Reviewed by: HU Medical Review Board | Last Reviewed: January 2018.

If you have anemia, your blood does not carry enough oxygen throughout your body.1 In people with inflammatory bowel disease, anemia is the most common complication to occur outside of the digestive tract.2 In many cases, the cause of anemia is not having enough iron. However, not having enough vitamin B12 or folate (folic acid) can also cause anemia.1

About 60% to 80% of people with inflammatory bowel disease are iron deficient.3 About one-third have such low iron that they are anemic. Patients in the hospital are much more likely to be anemic than outpatients.3 Children are more likely than adults to have iron-deficiency anemia.

Why is inflammatory bowel disease linked with anemia?

There are several reasons why people with inflammatory bowel diseases like Crohn’s disease and ulcerative colitis have iron-deficiency anemia. People with IBD may be losing blood through ulcers on the digestive tract lining, or they may have trouble absorbing iron from foods because of inflammation or surgery. Another cause of low iron is that the diet doesn't contain enough iron-rich foods.3

People with Crohn's disease may be at greater risk of anemia due to low levels of vitamin B12 or folate.4 These vitamins are normally absorbed in the small intestine, which can become inflamed by Crohn's disease. About 20% of people with Crohn’s disease have low levels of vitamin B12.5 You are at greater risk of B12 deficiency if the last section of your small intestine (ileum) was surgically removed.5 Between 4% and 28% of people with Crohn’s disease have low levels of folate.5 Poor diet or difficulty absorbing nutrients can cause folate deficiency. Certain medications used to treat Crohn’s disease also cause a folate deficiency. Examples include sulfasalazine, thiopurines, and methotrexate.3,5,6

What are symptoms of anemia?

If your blood cells are not able to carry enough oxygen throughout the body, you may feel less energetic and unable to do your normal activities. Other symptoms of anemia include paleness, dizziness, fast heart rate, cold hands and feet, breathlessness, and headache. Iron-deficiency anemia can also lead to hair loss, brittle nails, and restless legs syndrome.3,7

What other conditions can cause anemia?

Many conditions besides inflammatory bowel disease can cause anemia.7 These include:

  • Blood loss because of stomach ulcers or heavy periods.
  • Celiac disease.
  • Interaction with medications.
  • Pregnancy.
  • Genetic diseases.
  • Diet low in iron or very high in calcium.

How is anemia evaluated?

Your health care will do a blood test to check:

  • How much hemoglobin you have. Hemoglobin is an iron-rich protein in red blood cells. It binds with oxygen so that oxygen can travel through the blood.
  • What size your red blood cells are. This is called the mean corpuscular volume.
  • What percentage of your blood is made of red blood cells. This is called the hematocrit.
  • How much hemoglobin there is per red blood cell.

This information tells your health care provider what the cause of anemia is. Your provider may also want do to additional tests. There is a test that checks your iron stores (serum ferritin). Another test evaluates how much iron is actually being transported through your body (transferrin saturation or total iron-binding capacity).3,6 A reticulocyte count measures how many young red blood cells are in your blood. This indicates whether your bone marrow is working correctly. Your provider may look at the red blood cells under a microscope to see what color they are.

How is anemia treated?

If you have iron-deficiency anemia, your health care provider will probably recommend an iron supplement. Many people can take iron supplements by mouth. Oral iron supplements do cause side effects. Common side effects are constipation, nausea, or stomach irritation.3

Alternatively, your health care provider may recommend an intravenous (IV) iron supplement. This supplement is administered directly into your vein.3 Some people may start with an IV iron supplement. Other people may need IV iron because oral iron was not enough.

If IV iron does not treat your anemia, your provider may prescribe medications called erythropoiesis stimulating agents.3 These medications cause your bone marrow to make more red blood cells.

Anemia re-occurs in more than half of patients with inflammatory bowel disease.3 For this reason, your health care provider may recommend some type of ongoing treatment.

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