The bone marrow requires iron to produce haemoglobin. There are several scenarios where iron stores can be used up and the patient becomes iron deficient:
- Dietary insufficiency. This is the most common cause in children.
- Loss of iron, for example in heavy menstruation
- Inadequate iron absorption, for example in Crohn’s disease
Iron is mainly absorbed in the duodenum and jejunum. It requires the acid from the stomach to keep the iron in the soluble ferrous (Fe2+) form. When there is less acid in the stomach, it changes to the insoluble ferric (Fe3+) form. Therefore, medications that reduce the stomach acid, such as proton pump inhibitors (lansoprazole and omeprazole) can interfere with iron absorption. Conditions that result in inflammation of the duodenum or jejunum such as coeliac disease or Crohn’s disease can also cause inadequate iron absorption.
Understanding Tests for Iron Deficiency
Iron travels around the blood as ferric ions (Fe3+) bound to a carrier protein called transferrin. Total iron binding capacity (TIBC) basically means the total space on the transferrin molecules for the iron to bind. Therefore, total iron binding capacity is directly related to the amount of transferrin in the blood. If you measure iron in the blood and then measure the total iron binding capacity of that blood, you can calculate the proportion of the transferrin molecules that are bound to iron. This is called the transferrin saturation. It is expressed as a percentage. The formula is:
Transferrin Saturation = Serum Iron / Total Iron Binding Capacity
Ferritin is the form that iron takes when it is deposited and stored in cells. Extra ferritin is released from cells when there is inflammation, such as with infection or cancer. If ferritin in the blood is low, this is highly suggestive of iron deficiency. High ferritin is difficult to interpret and is likely to be related to inflammation rather than iron overload. A patient with a normal ferritin can still have iron deficiency anaemia, particularly if they have reasons to have a raised ferritin, such as infection.
Serum iron varies significantly throughout the day, with higher levels in the morning and after eating iron containing meals. On its own serum iron is not a very useful measure.
Total iron binding capacity can be used as a marker for how much transferrin is in the blood. It is an easier test to perform than measuring transferrin. Both TIBC and transferrin levels increase in iron deficiency and decrease in iron overload.
Transferrin saturation gives a good indication of the total iron in the body. In normal adults it is around 30%, however if there is less iron in the body, transferrin will be less saturated. When iron levels go up, transferrin will be more saturated. It can increase shortly after eating a meal rich in iron or taking iron supplements, so a fasting sample is better.
|
Blood Test |
Normal Range |
|
Serum Ferritin |
12 – 200 ug/L |
|
Serum Iron |
14 – 31 μmol/L |
|
Total Iron Binding Capacity |
54 – 75 μmol/L |
Two things can increase the values of all of these results (except TIBC, which will be low), giving the impression of iron overload:
- Supplementation with iron
- Acute liver damage (lots of iron is stored in the liver)
Management
Management involves treating the underlying cause and correcting the anaemia. In children the underlying cause is usually dietary deficiency, so input from a dietician can be helpful.
Iron can be supplemented with ferrous sulphate or ferrous fumarate. This slowly corrects the iron deficiency. Oral iron causes constipation and black coloured stools. It is unsuitable where malabsorption is the cause of the anaemia.
Blood transfusions are very rarely necessary. Children are generally able to tolerate a low haemoglobin well and can be given time to correct their anaemia.
Last updated January 2020