Why Is My White Blood Cell Count Low?

White blood cells, also called leukocytes, fight infection. They move throughout your body in your blood, looking for invaders. And your body is continuously making a fresh supply.

Your doctor measures how many of these cells you have by sending some of your blood to a lab to do a complete blood count, or CBC. Your white blood cell count is one of the numbers you get back from this test. It may point toward or confirm a diagnosis, or show whether a treatment is working or not.

Most often, a low white blood cell count is nothing to worry about.

What Is "Low"?

How many white blood cells (WBCs) someone has varies, but the normal range is usually between 4,000 and 11,000 per microliter of blood.

A blood test that shows a WBC count of less than 4,000 per microliter (some labs say less than 4,500) could mean your body may not be able to fight infection the way it should. A low number is sometimes called leukopenia.

Causes

Your doctor will do a physical exam and consider symptoms that you have along with your past medical issues to figure out what's behind your result.

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Bone marrow problems: The spongy center of your bones, which is called the bone marrow, makes blood cells. Low WBC counts are often linked to bone marrow problems. Being around certain chemicals, like benzene and pesticides, as well as some types of cancer and cancer treatments including chemotherapy and radiation, can hurt your bone marrow's ability to make WBCs.

Autoimmune disorders: Some autoimmune diseases, like lupus and rheumatoid arthritis, will tell your body to attack and destroy its own WBCs.

Infection: Viruses can affect your bone marrow and cause low WBCs for a while. Severe infections, like blood infections, can lead to your body using up WBCs faster than it can make them. HIV kills a specific kind of white blood cell.

Medicines: Some drugs, including antibiotics, can destroy WBCs.

Nutrition: Not eating well or low levels of certain vitamins, such as folic acidand B12, can affect how your body makes WBCs. Alcohol abuse can mess with the nutrients in your body and with WBC counts, too.

Spleen problems: The spleen also makes WBCs. Infections, blood clots, and other problems can make it swell and not work the way it should. This will drop your WBC count.