Fever associated with an abnormally low neutrophil level, usually caused by infection. This condition is treated with empirical antibiotic therapy pending the results of cultures. Neutropenia may be caused by many diseases and conditions, including chemotherapy, radiation exposure, aplastic anemia, bone marrow infiltration from malignancy, and complications of bone marrow transplantation. The risk of potentially life-threatening infection is substantial when the absolute neutrophil count is below 500/ mm3.