron losses exceed absorption from the gut, the body draws on its cell reserves. At this stage ferritin may be low, but serum iron and TIBC are generally normal and there are no clinical signs of anaemia. If the iron deficiency persists, serum iron falls while TIBC and transferrin rise; at the same time abnormalities appear in the full blood count, with small, pale red blood cells, although still in sufficient numbers. Clinically evident anaemia appears only after iron deficiency has persisted for long periods.