Leukopenia is the medical term for a low white blood cell count. The white blood cells are part of the immune system. They protect the body from infection and act as the primary responders when infection occurs. A low white cell count increases vulnerability to serious infections. Genetic disorders, systemic and bone marrow infections, and medications can cause a low white cell count.
Fanconi Anemia
Fanconi anemia is an uncommon, inherited disorder of the bone marrow. A gene abnormality causes decreased production of red blood cells, white blood cells and platelets. The National Heart, Lung and Blood Institute notes common symptoms of Fanconi anemia include fatigue, frequent infections, and easy bruising and bleeding. People with this disorder also frequently have birth defects affecting the heart, bones, kidneys and skin.
Aplastic Anemia
Aplastic anemia describes bone marrow failure that is not due to a genetic condition. Often presenting in adolescents and young adults, this disorder causes markedly decreased bone marrow production of red and white blood cells, and platelets. Aplastic anemia causes fatigue and shortness of breath due to severe anemia, frequent infections due to abnormally low white blood cell levels, and easy bleeding caused by insufficient platelets. The Merck Manual for Healthcare Professionals explains that toxins and medications may precipitate aplastic anemia. In approximately 50 percent of cases, the cause is unknown.
Systemic Viral and Bone Marrow Infections
Some systemic viral and tick-borne infections can cause decreased white blood cell production and an associated low white blood cell count. In a 2009 research article published in Pediatric Blood and Cancer, Dr. J.M. Sheen and colleagues reported low white blood cell counts associated with influenza, cytomegalovirus and Epstein-Barr virus infections. Direct infection of the bone marrow can also cause decreased production of white blood cells. The University of California, San Francisco reports that fungal and tuberculosis infections of the bone marrow may cause leukopenia in people with HIV.
Overwhelming Bacterial Infections
Serious bacterial infections such as meningitis, bloodstream infections and widespread skin infections may cause a low white blood cell count due to increased utilization. The white blood cells migrate to the site of infection in large numbers to combat the invading bacteria. The Cleveland Clinic notes that bone marrow production may not be able to keep up with the increased demand for white blood cells caused by overwhelming bacterial infection.
Chemotherapy
The American Cancer Society advises that many cancer chemotherapy drugs cause decreased bone marrow production of white blood cells, red blood cells and platelets. A marked decrease in circulating white blood cells increases vulnerability to serious infections. To counteract chemotherapy-induced bone marrow suppression of white blood cell production, people undergoing chemotherapy are often treated with medications called growth factors to boost blood cell production.
