Neutropenia

Abstract Neutropenia is a decrease in the number of neutrophilic leucocytes in the blood. Neutropenia is defined as an absolute neutrophil count or ANC (total white blood cells per litre multiplied by the percentage of neutrophils) more than two standard deviations below the normal mean. The ANC is usually more than 2.0 × 10 9 L −1 . Neutropenia is graded as mild, moderate or severe; severe is less than 0.5 × 10 9 L −1 . Severe neutropenia predisposes to a high risk of bacterial and fungal infections. Neutropenia occurs both as an acquired and as an inherited disorder. Drugs and autoimmune diseases are the common causes of acquired neutropenia. There are many hereditary causes of neutropenia; all of these are rare conditions, but some are quite severe. Proper treatment depends on understanding the cause of neutropenia and its expected duration. Short periods of neutropenia can be managed with careful observation or antibiotics. Patients with severe chronic neutropenia benefit from long‐term treatment with granulocyte colony‐stimulating factor (G‐CSF). Key Concepts Neutrophils are critical for normal defence from infections by bacteria on body surfaces. Blood neutrophil levels below normal, that is, neutropenia, predispose to bacterial and fungal infections. The bone marrow produces neutrophils from haematopoietic stem cells through an orderly process that takes about 10–14 days. Neutropenia is usually due to acquired or intrinsic/hereditary disorders affecting bone marrow production of these cells. When neutrophil production is interrupted by drugs or diseases recovery often takes several days. The risk of infection in patients with neutropenia depends on the severity of neutropenia and its duration. With a brief period, that is, 1–3 days, the risk is relatively low. Severe neutropenia lasting longer is associated with a steadily increasing risk of severe infection and even death. Proper management of neutropenia requires understanding its cause and the expected duration of neutropenia. When it is due to drugs, either cancer chemotherapy or as an idiosyncratic reaction to other drugs, the duration is usually relatively brief and can be managed with observation or antibiotics. Neutropenia lasting more than about 5–7 days and more chronic neutropenia predispose patients to a much higher risk of bacterial and fungal infections. These patients benefit from treatment with granulocyte colony‐stimulating factor (G‐CSF). It is now possible to identify the genetic cause for severe chronic neutropenia in many patients through deoxyribonucleic acid (DNA) sequencing studies. Understanding of the molecular and cellular basis for these disorders is growing rapidly.