Infections in People With Cancer

Low white blood cell (neutrophil) counts and the risk of infection

Certain cancer treatments (such as chemotherapy, radiation therapy, surgery, stem cell or bone marrow transplant, or steroids) or the cancer itself can suppress or weaken the immune system. These treatments can lower the number of white blood cells (WBCs) and other immune system cells. Treatment can also cause these cells to not work as well as they should. This is called immunosuppression. It’s much easier to get an infection when there aren’t enough WBCs to destroy germs, especially the type of WBCs called neutrophils.

Neutrophils are a very important defense against most types of infection. When looking at your risk of getting an infection, doctors look at the number of neutrophils you have. A low neutrophil count is called neutropenia. The doctor may say you are neutropenic.

It’s possible for your total WBC count to be in the normal range while your neutrophil count is low. But because neutrophils normally make up the largest part of the total white blood cell count, the WBC count is usually low when the neutrophil count is low.

What is an absolute neutrophil count (ANC)?

You might hear your doctor or nurse talk about your absolute neutrophil count or ANC. This is the number of neutrophils you have in a certain amount of blood. Your health care team will use your ANC to get an idea of how well your immune system might work during treatment. You might want to keep track of your ANC so you’ll know when you have a higher risk of getting an infection.

Some labs put this number on your complete blood count (CBC) report, but it isn’t always labeled “ANC,” so you may need to ask your doctor or nurse for help finding it. Sometimes the lab will only report different types of neutrophils as a percentage of white blood cells, and then your health care team will calculate your ANC. You can also calculate it yourself.

Figuring out your ANC

The numbers for your ANC are taken from the results of a blood test called the differential white blood cell (WBC) count. You can ask about the results of your blood tests or get copies of your test results from your doctor or nurse.

To find out your ANC, multiply the percentage of neutrophils by the total number of WBCs. (Neutrophils are sometimes called segs or polys, and young neutrophils may be called bands on your lab report. If bands are listed as a percentage of WBCs, add them to the neutrophils before multiplying.)

You can figure out your ANC using this formula:

    [(% of neutrophils + % of bands) ÷ 100] × WBC count = ANC

So, for example, if a patient’s WBC count is 2,000, with 65% neutrophils and 5% bands, then the ANC is 1,400, which is calculated like this:

    ANC = [(65 + 5) ÷ 100] × 2,000

    ANC = (70 ÷ 100) × 2,000

    ANC = 0.7 × 2,000 = 1,400

What does the ANC mean?

An ANC of less than 1,000 means that you have a low number of neutrophils and your immune system is weak. Ask your doctor or nurse to tell you exactly what your numbers mean.

The lower the ANC drops and the longer it stays low, the higher your risk of getting a serious infection. If the ANC drops below 500 for a few days, you are at a very high risk of getting an infection. If your ANC is 100 or less for more than a week, your risk of serious infection is extremely high.

In a person with a healthy immune system, the usual signs of infection are fever, pus, pain, swelling, and redness. As the ANC gets lower, many of these signs may not show up when an infection starts. This is because these signs are caused by neutrophils fighting off germs, and you don’t have enough neutrophils to produce the signs. This can make it hard to know if you have an infection. The good thing is that another WBC, called the monocyte, can still cause fever in the person who has neutropenia. In people with severe neutropenia, a fever may be the only sign of an infection.

If your ANC is 1,000 or lower and you have a fever of 100.5° F (38° C) or higher when taken by mouth, your doctor will likely assume that you have an infection. Antibiotic treatment is usually started right away, often before the cause of the infection can even be found. Until they can pinpoint the exact bug, doctors learn what they can about the infection to narrow down the treatment options. But they still look for the exact cause so that they can choose the treatment that’s most likely to work – even if it means changing to different antibiotics than what they started with.

See Causes (Germs) and Treatment of Infections in People with Cancer to learn more about this.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: February 16, 2015 Last Revised: February 10, 2017