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.

• Leukemia
• Chemotherapy
• Radiation therapy

Drugs

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

Infections

• Chickenpox
• Epstein-Barr
• Hepatitis A
• Hepatitis B
• Hepatitis C
• HIV/AIDS
• Measles
• Salmonella infection
• Sepsis (an overwhelming bloodstream infection)

Autoimmune diseases

• Granulomatosis with polyangiitis (formerly called Wegener's granulomatosis)
• Lupus
• Rheumatoid arthritis

Bone marrow disorders

• Aplastic anemia
• Myelodysplastic syndromes
• Myelofibrosis

Additional causes

• Conditions present at birth, such as Kostmann's syndrome (a disorder involving low production of neutrophils)
• Unknown reasons, called chronic idiopathic neutropenia
• Vitamin deficiencies
• Abnormalities of the spleen

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

Neutropenia doesn't cause obvious symptoms, so it alone probably won't prompt you to go to your doctor. Neutropenia is usually discovered when blood tests are done for other reasons.

Talk to your doctor about what your test results mean. A finding of neutropenia combined with the results from other tests might indicate the cause of your condition. Your doctor also may need to repeat the blood test to confirm your results or order additional tests to find out what's causing your neutropenia.

If you've been diagnosed with neutropenia, call your doctor right away if you develop signs of an infection, which may include:

• Fever above 100.4 degrees F (38 degrees C)
• Chills and sweats
• A new or worsening cough
• Shortness of breath
• A mouth sore
• A sore throat
• Any changes in urination
• A stiff neck
• Diarrhea
• Vomiting
• Redness or swelling around any area where skin is broken or cut
• New vaginal discharge
• New pain

If you have neutropenia, your doctor may recommend measures to lessen your risk of infection, such as staying up to date on vaccinations, washing your hands regularly and thoroughly, wearing a face mask, and avoiding large crowds and anyone with a cold or other contagious illness.