White Blood Cell Count

This test measures the total number of white blood cells in your bloodstream. White blood cells, also called leukocytes, are immune cells that help your body fight infections and heal from injury. The count reflects all major types of white cells together, such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

It is usually performed as part of a complete blood count from a standard blood draw. Results give a snapshot of how active your immune system is and can prompt further testing, such as a differential that breaks down the types of white cells if needed.

Your white blood cell count helps your care team evaluate possible infection, inflammation, allergic reactions, stress responses, and bone marrow function. A higher count can be seen with bacterial infections, some medications, smoking, or physical stress, while a lower count can occur with certain viral illnesses, autoimmune conditions, some medicines, vitamin deficiencies, or bone marrow disorders.

Clinicians order this test when you have symptoms like fever, sore throat, cough, or fatigue, before surgeries or procedures, and to monitor treatments that affect the immune system, including chemotherapy, immunosuppressants, or medicines known to influence white cells.

Interpreting your result depends on your symptoms, medical history, medications, and sometimes the breakdown of white cell types. A single unexpected result may be rechecked, because white counts can change during the day, with stress or exercise, or with minor illnesses. Your clinician may order a differential count, a smear review, or repeat testing to confirm patterns and look for the underlying cause.

If your count is lower than expected, your clinician may discuss ways to reduce infection risk, review medications, and consider additional tests. If your count is higher than expected, they may check for infection, inflammation, medication effects, or other causes. Seek prompt medical care if you have warning signs such as fever, chills, shortness of breath, chest pain, or rapidly worsening symptoms.