Normal hemoglobin levels
Women: 120-160 g/L
Men: 140-180 g/L

Almost 99% of all blood cells are red blood cells. A protein called hemoglobin in the red blood cells carries oxygen to tissues of the body. Hemoglobin is rich in iron. Its role is to carry oxygen from the lungs to the various parts of the body and to collect the carbon dioxide for elimination through respiration.

When the red blood cell count drops below what is considered normal or "healthy", the person is said to be anemic. Anemia is a decrease in hemoglobin, which can occur for a variety of reasons. A blood test shows the number of red blood cells and your body's hemoglobin levels, and will confirm if you are anemic or not.

In a healthy body, when the number of red blood cells decreases and the level of oxygen in the blood drops, the kidneys secrete a hormone called erythropoietin. This hormone sends a message to the bone marrow (located inside the bone) to produce more red blood cells.

If you have cancer:

1. Your kidneys may not be able to produce enough erythropoietin to stimulate the production of more red blood cells.
2. Your body may have difficulty producing red blood cells. This is because the bone marrow may not be able to respond fully to the signal from the erythropoietin to make more red blood cells.
3. There may be increased loss or destruction of red blood cells. Some types of cancer can cause bleeding which will decrease the number of red blood cells.

In addition to red blood cells, blood is made up of white blood cells and platelets.

White blood cells are the soldiers that defend the body against germs, viruses and bacteria. Neutrophils are the most common type of white blood cell and help the body to fight infection.

When bleeding occurs, the platelets join together and help a blood clot to form to act as a barrier and help stop the bleeding.

A complete blood count (CBC) is one type of blood test typically ordered to ensure the levels of the different types of cells in the blood are within normal ranges. A CBC is a relatively fast and painless procedure requiring less than a drop of blood.

A CBC will measure:

• the number of red blood cells in the blood;
• the amount of hemoglobin (the protein in red blood cells that carries oxygen);
• the percentage of red blood cells in the blood (called the hematocrit);
• the number of white blood cells in the blood and the percentages of the individual types of white blood cells;
• the number of platelets in the blood.

The doctor may also test to see the amount of iron in the blood. Depending upon the type of cancer you have, your blood might be tested for other proteins or substances.

Throughout your illness - and particularly when undergoing chemotherapy -- your doctor will monitor the levels of red blood cells, hemoglobin, iron, white blood cells and platelets in your blood. Talk with your doctor about your blood count and what it means.

Click here to take a short hemoglobin quiz. You will need to know your hemoglobin level.