White Cell Count
Does this test have other names?
What is this test?
This test measures the number of white blood cells (WBCs) in your blood. Cells in your bone marrow make white blood cells and release them into the bloodstream to help you fight infection. White blood cells are part of your body's immune system, which keeps you healthy and makes you well when you get sick. White blood cells work to destroy any foreign virus, fungus, or bacteria that enter your body and threaten to make you sick.
When you get sick, your white blood cell count is higher than normal because your body is releasing more of these cells to fight the infection. But if you have certain illnesses like HIV or cancer, your white blood cell count can drop to very low levels. It can also drop if you are on medicine like chemotherapy that weakens your immune system.
White blood cells are divided into 5 major types:
This test measures the total count of all types of white blood cells. It does not measure the levels of individual types of white blood cells.
Why do I need this test?
You may need this test to find out if you have an infection or illness that is affecting your immune system. If your immune system is weakened by medicine or illness, you may also need this test to see if your white blood cell count is dangerously low. In that case, even a simple infection could be quite harmful because your body isn't able to defend itself.
What other tests might I have along with this test?
In addition to a white blood cell count, your healthcare provider may order a differential white blood cell count. This blood test measures the amount of each type of white blood cells. You may also need a complete blood count, or CBC, which measures all of the major blood cells, including white blood cells. A neutrophil test may be done to check for neutropenia. If you have neutropenia, it means your neutrophil count is low and you can easily get an infection.
Your healthcare provider may also collect and send samples of your blood, urine, sputum, and cerebral spinal fluid to the lab for bacterial and viral cultures. He or she may also order imaging tests to look for sources of infection. If your provider thinks you may have a certain type of blood cancer, you may need a biopsy and other tests help to figure out the cause of your abnormal WBC values.
What do my test results mean?
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.
Normal white blood cell counts are:
9,000 to 30,000/mm3 for newborns
6,200 to 17,000/mm3 for children under 2 years old
5,000 to 10,000/mm3 for children older than age 2 up to adults
Test results that are higher than normal may mean that you have an infection or illness that your body is fighting. Test results that are lower than normal may mean that your immune system isn't working as well as it should and that even a minor infection could cause serious health problems.
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your arm. Infants usually have one of their heels stuck with a needle to collect a few drops of blood.
Does this test pose any risks?
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
What might affect my test results?
Some medicines may affect your test results. Be sure your healthcare provider knows about treatments you are getting, medicines you are taking, or recent illnesses you've had.
How do I get ready for this test?
A blood test rarely requires any preparation. You can probably eat, drink, and take your medicine as usual, but check with your healthcare provider to be sure. Be sure your provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.