A low white blood cell (WBC) count, known as leukopenia, can be caused by diseases such as leukemia, cancer, lupus, rheumatoid arthritis and some medications, according to the Mayo Clinic. Normal white blood count is 5,000 to 10,000 WBCs per microliter.There are two types of white blood cells: neutrophils and lymphocytes. Either or both may be decreased in leukopenia. If neutrophils are low, the condition is called neutropenia; if lymphocytes are low, the condition is called lymphcytopenia. Both can cause symptoms.
Neutrophils are the body's main line of defense against infection, according to the Merck Manual, so if neutrophils drop below 500 per microliter, the chance of developing a bacterial or fungal infection increases. A decrease in lymphocytes can also increase the risk of infection. Even a mild infection can be serious if you have leukocytosis, because your body can't fight off the infection. Leukocytosis not only makes it more likely that you'll develop an infection, it also makes it more likely an infection will escalate and become more serious, according to the Mayo Clinic.
Fever over 100.5 degrees F is a symptom of neutropenia, according to Cancer Treatment Centers of America (CTCA). Fever is usually related to infection.
Sores in the mucous membranes of the mouth and gums and around the anus are common symptoms of neutropenia, according to the Merck Manual. Small cuts or injuries may become easily infected, with redness, swelling or pain around the wound. Other symptoms of neutropenia-related infection are caused by the body system that's infected; an infection in the lungs causes shortness of breath, while an infection of the urinary tract may cause burning and pain upon urination.