RDW-SD

Red Cell Distribution Width - Standard Deviation (RDW-SD) measures the variation in red blood cell size based on the actual width of the size distribution curve (in femtoliters, fL). Unlike RDW-CV (%), RDW-SD is not affected by the MCV. Increased RDW-SD indicates greater variation in RBC size (anisocytosis), similar to RDW-CV.