DEAR MAYO CLINIC: I was told after my recent physical that my white blood cell count was low. Is this something to be concerned about? Am I more susceptible to colds or viruses?

ANSWER: A low white blood cell count can sometimes be a sign of an underlying medical problem, but not always. First, it's important to determine what your health care provider means by "low." Not all medical laboratories use the same range to decide what's normal and what's not. Second, you need to consider factors such as your age, gender and ethnic group. Some groups of people just have naturally lower white blood cell levels than others. If your white blood cell count is truly lower than it should be, then further investigation is warranted to uncover the root cause.

As part of your immune system, white blood cells fight disease and are important for the body's defense against infections. A chronically low white blood cell count (leukopenia) can make you vulnerable to bacterial infections and could signal a serious health problem. Before you start investigating the cause of a low white blood cell count, though, it's important to discuss with your doctor what your test results mean.

Different laboratories classify low white blood cell counts differently. Generally, a count lower than 3,500 white blood cells per microliter of blood is considered a low white blood cell count. But ask your doctor what the normal range is for the laboratory he or she uses. It may also be helpful to discuss exactly how far outside that range your number falls. A white blood cell count that's just slightly below the cutoff for the established normal range may actually still be normal and not require further evaluation.

In addition, what would be considered a low white blood cell count for some people may be a normal finding for others. For example, African-Americans tend to have lower white blood cell counts than Caucasians. It's also not uncommon for young Caucasian women to have white blood cell counts that fall slightly below the normal reference ranges. Talk to your doctor about how individual factors may affect your white blood cell levels.

With all that in mind, if you and your doctor determine that your white blood cell count is lower than it should be, that is cause for concern. Because a low white blood cell count cannot, in and of itself, be used to diagnose a specific disease or disorder, you'll likely need more testing to further assess your condition. Underlying causes for a low white blood cell count can range from benign disorders, such as vitamin deficiencies, to more serious blood diseases, such as leukemia or lymphoma.

A truly low white blood cell count also puts you at higher risk for infections -- typically bacterial infections. But viral infections also may be a concern. To help reduce your infection risk, your doctor may suggest you wear a facemask and avoid anyone with a cold or other illness. Washing your hands regularly and thoroughly can also help reduce risk. Ask your doctor if there are other precautions you should take to help avoid infections. -- Rajiv Pruthi, M.B.B.S., Hematology, Mayo Clinic, Rochester, Minn.

Medical Edge from Mayo Clinic is an educational resource and doesn't replace regular medical care.

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