Moderate White Blood Cell Elevation: Causes and Clinical Approach

Definition

Leukocytosis: WBC >11,000/µL. "Moderate" typically 11,000–30,000/µL. Levels >30,000 suggest leukemia or leukemoid reaction.

Common Causes

Category	Examples
Infection	Bacterial (neutrophilia), viral (lymphocytosis), TB, fungal
Inflammation	Rheumatoid arthritis, IBD, vasculitis, post-surgical
Stress/Drugs	Corticosteroids (demargination), epinephrine, G-CSF, lithium
Hematologic	CML, CLL, leukemoid reaction, myeloproliferative neoplasms
Other	Smoking, obesity, asplenia, pregnancy

Evaluation

1. Differential count (neutrophils vs. lymphocytes vs. eosinophils)
2. Peripheral smear (blasts? toxic granulation? Döhle bodies?)
3. Clinical context (fever, symptoms, medications, chronic conditions)
4. Trend (acute vs. chronic)
5. If persistent or unexplained: flow cytometry, BCR-ABL, JAK2, bone marrow biopsy

Clinical Pearls

• Corticosteroids → neutrophilia + lymphopenia + eosinopenia
• Left shift (bands >10%) = bacterial infection
• Eosinophilia >500: allergy, parasites, drugs, eosinophilic disorders
• Lymphocytosis: viral, pertussis, CLL

When to Refer

Persistent >30,000, blasts on smear, constitutional symptoms, organomegaly, cytopenias → hematology referral.