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By Mayo Clinic staffA low white blood cell count, or leukopenia, is a decrease in disease-fighting cells (leukocytes) circulating in your blood.
The benchmark for a low white blood cell count may vary slightly among medical practices. A low white blood cell count in adults is generally defined as fewer than 3,500 white blood cells per microliter of blood. A low white blood cell count in children varies with age and sex.
There are several subtypes of white blood cells, each with a different disease-fighting activity. If you have a low white blood cell count, you most likely have a decrease in only one type. A related laboratory test determines the percentage of each type of white blood cell in a sample.