High White Blood Cell Count: Not Just Bacterial Infection—Full Differential

Leukocytosis (WBC >11,000/µL) is nonspecific. While bacterial infection is a common cause, many other conditions elevate WBC:

Broad Differential

• Infections: Viral (lymphocytosis), fungal, parasitic, TB.
• Inflammatory/autoimmune: RA, SLE, vasculitis, IBD, Kawasaki.
• Allergic/hypersensitivity: Eosinophilia (asthma, atopy, drug reaction, helminths).
• Stress responses: Surgery, trauma, burns, acute MI, DKA—demargination of neutrophils.
• Medications: Corticosteroids (neutrophilia), lithium, G-CSF, epinephrine.
• Hematologic malignancies: Leukemia (blasts), lymphoma, myeloproliferative neoplasms.
• Asplenia/hyposplenism: Loss of splenic sequestration.
• Pregnancy/labor: Physiologic neutrophilia.

Diagnostic Approach

1. Differential count (neutrophils, lymphocytes, eosinophils, monocytes, basophils).
2. Peripheral smear review (blasts, toxic granulation, atypical lymphs).
3. Clinical correlation: fever, focal signs, exposure history, medication list.
4. Targeted workup: cultures, imaging, flow cytometry, bone marrow if indicated.

Isolated leukocytosis without left shift or symptoms often resolves with observation. Never treat the number alone.