Which hematocrit value represents the typical threshold used to define anemia?

• A. 30%
• B. 35%
• C. 21%
• D. 40%

Answer: (C)

Hematocrit measures the proportion of blood volume occupied by red blood cells. Anemia occurs when red-cell mass is reduced enough to impair oxygen delivery to tissues. Normal ranges vary by age and sex, but exam-style thresholds are often simplified. In many NBME-style questions, a hematocrit around 21% is used as the cutoff for defining anemia because it represents a substantial reduction in red cells beyond normal variation. Values higher, such as 30%, 35%, or 40%, are closer to typical normal ranges or only indicate mild reductions. Therefore, 21% is the best marker for a clearly defined anemia in this context, signaling a clinically meaningful drop in red-cell mass.