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When you have cancer, your health care team will monitor your blood counts with regular blood tests. A low white blood cell count (or low WBC count) can be a sign of a lowered level of immunity or immunosuppression, which can be caused by certain disease such as cancer, or by cancer treatments such as chemotherapy or radiation therapy. A low white blood cell count is sometimes called neutropenia.
Neutropenia means your white blood cell (WBC) count is lower than the normal range on a blood test. It’s called neutropenia because the blood cells being counted are a specific type of WBC called a neutrophil. When your neutrophil count is low, your body will have a harder time fighting infections. Neutropenia might also be called having a low ANC or a low absolute neutrophil count based on your blood test results.
White blood cells are part of the immune system. There are different types of white blood cells, and they each have a key role in the body’s defense against germs:
A Complete Blood Count test (CBC) will usually show your total WBC count, but it might also show more detailed counts for some specific types of WBCs.
Neutrophils form a very important defense against most types of infection. Normally, most of our white blood cells are neutrophils. In patients with cancer, neutropenia is usually caused by treatment. When looking at your risk of getting an infection, doctors look at the number of granulocytes you have. Neutrophils are one type of granulocyte. Depending on the type of cancer you have and treatment you're getting, another thing doctors might look at in your blood counts is if the cells are mature or not. When a cell is mature, it works well and does its job. When a cell is immature, or less mature, it has not developed all the way and does not work like it should.
If your neutrophil count is low, the doctor may say you are neutropenic. For most people with cancer, having a low neutrophil count is the biggest risk factor for getting a serious infection. Ask your doctor if your cancer treatment will cause your neutrophil count to drop.
Some treatments, most often those given during a bone marrow (stem cell) transplant, can cause a shortage of lymphocytes. B and T lymphocytes help fight viruses, but have different jobs:
A high number of monocytes on a blood test might mean you have an infection.
You might hear your doctor or nurse talk about your absolute neutrophil count or ANC. This is the number of neutrophils you have in a certain amount of blood. Your health care team will use your ANC to get an idea of how well your immune system might work during treatment. A blood test called a complete blood count (CBC) is used to see how well your immune system is working. It measures your white blood cells (WBCs), and your cancer care team is able to figure out your ANC from your WBC count. Your cancer care team will use your ANC to get an idea of how your immune system is affected by treatment and how well it is working to protect you from infection.
As the ANC gets lower, the usual signs of infection, such as fever, pus, pain, swelling, and redness, may not show up when an infection starts. This is because these signs are caused by neutrophils fighting off germs, and if you don’t have enough neutrophils to fight infection, you won't produce the signs. This can make it hard to know if you have an infection. The good thing is that another WBC, called the monocyte, can still cause signs of infection in a person who has neutropenia. Sometimes in people with severe neutropenia a fever may be the only sign of an infection. The lower your ANC is and the longer it stays low, the higher your risk of infection will be.
Ask your doctor if your cancer treatment might cause your neutrophil count to drop. Your cancer care team will help you find the ANC on your lab results and can help explain more about it.
Treatment may include one or a combination of the following:
Talk to your cancer care team about what to watch for. Call your doctor if you have a fever (your cancer care team will let you know what temperature they consider a fever) or any other symptoms of neutropenia.
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.
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Last Revised: October 23, 2023
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