What Does High WBC in a Blood Test Mean?

High WBC (above 11,000/µL) is called leukocytosis. It usually indicates your immune system is actively fighting something.

Common Causes

• Bacterial infection — most common
• Inflammation — autoimmune disease, IBD
• Physical stress — exercise, surgery, trauma
• Corticosteroid medications
• Leukemia — markedly elevated (above 30,000)

When Is It Concerning?

• Above 30,000 — possible leukemia or severe infection
• With fever and left shift — active bacterial infection
• Persistently elevated without obvious cause — investigate