White blood cells (WBCs) fight infections from bacteria, viruses, fungi, and other germs. One important type of WBC is the neutrophil. These cells are made in the bone marrow and travel in the blood throughout the body. They sense infections, gather at sites of infection, and destroy the germs.

When the body has too few neutrophils, the condition is called neutropenia. This makes it harder for the body to fight off infection, and a person is more likely to get sick. In general, an adult who has fewer than 1,000 neutrophils in a microliter of blood has neutropenia.

If the neutrophil count is very low, fewer than 500 neutrophils in a microliter of blood, it is called severe neutropenia. When the neutrophil count gets this low, even the bacteria normally living in a person's mouth, skin, and gut can cause serious infections.

Neutropenia and cancer; Absolute neutrophil count and cancer; ANC and cancer

A person with cancer can develop a low WBC count from the cancer or from treatment for the cancer. Cancer may be in the bone marrow, causing fewer neutrophils to be made. The WBC count can also go down when cancer is treated with chemotherapy drugs, which slow bone marrow production of healthy WBCs.

When your blood is tested, ask for your WBC count and specifically, your neutrophil count. If your counts are low, do what you can to prevent infections. Know the signs of infection and what to do if you have them.

Prevent infections by taking the following measures:

• Be careful with pets and other animals to avoid catching infections from them.
• Practice safe eating and drinking habits.
• Wash your hands often with soap and water.
• Stay away from people who have symptoms of an infection.
• Avoid traveling and crowded public places.

If you have any of the following symptoms, contact your health care provider:

• Fevers, chills, or sweats.
• Diarrhea that does not go away or is bloody.
• Severe nausea and vomiting.
• Being unable to eat or drink.
• Extreme weakness.
• Redness, swelling, or drainage from any place where you have an IV line inserted into your body.
• A new skin rash or blisters.
• Pain in your stomach area.
• A very bad headache or one that does not go away.
• A cough that is getting worse.
• Trouble breathing when you are at rest or when you are doing simple tasks.
• Burning when you urinate.

American Cancer Society website. Why people with cancer are more likely to get infections. www.cancer.org/cancer/managing-cancer/side-effects/low-blood-counts/infections/why-people-with-cancer-are-at-risk.html. Updated March 13, 2020. Accessed May 8, 2023.

Centers for Disease Control and Prevention website. Preventing infections in cancer patients. www.cdc.gov/cancer/preventinfections/index.htm. Updated January 9, 2023. Accessed May 8, 2023.

Freifeld AG, Kaul DR. Infection in the patient with cancer. In: Niederhuber JE, Armitage JO, Kastan MB, Doroshow JH, Tepper JE, eds. Abeloff's Clinical Oncology. 6th ed. Philadelphia, PA: Elsevier; 2020:chap 34.