Neutropenia (also called agranulocytosis or granulocytopenia) is an abnormally low number of neutrophils (a type of white blood cell) in the blood.
Neutrophils serve as the major defense of the body against acute bacterial and certain fungal infections. Neutrophils usually constitute about 45 to 75% of all white blood cells in the bloodstream. When the neutrophil count falls below 1,000 cells per microliter of blood, the risk of infection increases. When it falls below 500 cells per microliter, the risk of infection increases greatly. Without the key defense provided by neutrophils, people have problems controlling infections and are at risk of dying from an infection.
Neutropenia can develop if neutrophils are used up or destroyed in the bloodstream faster than the bone marrow can make new ones. With some bacterial infections, some allergic disorders, and some drug treatments, neutrophils are destroyed faster than they are produced. People with an autoimmune disease can make antibodies that destroy neutrophils and result in neutropenia. People with an enlarged spleen (see Spleen Disorders: Enlarged Spleen) may have a low neutrophil count because the enlarged spleen traps and destroys neutrophils.
Neutropenia can also develop if the production of neutrophils in the bone marrow is reduced, as can occur in some people with cancer, viral infections such as influenza, bacterial infections such as tuberculosis, myelofibrosis, or deficiencies of vitamin B12 or folate (folic acid). People who have received radiation therapy that involves the bone marrow may also develop neutropenia. Many drugs, including phenytoin, chloramphenicol, sulfa drugs, and many drugs used in cancer treatment (chemotherapy), as well as certain toxins (benzene and insecticides) can also impair the bone marrow's ability to produce neutrophils.
Production of neutrophils in the bone marrow is also affected by a disorder called aplastic anemia (in which the bone marrow may shut down production of all blood cells—see Anemia: Aplastic Anemia: When the Bone Marrow Shuts Down). Certain rare hereditary diseases also cause the number of neutrophils to decrease.
Symptoms and Diagnosis
Neutropenia can develop suddenly over a few hours or days in response to certain infections or exposures, or neutropenia can develop gradually. It may resolve quickly (when the infection resolves or the exposure stops), or it may last for months or years (chronic neutropenia). Because neutropenia itself has no specific symptoms, it is usually diagnosed when an infection occurs. People may develop fever and painful sores (ulcers) around the mouth and anus. Bacterial pneumonia and other severe infections can occur. In chronic neutropenia, the course may be less severe if the number of neutrophils is not extremely low, and the course can occasionally be intermittent (cyclic neutropenia).
When people have frequent or unusual infections, doctors suspect neutropenia and order a complete blood count to make the diagnosis. A low neutrophil count indicates neutropenia. In many cases, the neutropenia is expected and the cause is known, as in people receiving chemotherapy or radiation therapy. When the cause is not known, it must be determined. And whether the cause is known or not, doctors also must search for a hidden infection that may have been caused by the neutropenia.
Determination of cause:
Doctors ask about drug or toxic exposures and look for infections or other disorders that can cause the neutropenia. They frequently take a sample of bone marrow through a needle (see Symptoms and Diagnosis of Blood Disorders: Bone Marrow Examination). The bone marrow sample is examined under a microscope to determine whether it looks normal, has a normal number of neutrophil stem cells, and shows normal development of neutrophils. By determining whether the number of stem cells is decreased and whether these cells are maturing normally, doctors may be able to determine whether the problem lies in faulty production of the cells or whether too many cells are being used or destroyed in the bloodstream. Sometimes, the bone marrow examination indicates whether other diseases, such as leukemia or other cancers, or infections, such as tuberculosis, are affecting the bone marrow.
Evaluation for infection:
Because people with neutropenia might not have all the typical symptoms and examination findings of an infection, doctors ask people detailed questions about their symptoms and examine them from head to toe. Tests are done for any concerning findings, for example, if the person has abdominal discomfort, computed tomography (CT) of the abdomen may be done. Even if there are no specific findings, doctors typically also do urinalysis and urine culture, blood cultures, and a chest x-ray. When doctors do a culture, they take a sample of the material being tested (in this case, urine or blood) and send it to the laboratory to grow bacteria or other organisms that may be present.
The most important thing is to treat any infection that is found. In people with neutropenia, infections can rapidly become serious or fatal. Even if doctors cannot diagnose a specific infection, people who have fever are presumed to have an infection. Such people are given antibiotics effective against most usual causes.
The treatment of neutropenia itself depends on its cause and severity. Drugs that may cause neutropenia are stopped whenever possible, and exposures to suspected toxins are avoided. Sometimes the bone marrow recovers by itself without treatment. The neutropenia accompanying viral infections (such as influenza) may be transient and resolve after the infection has cleared. People who have mild neutropenia generally have no symptoms and may not need treatment.
People who have severe neutropenia can rapidly die as a result of infection because their bodies lack the means to fight invading organisms. When these people develop infections, they are generally hospitalized and immediately given strong antibiotics, even before the cause and exact location of the infection are identified. Fever, the symptom that usually indicates infection in people who have neutropenia, is an important sign that immediate medical attention is needed.
Growth factors called colony-stimulating factors, which stimulate the production of white blood cells, are sometimes helpful. Corticosteroids may help if the neutropenia is caused by an autoimmune reaction. Antithymocyte globulin or other types of therapy that suppress the activity of the immune system may be used when a disorder such as aplastic anemia is present.
When neutropenia is caused by another disorder (such as tuberculosis or leukemia or other cancers), treatment of the underlying disorder may resolve the neutropenia. For example, when neutropenia is caused by an enlarged spleen, removing the enlarged spleen may cure the neutropenia. Bone marrow (or stem cell) transplantation is not used to treat neutropenia per se, but it may be recommended to treat certain serious causes of neutropenia, such as aplastic anemia or leukemia.
Last full review/revision January 2013 by Mary Territo, MD