I have been told to take a bone marrow test because I have a low white blood cell count 2600 with 33% neutrophils and 9% atypical lymphocytes; hematocrit 38.5.

Do you know what this all means? What could be the worst case scenario?

White cells are the the cells that help fight off infection. A white count of 2600 (also referred to as 2.6) is indeed low, though not very low. Typically the white count should be above 4000 (also referred to as 4.0). Sometimes a bone marrow examination is performed to help figure out what's going on. It's difficult to comment as to whether or not you should have a biopsy without knowing much more about your situation.

Are you HIV positive? If so, do you have symptoms (fever, chills, night sweats, weight loss). If so, then a low white count could be a sign that something else is going on.

Are you an any medication which could lower your white count? If you are taking AZT, then a low white count is to be expected.

Are you an African-American? African-Americans typically have lower white counts than Caucasians. The lower white counts in African-Americans usually cause no problems and represent nothing more than an interesting laboratory finding.

Have you recently been ill. It is not unusual that after a viral infection (e.g. the flu) that the bone marrow temporarily slows down. As a consequence, you can get a low white count on that basis.

It's also important to know how long you've had a low white count. It is not unusual for low white counts to be transient in nature, lasting typically a few weeks. Have you seen a hematologist? (S)he should be able to help you assess the situation.