What Are Reasons for Low White Blood Count?

White blood cells play an important role in the immune system as they scavenge the blood for invading bacteria, viruses and other foreign material. Low white blood cell counts, a condition called neutropenia, is usually mild and asymptomatic. Severe, chronic neutropenia, however, can be serious as it can result in lethal infections.

Cancer Chemotherapy

Cancer chemotherapy is a leading cause of neutropenia. White blood cells are produced by the bone marrow. Tirgan Oncology Associates and the National Neutropenia Network explain that chemotherapeutic drugs are toxic to the bone marrow and slow down white cell production. For this reason, oncologists often prescribe drugs that increase white cell levels in individuals undergoing chemotherapy. Drugs such as Neulasta will raise white cell levels in such patients and have been shown to be effective in preventing infection in cancer patients.


The National Neutropenia Network explains that exposure to radiation is also a cause of neutropenia. While environmental exposure to marrow-damaging levels of radiation are rare, radiation treatments for certain cancers can damage the bone marrow and lower white cell counts.


Leukemia is a devastating cancer of the white cell-producing cells in the bone marrow. The Mayo Clinic describes how leukemia causes the bone marrow to produce large amounts of abnormal, non-functional white cells. As these non-functional white cells flood the circulation, normal, disease-fighting white cells are lost and the body becomes more susceptible to infection.


According to the Merck Manual, rapid, overwhelming infections can also be a cause of neutropenia. If bacteria or viruses reproduce rapidly in the body during an infection, they can outpace white blood cell production while eating up white blood cells to cause neutropenia. If a patient with neutropenia is found to have a fever, a common sign of infection, he will be administered antibiotic and antifungal drugs to fight off infection.

Enlarged Spleen

The spleen is a small, fist-sized organ located in the abdomen that plays an important role in blood homeostasis and the immune system. According to the Merck Manual, certain disorders of the liver, blood or immune system can cause the spleen to trap blood cells and enlarge itself. As the spleen collects white blood cells from the circulation, an individual may experience neutropenia and become susceptible to infection.

About this Author

Chad Stone is a cancer researcher based in the Pacific Northwest. Dr. Stone has been an active writer since 2003 and has published high-profile articles on the molecular mechanisms of cancer and other diseases. Dr. Stone is a specialist in cancer metastasis of breast, colon, kidney and other carcinomas.