Iron deficiency anemia

by Rosemarie Tremblay-LeMay MD FRCPC
November 18, 2023

Iron deficiency anemia is a type of anemia caused by low levels of iron in the body. It is the most common cause of anemia among adults. Common causes of iron deficiency anemia include blood loss, pregnancy, and a diet low in iron.

What is anemia?

Anemia means a decreased amount of hemoglobin in the blood. Hemoglobin is a protein that carries oxygen from the lungs to the body and carbon dioxide from the body back to the lungs. It is made and stored in red blood cells (RBCs). Anemia can be caused by a decrease in the number of RBCs in your blood or a decrease in the amount of hemoglobin in each RBC. Because the body uses oxygen to make energy, a person with anemia has less oxygen in their blood which can make them feel tired or short of breath.

What causes iron deficiency anemia?

Under normal conditions, the body gets all of the iron it needs to make new RBCs from a combination of recycled iron (from RBCs after they die) and iron from the diet.  If iron levels in the body are low, new iron can be released from food in the stomach and then absorbed in the intestine. A specialized protein called transferrin is used to carry iron from recycled RBCs and absorbed in the small intestine to areas of the body where iron is needed. In this way, the amount of iron in the body is carefully controlled.

However, any condition that causes the body to lose RBCs or reduces the amount of new iron absorbed from food can lead to iron deficiency.

Common causes of iron deficiency anemia include:

  • Blood loss – This can result from menstrual bleeding, bleeding from the gastrointestinal tract, or an injury that results in significant bleeding.
  • Pregnancy – Unborn babies receive iron from their mothers. For this reason, expecting mothers need extra iron in their diet to make up for this increased demand.
  • A diet low in iron – It is important to eat a diet that contains at least some iron-rich foods. Good sources of iron include meat, fish, and whole-grain cereals. Vitamin C can help increase iron absorption. Eating a diet low in iron will eventually cause anemia of iron deficiency.
  • Reduced absorption of iron in the gastrointestinal tract – Iron from food is absorbed primarily in the small intestine. Any condition that prevents the small intestine from working normally can decrease the amount of iron absorbed into the body. Conditions associated with reduced absorption are celiac disease, intestinal parasites, surgeries of the stomach or small intestine, and inflammatory diseases of the intestine like Crohn’s disease.

How does iron deficiency lead to anemia?

When iron levels are low, developing RBCs in the bone marrow are unable to make enough hemoglobin. As a result, the new RBCs will be smaller (microcytic) and paler (hypochromic) than normal RBCs. The cells also tend to vary in shape compared to normal RBCs which are more uniform. These changes take time to develop and may not be seen at the early stages of iron deficiency.

Iron deficiency anemia

How do doctors test for iron deficiency?

A blood test is the most common way to test for iron deficiency. The blood test will measure both the amount of iron in your blood and the proteins that regulate iron levels.

  • Ferritin – The level of ferritin in the blood provides a good estimate of the amount of iron stored in the body. Ferritin will be decreased in iron deficiency.
  • Iron – This measures the amount of iron in the blood. Although the amount of iron in the blood is decreased in iron deficiency, this test is not especially useful on its own because the levels vary a lot throughout the day and can be decreased for reasons other than iron deficiency.
  • Total iron-binding capacity (TIBC) – This measures how much transferrin protein is available to hold iron. In iron deficiency, less iron is attached to transferrin so the TIBC will be increased.
  • Transferrin saturation – This value represents the amount of iron in the blood divided by the TIBC, shown as a percentage. The transferrin saturation is decreased in iron deficiency.

Iron deficiency can also be diagnosed after a small sample of bone marrow is removed in a procedure called a bone marrow aspirate. The tissue sample is then examined under a microscope by a pathologist using special stains to look at the amount of iron in the tissue sample. Usually, this is not necessary to make the diagnosis since the blood tests can provide an answer.

About this article

This article was written by doctors to help you read and understand your pathology report. Contact us if you have any questions about this article or your pathology report. Read this article for a more general introduction to the parts of a typical pathology report.

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