Which statement about absolute neutrophil count (ANC) is true?

• A. ANC is diagnostic to diagnose leukemia.
• B. An ANC less than 500 indicates a high risk for infection.
• C. Patients with aplastic anemia will show high ANC level.
• D. Chemotherapy selection is based on the ANC.

Answer: (B)

Low neutrophil counts elevate infection risk because neutrophils are the primary defense against bacteria and fungi. The absolute neutrophil count (ANC) estimates how many neutrophils are circulating and is calculated as ANC = total WBC × (fraction of neutrophils and bands). Normal ANC is roughly 1,500 to 8,000 per microliter; when the ANC falls below 1,000, the risk rises, and severe neutropenia is typically defined as ANC less than 500. In this range, the body's ability to mount an adequate inflammatory response is blunted, so even minor infections can progress rapidly, and fever in a neutropenic patient is treated as a medical emergency. This makes the statement that an ANC below 500 indicates a high risk for infection the correct one. The other points aren’t accurate: the ANC by itself does not diagnose leukemia; aplastic anemia involves low counts including neutrophils rather than a high ANC; and chemotherapy decisions rely on multiple factors beyond the ANC, such as marrow reserve, performance status, organ function, and treatment nadir expectations.