The main forms of anaemia caused by GI pathology are:

• Iron deficiency anaemia (IDA)
• Vitamin B12 deficiency
• Anaemia of chronic disease

Iron deficiency anaemia

IDA is by far the most important of these three. In the absence of heavy vaginal bleeding, IDA is almost always assumed to be due to a gastro-intestinal cause. This may be as a result of reduced absorption of dietary iron or increased loss of blood from the gastro-intestinal tract (see Gastro-intestinal bleeding).

It is usually recommended that iron deficiency anaemia is investigated if there is no obvious other cause e.g. poor diet, heavy vaginal bleeding. Most causes of gastro-intestinal blood loss are reversible, so a treatable cause should be sought. The greatest concern, particularly in older patients, is that IDA may be the first manifestation of gastro-intestinal tract cancer.

Vitamin B12 deficiency

Vitamin B12 deficiency is important as it may cause irreversible neurological damage. Deficiency symptoms usually only arise approximately 2 years after the onset of disease, as your body has stores that will last for approximately this length of time.

Vitamin B12 deficiency can be caused by disorders of both the stomach and ileum (the last part of the small bowel). In the absence of disease, vitamin B12 seldom occurs in individuals eating a balanced diet. However, strict vegans are at risk due to reduced dietary intake.

When vitamin B12 deficiency is caused by disease states, it is necessary to supplement these individuals with intramuscular injections of vitamin B12. This therapy is usually life-long.

Anaemia of chronic disease

This condition exists in disease states where there is chronic inflammation that prevents utilization of the body's iron stores, resulting in anaemia. Inflammatory bowel disease is a gastro-intestinal disorder that may cause this.