“In biology, nothing is clear, everything is too complicated, everything is a mess, and just when you think you understand something, you peel off a layer and find deeper complications beneath. Nature is anything but simple.” Richard Preston


What is anaemia? Anaemia is a condition where there are not enough circulating red blood cells. Haemoglobin is the substance within red cells that gives them their colour and also carries oxygen to transport it around the body. The red cells are made in the bone marrow.

What are the symptoms of anaemia? Mild anaemia may be detected coincidentally on blood tests and not cause any symptoms. Even severe anaemia, if it develops very gradually may come as a surprise to patients who have learnt to cope with the symptoms. Anaemia can cause feelings of weakness, shortness of breath and fatigue, as well as making someone look pale. The condition that causes anaemia may also cause additional symptoms as well as those due to the anaemia.

What are the different types of anaemia? There are many different causes of anaemia that lead to different types of the condition. These types are generally distinguished initially on the basis of the size of the red cells and how much haemoglobin they contain. Some causes of anaemia also affect other blood cells that are made in the bone marrow (such as white cells and platelets).

Which types of anaemia are related to the gastrointestinal tract? A very common form of anaemia due to deficiency of iron affects 5-10% of the population at any time. Iron is essential for making blood, and blood contains so much iron that it causes the metallic taste of blood. If blood is lost in large amounts - or even tiny amounts on a regular basis - then the resulting deficiency of iron makes it difficult for the bone marrow to make more to catch up with with correct amount. In iron deficiency anaemia, the red cells are small. Other substances are essential for making blood and deficiency of Vitamin B12 or Folic acid lead to a type of anaemia with large red cells. Vitamin B12 deficiency can be caused by diet (it is only present in food derived from animal sources) or malabsorption in the intestine; folic acid deficiency can also be due to diet (although it is present in vegetables and enriched in bread and breakfast cereals). A form of anaemia with normal sized red cells is often due to inflammation, which can be present anywhere including the gastrointestinal tract.

What are the causes of iron deficiency? Iron deficiency anaemia is commonest in females due to the regular monthly loss of blood in menses. If periods are not heavy or absent and there is no other obvious cause of iron deficiency, then it is usual for gastroenterologists to investigate the cause as the gastrointestinal tract is then the commonest site for hidden blood loss. This can be due to inflammation or ulcers in the stomach, damage to the lining of the intestine due to medications (such as NSAIDs - see 'peptic ulcer') or fragile blood vessels in the stomach or intestine. In the colon, polyps and fragile blood vessels are common causes. Cancers at any site - most commonly the colon, but also in the stomach and very rarely the small intestine - also lead to gradual blood loss and iron deficiency.
Iron deficiency can also be due to insufficient iron intake in the diet (particularly in vegetarians), or lack of absorption of iron due to Coeliac disease or autoimmune gastritis.

What investigations are required to investigate iron deficiency anaemia? In order to locate a gastrointestinal cause of anaemia, it is standard to carry out a gastroscopy and a colonoscopy. These will help to rule out cancers, coeliac disease, peptic ulcers or colonic polyps as a cause. If no cause is found, it is sometimes necessary to carry out a video capsule enteroscopy or an abdominal CT-scan (X-ray test).

Where can I get more information? The NHS website is a good starting place for more information on iron deficiency, with links to other sites.

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