High concentrations of neutrophils or heterophils are usually indicative of what disease or condition?

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

Answer: (A)

High neutrophil or heterophil counts indicate an active bacterial infection because these cells are the body's rapid responders to bacterial invasion. When bacteria enter the body, chemical signals recruit neutrophils to the site of infection, where they phagocytose bacteria and release antimicrobial substances. This acute inflammatory response drives an increase in circulating neutrophils as the bone marrow releases stores and ramps up production.

In contrast, viral infections usually cause a rise in lymphocytes rather than neutrophils; parasitic infections often lead to eosinophilia; and allergic reactions typically involve eosinophils and other mediators rather than a neutrophil-dominant response.