Neutropenia itself is a rare entity, but can be clinically common in oncology and immunocompromised individuals as a result of chemotherapy (drug-induced neutropenia). Additionally, acute neutropenia can be commonly seen from people recovering from a viral infection or in a post-viral state. Meanwhile, several subtypes of neutropenia exist which are rarer and chronic, including acquired (idiopathic) neutropenia, cyclic neutropenia, autoimmune neutropenia, and congenital neutropenia. Neutropenia that is developed in response to chemotherapy typically becomes evident in seven to fourteen days after treatment. Conditions that indicate the presence of neutropenic fever are implanted devices; leukemia induction; the compromise of mucosal, mucociliary and cutaneous barriers; a rapid decline in absolute neutrophil count, duration of neutropenia >7–10 days, and other illnesses that exist in the patient. Signs of infection can be subtle. Fevers are a common and early observation. Sometimes overlooked is the presence of hypothermia, which can be present in sepsis. Physical examination and accessing the history and physical examination is focussed on sites of infection. Indwelling line sites, areas of skin breakdown, sinuses, nasopharynx, bronchi and lungs, alimentary tract, and skin are assessed. The diagnosis of neutropenia is done via the low neutrophil count detection on a complete blood count. Generally, other investigations are required to arrive at the right diagnosis. When the diagnosis is uncertain, or serious causes are suspected, bone marrow biopsy may be necessary. Other investigations commonly performed: serial neutrophil counts for suspected cyclic neutropenia, tests for antineutrophil antibodies, autoantibody screen (and investigations for systemic lupus erythematosus), vitamin B12 and folate assays. Rectal examinations are usually not performed due to the increased risk of introducing bacteria into the blood stream and the possible development of rectal abscesses. Generally accepted reference range for absolute neutrophil count (ANC) in adults is 1500 to 8000 cells per microliter (µl) of blood. Three general guidelines are used to classify the severity of neutropenia based on the ANC (expressed below in cells/µl):  Each of these are either derived from laboratory tests or via the formula below:  ANC = formula_1  Recombinant granulocyte-colony stimulating factor preparations, such as filgrastim can be effective in people with congenital forms of neutropenia including severe congenital neutropenia and cyclic neutropenia; the amount needed (dosage) to stabilize the neutrophil count varies considerably (depending on the individual's condition).