What is the normal red cell distribution width (RDW) range, and what does an RDW above 22% indicate?

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Multiple Choice

What is the normal red cell distribution width (RDW) range, and what does an RDW above 22% indicate?

RDW measures variation in red blood cell sizes (anisocytosis). In healthy adults it’s typically about 11.5% to 14.5%. When RDW rises past roughly 22%, the distribution of red cell sizes often becomes bimodal, showing two distinct populations of cells. This reflects a scenario where there are two different size groups—such as a mix of small microcytes with normal or larger cells—indicating a mixed or evolving process rather than a single uniform population. While RDW can be elevated in iron deficiency and other anemias, the key idea is that a very high RDW points to two populations rather than a single, homogeneous cell size.

RDW measures variation in red blood cell sizes (anisocytosis). In healthy adults it’s typically about 11.5% to 14.5%. When RDW rises past roughly 22%, the distribution of red cell sizes often becomes bimodal, showing two distinct populations of cells. This reflects a scenario where there are two different size groups—such as a mix of small microcytes with normal or larger cells—indicating a mixed or evolving process rather than a single uniform population. While RDW can be elevated in iron deficiency and other anemias, the key idea is that a very high RDW points to two populations rather than a single, homogeneous cell size.

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