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Q. I have low white cells and the doctor wants to do a bone marrow test to see what's abnormal. I'm concerned. What causes a low white cell count for a long time?

- S.N., Lake Wales, Fla.

A. White blood cells (leukocytes or WBCs) function as part of the body's defense against infection and other foreign substances. Like other blood cells, WBCs are produced in bone marrow from precursor or stem cells.

To do their job, an adequate number of white cells must be produced in the bone marrow and made available in the bloodstream to get to where they're needed. When either production or availability is reduced, or when the white cells are being destroyed too rapidly, the cell count goes down. Too few white cells (as well as too many) indicate a problem.

White cell counts usually go up with an infection, but the count may actually be lowered during part of the illness as the white cells are destroyed faster than they can be replaced. And even if there are enough white cells, if they do not function normally, such as in leukemia, signs and symptoms of disease will appear.

The normal circulating white blood count varies from person to person and with age. Adult white cell counts range from 4,000 to 10,000 per microliter of blood. Remember to keep records of all of your test results to be able to follow what's "normal" for you.

There are five major types of white cells: neutrophils, lymphocytes, monocytes, eosinophils and basophils.

Neutrophils are a type of white blood cell primarily directed to fight viral and bacterial infections. Because neutrophils account for approximately 70 percent of total white blood cells, low white counts usually means low numbers of neutrophils.

When the number of neutrophils gets below about 1,500 per microliter, the condition is called neutropenia. Neutropenia can develop suddenly (acute) or can last for months and even years (chronic).

A decreased number of neutrophils can be due to low production in the bone marrow or destruction of large numbers of the cells while fighting infection.

Certain drugs, such as chemotherapy drugs, and certain diseases, including some inherited diseases, can also cause neutropenia.

Lymphocytopenia is the abnormally low count of lymphocytes. Lymphocytes comprise 15 to 40 percent of all white cells.

Lymphocytes protect the body against viral infections and help control bacterial and fungal infection. They also produce antibodies for the immune system and help fight cancer.

Leukemias are cancers of the blood cells. The cause of most leukemias is unknown, but exposure to radiation, chemicals such as benzene, and some drugs are associated with development of the condition.

With leukemia, the number of circulating white cells can be decreased, normal or increased, but the number of red cells and platelets are nearly always decreased as well. The decrease in red cells and platelets is often the first step in diagnosing leukemia.

Diagnosis to identify the cause of low white cell counts begins with reviewing symptoms, such as frequent or unusual infections, if seen, and a blood test. After blood is taken and the white cells are counted, the next step is to examine the white blood cells under a microscope to see if they look cancerous or immature.

Often a bone marrow biopsy is recommended to confirm the diagnosis and to assess the severity of the disease if one is present. A sample of bone marrow aspirated from the biopsy is examined under a microscope to determine if normal white cells are being produced. This is not a pleasant test and you should discuss the benefits and risks with your doctor before having it done.

It sounds like you may have a chronic neutropenia and your doctor wants to find out why. When next you meet with the doctor, be sure to find out what is suspected and why, then learn what you can about your condition.

Write to Allen Douma in care of kALIVE, 1777 N.E. Loop 410, San Antonio, Texas 78217, or contact him at This column is not intended to take the place of consultation with a health-care provider.

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