Which WBC differential finding most indicates infection?

• A. Leukocytosis with neutrophilia
• B. Eosinophilia with basophilia
• C. Leukopenia with lymphocytosis
• D. Thrombocytosis

Answer: (A)

Infection, especially bacterial, typically triggers an increase in white blood cells with a shift toward neutrophils. A leukocytosis (high WBC count) with neutrophilia (a higher proportion of neutrophils) reflects the body’s immediate response to bacterial invasion, as neutrophils are the first responders that engulf and destroy bacteria. A left shift, with more immature neutrophils, may also occur as the bone marrow releases cells to meet the demand.

The other patterns don’t fit the usual infection signal: eosinophilia with basophilia points more toward allergic reactions or parasitic infections; leukopenia with lymphocytosis suggests viral infection or bone marrow suppression rather than a typical acute bacterial infection; thrombocytosis involves platelets and is not a direct indicator of bacterial infection in the white blood cell differential.