Neutrophils are a specific kind of white blood cell that help prevent and fight infections. The presence of abnormally low levels of neutrophils in the circulating blood is referred to as neutropenia, the most serious complication of chemotherapy. It is almost always due to impairment of bone marrow to produce cells and typically occurs 3-7 days following administration of the chemotherapy drugs. The condition of low level of neutrophils continues for several days before recovering to normal levels.  It is especially severe in patients who receive aggressive treatments. The patients may have fever and infection or may have no symptom at all even in most sever cases. Patients with mild neutropenia can develop serious problems.

Even in the most severe cases, it may have no signs at all, or it may cause and infection. Complete evaluation must be taken when patients receiving chemotherapy develop fever. Drugs for lowering fever like Tylenol or Aspirin should be avoided since they mask the symptom of infection, unless prescribed by the medical oncologist after a proper evaluation.