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 is possible for your total WBC count to be normal while you are still 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 are getting treatment. You might want to keep track of your ANC so you will know when you are at a higher risk of getting an infection. Some labs will figure up this number on their report, or you can ask the nurse for help with it. You may 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. You may have to ask the doctor or nurse what the different numbers are on the lab report before you start figuring out your ANC.
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 there are bands listed as a percentage of WBCs, those are added 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 for 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, most 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 may 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.
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 the fever is caused by an infection. Treatment with antibiotics is usually started right away, often before the cause of the infection can even be found. When a person has neutropenia, infections must be treated as quickly as possible. But doctors still look for the cause so that they can be sure that the treatment they’re giving will take care of it.
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