Neutropenia (noo-troe-PEE-nee-uh) occurs when you have too few neutrophils, a type of white blood cells. While all white blood cells help your body fight infections, neutrophils are important for fighting certain infections, especially those caused by bacteria.

You probably won’t know that you have neutropenia. People often only find out when they’ve had blood tests done for other reasons.

A single blood test showing low levels of neutrophils doesn’t necessarily mean you have neutropenia. These levels can vary from day to day, so if a blood test shows you have neutropenia, it needs to be repeated for confirmation.

Neutropenia can make you more vulnerable to infections. When neutropenia is severe, even the normal bacteria from your mouth and digestive tract can cause serious illness.

Numerous factors may cause neutropenia through destruction, decreased production or abnormal storage of neutrophils.

Cancer and cancer treatments

Cancer chemotherapy is a common cause of neutropenia. In addition to killing cancer cells, chemotherapy can also destroy neutrophils and other healthy cells.

1. Leukemia
2. Chemotherapy
3. Radiation therapy

Drugs

1. Medications used to treat overactive thyroid, such as methimazole (Tapazole) and propylthiouracil
2. Certain antibiotics, including vancomycin (Vancocin), penicillin G and oxacillin
3. Antiviral drugs, such as ganciclovir (Cytovene) and valganciclovir (Valcyte)
4. Anti-inflammatory medication for conditions such as ulcerative colitis or rheumatoid arthritis, including sulfasalazine (Azulfidine)
5. Some antipsychotic medications, such as clozapine (Clozaril, Fazaclo, others) and chlorpromazine
6. Drugs used to treat irregular heart rhythms, including quinidine and procainamide
7. Levamisole — a veterinary drug that’s not approved for human use in the United States, but may be mixed in with cocaine

Infections

1. Chickenpox
2. Epstein-Barr
3. Hepatitis A
4. Hepatitis B
5. Hepatitis C
6. HIV/AIDS
7. Measles
8. Salmonella infection
9. Sepsis (an overwhelming bloodstream infection)

Autoimmune diseases

1. Granulomatosis with polyangiitis (formerly called Wegener’s granulomatosis)
2. Lupus
3. Rheumatoid arthritis

Bone marrow disorders

1. Aplastic anemia
2. Myelodysplastic syndromes
3. Myelofibrosis

Additional causes

1. Conditions present at birth, such as Kostmann’s syndrome (a disorder involving low production of neutrophils)
2. Unknown reasons, called chronic idiopathic neutropenia
3. Vitamin deficiencies
4. Abnormalities of the spleen

People can have neutropenia without an increased risk of infection. This is known as benign neutropenia.

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