Your doctor may monitor your blood cell counts carefully during your cancer treatment. There's a good reason you're having your blood drawn so often — low blood cell counts put you at risk of serious complications.

If you're undergoing certain cancer treatments that could cause low blood cell counts, your doctor will likely monitor your blood cell counts regularly using a test called a complete blood count with differential (CBC w/diff). Low blood cell counts are detected by examining a blood sample taken from a vein in your arm.

When checking your blood cell count, your doctor is looking at the numbers and types of the following:

• White blood cells. White blood cells help your body fight infection. The CBC w/diff test measures the levels of five types of white blood cells in your blood. Your doctor will pay close attention to the levels of neutrophils, which are particularly helpful for fighting infections caused by bacteria. A low neutrophil count (neutropenia) leaves your body more open to infection. And if an infection does develop, your body may be unable to fight it off.
• Red blood cells. Red blood cells carry oxygen throughout your body. Your red blood cells' ability to carry oxygen is measured by the amount of hemoglobin in your blood. If your level of hemoglobin is low, you're anemic and your body works much harder to supply oxygen to your tissues. This can make you feel fatigued and short of breath.
• Platelets. Platelets help your blood to clot. A low platelet count (thrombocytopenia) means your body can't stop itself from bleeding.

Common cancer-related causes of low blood cell counts include:

• Chemotherapy. Certain chemotherapy drugs can damage your bone marrow — the spongy material found in your bones. Your bone marrow makes blood cells, which grow rapidly, making them very sensitive to the effects of chemotherapy. Chemotherapy kills many of the cells in your bone marrow, but the cells recover with time. Your doctor can tell you whether your specific chemotherapy treatment and dose will put you at risk of low blood cell counts.
• Radiation therapy. If you receive radiation therapy to large areas of your body and especially to the large bones that contain the most bone marrow, such as your pelvis, legs and torso, you might experience low levels of red and white blood cells.
• Cancers of the blood and bone marrow. Blood and bone marrow cancers, such as leukemia, grow in the bone marrow and don't allow normal blood cells to develop.
• Cancers that spread (metastasize). Cancer cells that break off from a tumor can spread to other parts of your body, including your bone marrow. The cancerous cells can displace other cells in your bone marrow, making it difficult for your bone marrow to produce the blood cells your body needs.

Low blood cell counts may delay your next round of treatment or lead your doctor to reduce medication dosage or prescribe a new medication. Monitoring your blood cell counts allows your doctor to prevent or reduce your risk of complications.

The most serious complications of low blood cell counts include:

• Infection. With a low white blood cell count and, in particular, a low level of neutrophils, you're at higher risk of developing an infection. And if you develop an infection when you have a low white blood cell count, your body can't protect itself. Infection can lead to death in severe cases.

  Even a mild infection can delay your chemotherapy treatment, since your doctor may wait until your infection is cleared and your blood cell counts go back up before you continue. Your doctor may also recommend medication to increase your body's production of white blood cells.

• Anemia. A low red blood cell count is anemia. The most common symptoms of anemia are fatigue and shortness of breath. In some cases, fatigue becomes so severe that you must temporarily halt your cancer treatment or reduce the dose you receive. While mild anemia is common and often does not cause fatigue, tell your doctor if you are having these symptoms to see if anemia is a possible cause.

  Anemia can be relieved with a blood transfusion or with medication to increase your body's production of red blood cells.

• Bleeding. Low numbers of platelets in your blood can cause bleeding. You might bleed excessively from a small cut or bleed spontaneously from your nose or gums. Rarely, dangerous internal bleeding can occur.

  A low platelet count can delay your treatment. You may have to wait until your platelet levels go up in order to continue with chemotherapy or to have surgery. A low platelet count can also be treated with a platelet transfusion.

Unless your blood cell counts are very low, you probably won't experience any signs or symptoms and you won't be able to tell that your blood cell counts are down. That's why your doctor may order frequent blood tests to follow your blood cell counts.

Ask your doctor whether your cancer treatment is likely to cause low blood cell counts and what signs and symptoms you should be looking for. If you notice any signs or symptoms of low blood cell counts, tell your doctor right away.

Take steps to keep your body healthy when you have low blood cell counts. For example:

• Eat a balanced diet. Your body needs all the vitamins and nutrients it can get to heal itself during and after your treatment. Choose plenty of fruits and vegetables. If treatment complications make eating difficult — for example, if you experience nausea and vomiting or mouth sores — experiment to find foods you can tolerate.
• Avoid injury. Many everyday activities put you at risk of cuts and scrapes. A low platelet count makes even minor abrasions serious. A low white blood cell count can turn a small cut into a starting point for a serious infection. Use an electric shaver rather than a razor to avoid nicks. Ask someone else to cut up food in the kitchen. Be gentle when brushing your teeth and blowing your nose.
• Avoid germs. Avoid unnecessary exposure to germs when you can. Wash your hands frequently or use a liquid hand sanitizer. Avoid people who are sick and stay away from crowds. Have someone else clean the litter box, bird cage or fish tank. Don't eat raw meat or eggs.

Talk to your health care team about other ways you can cope with low blood cell counts.