We designate severe neutropenia as an absolute neutrophil count of less than 0.5 x 109/L. This state is an emergency situation, due to the risk of life-threatening infections. Drugs and viral infections are common causes of neutropenia.
Patients usually a have high fever and ulcerous lesions of the mucous membranes of the mouth, throat and anus. A viral infection may precede. Medications associated with severe neutropenia include: propylthiouracil, aminopyrine, non-steroidal anti-inflammatory drugs (e.g. phenylbutazone that is rarely used), antibiotics (e.g. chloramphenicol) and others. Drug-induced neutropenia usually resolves with cessation of the offending drug.
The infrequent neutrophils are usually toxic-appearing. Only lymphocytes and monocytes are present in the peripheral blood.
Granulopoiesis can be decreased or increased. However, myeloblasts and promyelocytes may be increased because of maturation arrest, i.e. myelopoiesis does not proceed beyond the promyelocyte stage, or the bone marrow is recovering.