Neutrophilia with a left shift is most commonly associated with which condition?

• A. A parasitic infection
• B. A bacterial infection
• C. A viral infection
• D. An allergic reaction

Answer: (B)

Neutrophilia with a left shift indicates an acute bacterial infection. When bacteria invade, the body ramps up production of neutrophils in the bone marrow and releases them into the bloodstream. If the demand is high, immature neutrophil forms (bands) spill into circulation, shifting the differential to the left. This pattern—high neutrophils with a notable number of immature forms—is a classic response to bacterial pathogens and early inflammation, and it often accompanies sepsis.

Viral infections, by contrast, more often cause a relative rise in lymphocytes rather than neutrophils, and they don’t typically produce a left shift. Allergic reactions tend to involve eosinophils and basophils rather than a neutrophil-dominated left shift, and parasitic infections more commonly elevate eosinophils as well.