White Blood Cell Count (WBC)

What is White Blood Cell Count (WBC)?

WBC count measures the total number of white blood cells (leukocytes) in your blood, the immune system's frontline defense cells.

White blood cells are produced in the bone marrow and circulate through blood and tissue to fight infection, respond to inflammation, and clear damaged cells. The WBC count is a total of five different cell types (neutrophils, lymphocytes, monocytes, eosinophils, basophils), each with a distinct immune role. A high count often reflects the body actively responding to infection, inflammation, or stress, while a low count can mean reduced infection-fighting capacity or a bone marrow issue. It's one of the most commonly ordered screening values on a standard CBC.

Tests often checked alongside this

• WBC Differential (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils) — identifies which specific cell type is driving an abnormal total count
• C-Reactive Protein (CRP) — helps confirm whether inflammation or infection is present alongside a WBC change
• Erythrocyte Sedimentation Rate (ESR) — another inflammation marker often checked together with WBC when infection or inflammation is suspected
• Absolute Neutrophil Count (ANC) — important when WBC is low, to assess infection risk

How this can show up in how you look and feel

• Frequent or lingering infections, fevers, or slow-healing wounds are sometimes associated with a low WBC count
• Fatigue or general malaise can accompany either very high or very low readings, often tied to the underlying cause rather than the number itself
• Unexplained fever or chills may accompany an elevated WBC driven by infection
• Many people with mildly abnormal WBC counts feel completely normal — this is often an incidental finding

What can affect this marker

• Acute infection (bacterial, viral, or fungal) — typically raises WBC, especially neutrophils
• Physical or emotional stress, and intense/prolonged exercise — can cause a temporary rise
• Smoking — chronically elevates WBC through ongoing inflammatory processes
• Bone marrow disorders or immune-suppressing conditions/treatments — can lower WBC by reducing production

What to track over time

• Whether an elevated or low reading is a one-time event (e.g., during an illness) or a persistent pattern across multiple tests
• Trend direction over time relative to your own personal baseline, not just the population range
• Whether changes track with known triggers (recent infection, new medication, intense training block)
• How WBC moves together with the differential (neutrophils, lymphocytes) rather than looking at the total number alone

What to ask your doctor

• Is my WBC count outside the range because of an infection, stress, or something that needs further workup?
• Should I get a differential (breakdown by cell type) to understand which white cells are driving this result?
• Do any of my current medications affect white blood cell production?
• How often should I recheck this if the result is borderline or new?

This glossary entry is for informational purposes only and is not a substitute for professional medical advice. Read our Terms of Use.