Anaemia and the Digestive System

Anaemia is a fall in the haemoglobin level below what is expected for a person’s age and sex. Haemoglobin is the protein that allows red blood cells to carry oxygen to the tissues.

Anaemia has many causes. A substantial proportion of them can be related to the stomach and bowel. Unnoticed blood loss from the digestive system, inadequate absorption of iron or vitamins, and certain chronic gastrointestinal diseases can all lead to anaemia.

Iron deficiency anaemia with no explanation in particular should be assessed for an underlying gastrointestinal disease.

Iron deficiency and anaemia have many causes; on their own they do not mean cancer.

What symptoms can anaemia cause?

Symptoms vary with the severity of the anaemia and how quickly it develops.

Common complaints may be:

• Fatigue and tiring easily
• Reduced capacity for exertion
• Shortness of breath
• Palpitations
• Dizziness
• Headache
• Pallor of the skin
• Difficulty concentrating

When anaemia develops slowly the body can partly adapt to it. Some patients therefore have no marked complaint even though the haemoglobin has fallen considerably.

Why does the digestive system cause anaemia?

The gastrointestinal system can cause anaemia by three main mechanisms:

Unnoticed blood loss

Bleeding from the stomach or bowel can be very small in quantity but go on for a long time.

The bleeding may not be visible from the outside. Iron deficiency anaemia can develop over months or years even though the patient has never seen blood in their stool.

Failure to absorb iron and vitamins

Iron, vitamin B12 and folate — substances needed to make blood — are absorbed in the digestive system.

Certain diseases of the stomach or small intestine can impair the absorption of these substances and lead to anaemia.

Chronic disease and inflammation

In chronic inflammatory diseases such as Crohn’s disease and ulcerative colitis, the inflammation itself contributes to the development of anaemia alongside the blood loss.

Why does iron deficiency anaemia matter?

Iron deficiency anaemia is a diagnosis, but it does not on its own explain why the iron is deficient.

Simply giving an iron preparation to someone found to have a low iron and ferritin on a blood test is not enough in some situations.

The important question is this:

Why did the iron become deficient?

Investigating gastrointestinal blood loss matters particularly where iron deficiency anaemia is newly found in adult men and in women after the menopause.

Heavy menstrual bleeding is a common cause in menstruating women, but gastrointestinal causes may also need to be assessed depending on the patient’s characteristics and any accompanying findings.

Which digestive diseases can lead to anaemia?

Diseases of the stomach and duodenum

• Gastric and duodenal ulcers
• Erosive gastritis
• Certain gastric tumours
• Atrophic gastritis
• In some situations, Helicobacter pylori infection

can be associated with chronic blood loss or with disturbance of iron and B12 metabolism.

Diseases of the large bowel

• Colon polyps
• Colorectal cancer
• Inflammatory bowel disease
• Bleeding of vascular origin (angiodysplasia)
• Other bowel lesions that bleed

can cause iron deficiency.

In some right-sided colon tumours in particular, iron deficiency anaemia can be the first finding without any visible bleeding.

That does not mean the cause is colon cancer; it shows why investigation matters in the patients who need it.

Coeliac disease

Iron absorption from the small intestine can be impaired in coeliac disease.

In some patients, iron deficiency anaemia can be the first sign of the disease with no diarrhoea, weight loss or marked gastrointestinal complaint.

Crohn’s disease and ulcerative colitis

In these diseases, blood loss from the bowel, inflammation, malnutrition and deficiencies of certain vitamins can together cause anaemia.

Does vitamin B12 deficiency cause anaemia too?

Yes.

Vitamin B12 deficiency can cause a macrocytic anaemia. Burning of the tongue, numbness, pins and needles, unsteadiness and other neurological symptoms can develop alongside it.

The causes of B12 deficiency include:

• Autoimmune gastritis and pernicious anaemia
• Operations on the stomach
• Crohn’s disease affecting the terminal ileum
• Diseases of the small intestine
• Long-term use of certain medicines

How do you tell that the anaemia is coming from the digestive system?

The first step is to establish the type of anaemia and its cause.

Where it is thought necessary, your doctor may request:

• A full blood count
• Ferritin
• Serum iron and transferrin saturation
• Vitamin B12 and folate
• Reticulocytes
• Markers of inflammation
• Tests for coeliac disease

The gastrointestinal system may then need to be investigated depending on the results and on the patient’s age, sex, complaints and other risk factors.

Are endoscopy and colonoscopy necessary?

Not every patient with anaemia automatically needs endoscopy and colonoscopy.

But in unexplained or recurrent iron deficiency anaemia — particularly in adult men and in women after the menopause — assessment of the gastrointestinal system is often necessary.

Gastroscopy and colonoscopy can be performed depending on the patient’s characteristics.

If no cause is found on these investigations but the iron deficiency persists, the small intestine can also be investigated in selected patients. Capsule endoscopy and other imaging methods can be used for this.

Which findings matter most?

Assessment should not be delayed if anaemia comes with any of the following:

• Blood in the stool
• Black, tarry stools
• Unintentional weight loss
• A newly developed change in bowel habit
• Persistent or recurrent abdominal pain
• Difficulty swallowing
• Recurrent vomiting
• Marked loss of appetite
• Iron deficiency with no explanation
• Anaemia that does not correct with iron treatment, or that returns

Emergency medical assessment may be needed where there is very marked fatigue, fainting, breathlessness at rest, chest pain, severe palpitations or obvious gastrointestinal bleeding.

Is taking iron enough?

Where iron deficiency is found, replacing the iron matters in suitable patients. But the other important part of the treatment is establishing what caused the iron to become deficient.

The haemoglobin correcting with iron treatment does not always show that the underlying cause has gone.

The cause should therefore be investigated particularly in iron deficiency anaemia that is unexplained, recurrent, or that reappears after treatment.

Remember: anaemia can sometimes be the first sign of a disease of the digestive system. In iron deficiency anaemia in particular, what matters is not only replacing the missing iron but establishing why the iron went missing. Rather than reaching your own diagnosis, a gastroenterology assessment should be made where it is needed.