Chemotherapy, radiation therapy, surgery, stem cell transplant, bone marrow transplant, steroids, or the cancer itself can suppress or weaken the immune system. This is called immunosuppression. These treatments can lower the number of white blood cells (WBCs) and other immune system cells.
You may get an infection when there aren’t enough WBCs, especially neutrophils, to destroy germs. Treatment can also cause these cells to not work as well as they should.
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 normal while you are neutropenic. But in most cases the WBC count is low when the neutrophil count is low.
Absolute neutrophil count
You may 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 this number to get an idea of how well your immune system is working while you’re getting 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 will put this number on their report, or you can ask the nurse to help find it. 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 find out the results of these blood tests or get copies of the test results from your doctor.
Normally, neutrophils make up 50% to 70% of WBCs. 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 1,000 and the percentage of neutrophils is 70%, and there are no bands, then the ANC is 700, which is calculated like this:
[(70 + 0) ÷ 100] × 1,000
(70 ÷ 100) × 1,000
0.7 × 1,000 = 700
Another example is if the patient’s WBC is 1,300, with 60% neutrophils and 5% bands. The bands are added with the neutrophils (60 + 5), and the ANC is 845:
[(60 + 5) ÷ 100] × 1,300
(65 ÷ 100) × 1,300
0.65 x 1300 = 845
What the absolute neutrophil count means: An ANC less than 1,000 means that you have a low number of neutrophils and your immune system is weak.
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 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. So if you’re neutropenic, you might not have enough neutrophils to show signs the body is fighting back, even though the germs are there. 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.
Last Revised: 12/06/2012