White blood cells play an important role in the immune system as they scavenge the blood for invading bacteria and viruses. Individuals may become susceptible to infection when white blood cell levels become low, a condition known as neutropenia. Mild neutropenia is typically asymptomatic, but severe, chronic neutropenia can be serious and result in a fatal infection.
Leukemia
Leukemia is a cancer of the blood producing cells of the bone marrow. The Mayo Clinic explains that these cells produce large numbers of non-functional white cells when they become diseased. Although an individual with leukemia may have a large number of white blood cells in their blood, the numbers of functional disease fighting cells may be low.
Chemotherapy and Radiation Treatment
Neutropenia is often associated with cancer treatment, as chemotherapeutic drugs can damage white blood cell-producing cells in the bone marrow. The National Neutropenia Network explains that radiation treatment can similarly destroy bone marrow and lead to neutropenia. Oncologists treat cancer with a course of agents that help to bring up white cell numbers in patients undergoing chemotherapy or radiation treatments. These agents include granulocyte colony stimulating factor, corticosteroids or drugs such as Neulasta. Cancer patients, in rare cases, may need a bone marrow transplant to replace destroyed white cell-producing cells.
Infection
The Merck Manual explains that infection is a common cause of mild, acute neutropenia. A virus or bacteria multiplies in the body and may grow more rapidly than the body can produce white cells, leading to a net loss in white cells. Common infections associated with neutropenia include tuberculosis and influenza.
Enlarged Spleen
The spleen is a fist-sized organ located in the abdomen that plays an important function in the immune system. Certain disorders of the blood or immune system may cause the spleen to become enlarged. According to the Merck Manual, the spleen can act as a trap for white blood cells that collect in the spleen when it becomes enlarged. In rare cases, a splenectomy, or removal of the spleen, may be necessary to raise white cell numbers.
