What is a low white blood cell count? A low white blood cell (WBC) count is a decreased number of white blood cells (leukocytes) in the blood. A low WBC count is referred to medically as leukopenia. WBCs, which are produced in the bone marrow, are an important part of your immune system and your body’s natural weapon to fight off bacteria, viruses and other germs. When you have a low white blood cell count you may be immunosuppressed, which means that you are more vulnerable to potentially serious infections that do not go away or are hard to treat. A low WBC count is usually discovered by your physician or health care provider during routine testing or through the course of diagnosis and treatment for an underlying disease, disorder or condition. A normal WBC count is approximately 4,500 to 10,000 WBCs per microliter of blood. A low WBC count is generally below 3,500 WBCs per microliter of blood, but this number varies depending on the medical laboratory, the particular test used, and the individual medical practice. The significance of a low WBC count varies and may be more (or less) serious depending on your medical history, overall health, and the underlying disease, disorder or condition. Some people may naturally have a mildly low WBC count. The normal range of low to high WBC counts also varies by age and gender. A low WBC count is often linked to problems with the bone marrow and the inability to make enough white blood cells. Autoimmune diseases that attack your white blood cells can also lead to a low WBC count. Several different prescribed drugs, including chemotherapy, are known to decrease WBC production or destroy WBCs. A low WBC count can be serious because it increases your risk of developing a potentially life-threatening infection. If you have a low WBC count, you will probably be advised by your medical professional to avoid situations that expose you to infectious and contagious diseases. Seek prompt medical care if you have a low WBC count and have signs of an infection, such as a fever, swollen lymph nodes, sore throat, or skin lesions.