A low white blood cell count, called leukopenia, may indicate bone marrow problems, autoimmune disorders, diseases involving the liver or spleen, certain cancers, or certain illnesses caused by viruses, states MedlinePlus. Severe bacterial infections, certain medications and radiation treatment for cancer may also lower white blood cell count.
Many medications decrease the number of white blood cells, including antibiotics, anticonvulsants, chemotherapy drugs, anti-thyroid pills and diuretics, notes MedlinePlus. Captopril, clozapine, sulfonamides, quinidine and ticlopidine may also cause a low white blood cell count. Because they are typically more susceptible to infection, some patients with a persistent low white blood cell count must take special precautions to prevent getting sick, explains Mayo Clinic. These precautions include washing hands regularly, avoiding people with colds or other illness, and wearing a face mask.
Doctors order a white blood cell count, along with other tests, to help diagnose illnesses, according to Mayo Clinic. No preparation is usually necessary before a white blood cell count, which is obtained by taking a blood sample from a vein, states MedlinePlus. A normal white blood cell count ranges from 4,500 to 10,000 white blood cells per microliter. Because normal value ranges sometimes differ among laboratories, it's best for patients to discuss individual results with their doctor.