Final answer:
RDW-CV calculates red blood cell variation as a percentage, using the standard deviation divided by the mean corpuscular volume and then multiplied by 100%. RDW-SD measures the actual variation in red blood cell size distribution in volume units and is examined through blood analyzers.
Step-by-step explanation:
The RDW-CV formula, which stands for Red Cell Distribution Width-Coefficient of Variation, is calculated using the standard deviation (SD) of red blood cell (RBC) volume divided by the mean corpuscular volume (MCV) of the RBCs, then multiplied by 100 to convert to a percentage. The formula appears as RDW-CV = (Standard Deviation of MCV / Mean MCV) × 100%. To determine RDW-SD, or Red Cell Distribution Width-Standard Deviation, one must measure the actual width in volume units (fL) of the distribution curve of red blood cell sizes. This measurement reflects the variation in RBC size and is not directly calculated from other RBC indices, but rather through specialized automated blood analyzers that evaluate the size distribution of erythrocytes.