How is the red blood cell distribution width (RDW) calculated?

The red blood cell distribution width (RDW) is calculated using the mean corpuscular volume (MCV) and the red blood cell (RBC) count. RDW indicates the variation in the size of red blood cells in a given sample; a higher RDW suggests a greater variability in red cell sizes, which can be an important indicator in diagnosing various types of anemia and other medical conditions.

The calculation involves measuring the standard deviation of red blood cell volumes and then normalizing this value against the MCV. This method quantifies the range of red blood cell sizes, providing useful diagnostic information beyond just the average size represented by MCV alone.

The options that rely on hemoglobin and hematocrit values, direct microscopic observation, or patient symptoms and history do not directly pertain to the mathematical calculation specifically associated with RDW. They might offer some context for broader diagnostic considerations but do not contribute to the actual calculation of RDW. Thus, focusing solely on MCV and RBC values gives the correct basis for determining RDW.