Which blood cell type, when decreased, is associated with increased infection risk?

• A. Neutrophils
• B. Erythrocytes
• C. Thrombocytes
• D. Eosinophils

Answer: (A)

When neutrophils are decreased, infection risk rises because they are the body's frontline defenders in the innate immune system. These cells are the first responders to bacterial and fungal invaders, rapidly arriving at infection sites to engulf and destroy pathogens (phagocytosis) and to release substances that kill microbes. A lower neutrophil count—neutropenia—weakens this rapid, initial defense, making it easier for infections to take hold and progress, which is a major concern in patients whose bone marrow is suppressed by treatment or disease.

Erythrocytes are red blood cells that carry oxygen; a decrease causes fatigue and anemia, not a direct increase in infection risk. Thrombocytes are platelets involved in blood clotting; their decrease leads to bleeding problems, not typically infections. Eosinophils defend against parasites and participate in allergic responses; their reduction does not have the same broad impact on infection risk as neutrophils.