Elevated White Blood Cell Count (Leukocytosis): Causes and When to Worry

Leukocytosis (WBC >11,000/µL) usually signals an immune response.

Common Causes

1. Infections (bacterial, viral, fungal, parasitic)
2. Inflammation (arthritis, IBD, colitis)
3. Severe allergies/anaphylaxis
4. Leukemia (malignant proliferation)
5. Severe physical/emotional stress
6. Pregnancy (physiologic rise)
7. Corticosteroids, lithium, other drugs

Associated Symptoms

Fever, chills, fatigue, myalgias, headache, anorexia, lymphadenopathy, skin abscesses.

When to Investigate

Persistent elevation without clear infection, or with concerning symptoms (weight loss, night sweats, bruising), requires hematology workup.