- White blood cells help fight infections by attacking bacteria, viruses, and germs that invade the body.
- A WBC count can detect hidden infections and undiagnosed medical conditions.
- A healthcare provider or lab technician will draw blood to check your WBC count.
White blood cells (WBCs), also called leukocytes, are an important part of the immune system. These cells help fight infections by attacking bacteria, viruses, and germs that invade the body. White blood cells originate in the bone marrow, but circulate throughout the bloodstream. There are five major types of white blood cells:
A WBC count is a test that measures the number of white blood cells in your body. This test is often included with a complete blood count (CBC). Your blood contains a percentage of each type of white blood cell. Sometimes, however, your white blood cell count can fall or rise out of the healthy range.
It is normal for doctors to order a complete blood count and check your WBC count during an annual physical examination. Your doctor may recommend a WBC count if you complain of persistent body aches, fever, chills, or headaches. A WBC count can detect hidden infections within your body and alert doctors to undiagnosed medical conditions, such as autoimmune diseases, immune deficiencies, and blood disorders. This test also helps doctors monitor the effectiveness of chemotherapy or radiation treatment in cancer patients.
A healthcare provider or lab technician will draw blood to check your WBC count. This blood sample is taken either from a vein in your arm or a vein on the back of your hand. It only takes a couple of minutes to draw your blood and you may experience minor discomfort. The healthcare provider will clean the needle site to kill any germs and then tie an elastic band around the upper section of your arm. This elastic band helps the blood fill your vein, making it easier for the blood to be drawn.
The healthcare provider slowly inserts a needle into your arm or hand, and collects the blood in an attached tube. The provider then removes the elastic band from around your arm and slowly removes the needle. The technician will apply gauze to the needle site to stop the bleeding.
Healthcare providers use a different technique when drawing blood from young children and infants. With these patients, providers first puncture the skin with a lancet (a pricking needle) and then use a test strip or a small vial to collect the blood. Results are sent to a lab for review.
A WBC count requires no specific preparation. You simply schedule an appointment with your doctor or set up an appointment at a local medical laboratory. Certain medications can interfere with your lab results and either lower or increase your WBC count.
The drugs that may affect your test results include:
- chemotherapy medication
Prior to having your blood drawn, tell your doctor about all prescription and nonprescription medications that you’re currently taking.
An average normal range is between 4,500 and 10,000 white blood cells per microliter (mcL). Abnormal test results are classified by numbers that are higher or lower than this range. It’s important to note that age can also affect the number of white blood cells, with infants having a higher count than adults.
A low or high WBC count can point to a blood disorder or other medical condition. To identify the exact cause of a high or low WBC count, your doctor will take several factors into consideration, such as your list of current medications, symptoms, and medical history.
Leukopenia is the medical term used to describe a low WBC count. A low number can be triggered by:
- autoimmune disorders
- bone marrow disorders/damage
- severe infections
- liver and spleen diseases
- radiation therapy
Leukocytosis is the medical term used to describe a high WBC count. This can be triggered by:
- tumors in the bone marrow
- inflammatory conditions, such as arthritis and bowel disease
- tissue damage
After diagnosing the cause of a high or low WBC count and recommending a treatment plan, doctors will periodically recheck your white blood cells. If your white blood cell count remains high or low, this can indicate that your condition has worsened. Your doctor may adjust your treatment. If your WBC count shows a normal range, this usually indicates that the treatment is working.
Having your blood drawn is a simple procedure, and complications are extremely rare. It can be difficult to take blood from people with small veins. The lab technician may be unable to locate a vein, or once the needle is inside the arm or hand, they may have to move the needle around in order to draw blood. This can cause a sharp pain or a stinging sensation. Rare complications include:
- infection at the needle site
- excessive bleeding
- lightheadedness or fainting
- bleeding underneath the skin (hematoma)