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Understanding Low White Blood Cell Counts

How a low white blood cell count affects health and how the doctor might treat it

By , Caring.com senior editor
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White blood cells are the body's best defensive weapons in the fight against germs and disease, so when white blood cell counts drop as a result of chemotherapy, radiation treatment, or certain types of cancer, it puts the patient in a vulnerable position. Without adequate protection from these disease-fighting cells, viruses and bacteria suddenly become much more serious threats.

Why does chemotherapy make white blood cell counts drop?

Think of chemotherapy as a smart bomb: It only targets certain types of cells, particularly those that grow and divide rapidly. That means it targets tumor cells, but it also means that white blood cells, which are produced in the bone marrow and have a rapid turnover rate, can be damaged as well. White blood cell counts, sometimes called leukocyte counts, drop with most chemo drugs. Neutrophils, which are a specific type of white blood cell, are the most potent disease fighters. The doctor may refer to a low white blood cell count as neutropenia, since a shortage of neutrophils is often what the doctor is most concerned about.

What are the risks of having a low white blood cell count?

White blood cells, or leukocytes, help fight bacteria and viruses. They're like the armed guards at the gates of the body, driving back the invaders. When there are too few white blood cells, a patient's immune system is compromised, putting him or her at increased risk of all types of infection : bacterial, viral, and fungal.

Low White Blood Cell Count Symptoms, Tests & Prevention

Why is there more than one test for white blood cell counts?

A standard blood count calculates the number of white blood cells (WBCs) per microliter of blood. This is also called the total leukocyte count, or TLC. A healthy person has between 4,500 and 11,000 of them. A second test, called a differential count, or "diff," breaks down the count into five different types of white blood cells: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Healthy blood is made up of approximately 60 percent neutrophils, 30 percent lymphocytes, 5 percent monocytes, 4 percent eosinophils, and 1 percent basophils. Knowing which types of white blood cells have been most affected helps the doctor evaluate a patient's risk of becoming immune suppressed.

One way doctors measure this risk is with a test called the absolute neutrophil count, or ANC, which calculates the percent of neutrophils in the total white blood count. The risk of infection increases as the ANC falls; if someone's ANC falls below 1,000, he has a moderate risk of infection, while an ANC under 500 carries a high risk of infection.

Is there a way to prevent white blood cell count from dropping?

Yes, if the doctor determines you or the person you're caring for is at risk of losing too many white blood cells, she can prescribe a white blood cell booster, more formally known as a colony stimulating factor, or CSF. These popular drugs are called filgrastim and pegfilgrastim -- or Neupogen and Neulasta, their brand names. It's common to begin taking the drugs at the start of chemotherapy, in the hope that they'll boost white cell production and strengthen the body's natural defense system. The doctor can also prescribe them later to try to bring the white count up if it doesn't rise fast enough on its own.

What symptoms should I watch for related to low white blood cell count?

When white count is low, you need to be on the alert for fever, which is usually the first sign that the body is fighting off an infection. Someone with low white cell blood count has less resistance to colds and flu, so those are definite threats, but other kinds of infections can appear as well. Gastrointestinal infections may show up as cramping or diarrhea, while a bladder or urinary tract infection makes it hurt to urinate. Even a tiny cut or scratch can become infected, so watch for redness, swelling, pus, or tenderness around any wound. Also keep an eye out for sinus infections, usually evidenced by a stuffy nose or headache; rectal bleeding; or signs of lung infection such as coughing up fluid.

Low White Blood Cell Count Treatment & Prognosis

How long will it take for low white blood cell count to come back up?

It's common for white blood cell count to begin to drop a few days after each chemo treatment and will be at its lowest level during weeks two and three following chemo. Then, as the bone marrow gradually begins to recover and produce new white blood cells, the count will rise. If this doesn't happen, or if you see signs of infection, the doctor may prescribe another CSF to try to boost white blood cell production.

If someone's white blood cell count is low, but he or she is otherwise healthy, is there reason to worry?

That's the mystery of it: Almost every cancer patient experiences a drop in white count following chemotherapy (also after some types of radiation), but only a small percentage of patients experience serious infection. Whether someone is going to get sick depends on a host of factors, such as age, another condition that might affect the immune system, other medications, and his or her general state of health before the chemo. The doctor will likely say not to worry about a low white blood cell count unless the absolute neutrophil count, or ANC, drops into the high-risk category. And even then, the usual strategy is to simply become more vigilant in watching for signs of infection.