Red Cell Distribution Width

RDW stands for red cell distribution width (sometimes written erythrocyte distribution width). It measures how much your red blood cells vary in size — a low RDW means they're uniform, a high RDW means there's a wide mix of small and large cells. It's reported as a percentage and often rises early in nutritional anemias before other markers move.

RDW quantifies the variation (spread) in red-cell size. The normal range is roughly 11.5–14.5%. A rising RDW signals that your marrow is producing cells of uneven size, which often happens as a deficiency develops or as an anemia recovers and new, differently sized cells enter circulation.

Both are above the ~14.5% top of the normal range. 14.8% is only mildly elevated and, on its own, is often not concerning. 16% is more clearly high and usually prompts a look at iron, B12, and folate, especially alongside an abnormal MCV — high RDW with low MCV classically points to iron deficiency. Interpret it together with your other red-cell numbers.

A low RDW (for example 11.8%, at or just below the bottom of the range) means your red cells are unusually uniform in size. This is generally not clinically significant and isn't a cause for concern on its own — unlike a high RDW, a low value rarely points to a specific problem.

Not directly. Testosterone raises red-cell production (hematocrit and hemoglobin) but doesn't inherently widen the size distribution. RDW is still useful on TRT because it can catch a subtle iron deficiency — for instance from frequent blood donation to manage high hematocrit — before hemoglobin or MCV clearly change.