A white blood cell count below the normal range may be a symptom of cancer, a viral infection, an autoimmune disease or another cause, states Mayo Clinic. Identifying the exact cause is done through other tests. As the efficacy of their immune systems is reduced, patients with low white blood cell counts are advised to take every measure to avoid possible exposure to disease.
Congenital diseases, very strong infections and side effects of certain drugs can also cause a low white blood cell count, notes Mayo Clinic. Each of these conditions either destroys white blood cells faster than they can be replenished or impairs bone marrow function, reducing its capacity to produce new white blood cells or release them into the bloodstream to fight infection. Specific examples include leukemia, HIV/AIDS, hypersplenism, lupus and vitamin deficiency.
The lower bound for a normal white blood cell count is 4,000 white blood cells, or leukocytes, in one microliter of blood, Mayo Clinic explains. The cutoff is not strictly defined and differs between medical practices. Some adults may appear to be perfectly healthy despite having fewer than 4,000 leukocytes per microliter of blood. In children, the cutoff depends on the child’s sex and age.