Iron Deficiency Anaemia

The bone marrow requires iron to produce haemoglobin. There are several scenarios where iron stores can be used up and the patient can become iron deficient:

  • Insufficient dietary iron
  • Iron requirements increase (for example in pregnancy)
  • Iron is being lost (for example slow bleeding from a colon cancer)
  • Inadequate iron absorption

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 the acid drops 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.

 

Causes

  • Blood loss is the most common cause in adults
  • Dietary Insufficiency is the most common cause in growing children
  • Poor iron absorption
  • Increased requirements during pregnancy

Whilst growing the dietary requirements of children often exceed their dietary intake, particularly if their diet is low in red meat.

The most common cause in adults in blood loss. In menstruating women, particularly in women with heavy periods (menorrhagia) there is a clear source of blood loss. In women that are not menstruating or men the most common source of blood loss is the gastrointestinal tract. It is important to be suspicious of a GI tract cancer. Oesophagitis and gastritis are the most common causes of GI tract bleeding. Inflammatory bowel disease (Crohn’s and ulcerative colitis) should also be considered.

 

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 saturations. 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 in inflammation, such as with infection or cancer. If ferritin in the blood is low it is highly suggestive of iron deficiency. If ferritin is high then this 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 and if iron levels go up transferrin will be more saturated. It can temporarily increase after eating a meal rich in iron or taking iron supplements so a fasting sample gives the most accurate results.

Blood Test

Normal Range

Serum Ferritin

41 – 400 ug/L

Serum Iron

12 – 30 μmol/L

Total Iron Binding Capacity

45 – 80 μmol/L

Transferrin Saturation

15 – 50%

Two things can increase the values of all of these results giving the impression of iron overload:

  • Supplementation with iron
  • Acute liver damage (lots of iron is stored in the liver)

 

Management

New iron deficiency in an adult without a clear underlying cause (for example heavy menstruation or pregnancy) should be investigated with suspicion. This involves doing a oesophago-gastroduodenoscopy (OGD) and a colonoscopy to look for cancer of the gastrointestinal tract.

Management involves treating the underlying cause and correcting the anaemia. The anaemia can be treated depending on the severity and symptoms with three methods, that range from fastest to slowest and most invasive to least invasive:

  1. Blood transfusion. This will immediately correct the anaemia but not the underlying iron deficiency and also carries risks.
  2. Iron infusion e.g. “cosmofer”. There is a very small risk of anaphylaxis but it quickly corrects the iron deficiency. It should be avoided during sepsis as iron “feeds” bacteria.
  3. Oral iron e.g. ferrous sulfate 200mg three times daily. 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.

When correcting iron deficiency anaemia with iron you can expect the haemoglobin to rise by around 10 grams/litre per week.

 

Last updated April 2019
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