White blood cells, produced in the bone marrow, are a part of the immune system responsible for fighting off abnormal cells and invading organisms. The five types of white blood cells, neutrophils--the most common--monocytes, lymphocytes, eosinophils and basophils fight infection presented in daily life. According to the Mayo Clinic, a low white blood cell count, or leukopenia, is defined as fewer than 3,500 white blood cells per microliter in adults. Children have varying definition parameters depending on their age and race. A decrease in the amount of white blood cells increases the risk of complications from common bacteria and viruses.
Medications
According to the Mayo Clinic some medications impact the number and function of white blood cells. Immunosupressive drugs, certain antibiotics, and some antidepressants can cause leukopenia over time. A few antipsychotic medications, such as clozapine, will reduce the number of white blood cells. Corticosteroids usually cause the white blood cell count to rise, but when given to a person with severe infection, this will be reversed or nonexistent, according to The Medical News.
Therapy
In those with cancer, chemotherapy and radiation therapy will possibly produce leukopenia. As cancer cells are killed with these therapies, other cells including white blood cells can die as well. Certain cancers in which bone marrow is affected will also cause a reduction in the production of white blood cells.
Infection
Some bacterial, viral or fungal infections overwhelm the immune system and white blood cells are destroyed faster than they are being produced, which would cause a low count. Some examples include influenza, lupus, Hodgkin's lymphoma, certain cancers in which malignant cells overwhelm white blood cell production in the bone marrow, sepsis, and tuberculosis, according to the Mayo Clinic. Also, some viral infections can disrupt bone marrow function, causing the production of white blood cells to reduce to a rate which may not be adequate, causing a low white blood cell count. One example of this includes HIV and AIDS.
Other Disorders
According to the Mayo Clinic, other conditions and disorders can cause leukopenia. Autoimmune disorders in which white blood cells or bone marrow cells are destroyed are a main cause. Bone marrow function can also be reduced in certain congenital or hereditary disorders such as Kostmann's syndrome. Myelokathexis is another congenital disorder in which white blood cells do not enter the bloodstream. Hypersplenism involves the destruction of white blood cells by the spleen. Anemia and certain allergies are other conditions that potentially cause leukopenia.
