Red Cell Distribution Width (RDW) measures how much variation exists in the size of your red blood cells with a typical range of ~11–15%. While traditionally used to help classify anemia, RDW has emerged as a broader marker of physiologic stress. Higher RDW levels—even within the normal range—have been associated with increased risk of cardiovascular disease and all-cause mortality. This likely reflects underlying processes such as inflammation, oxidative stress, or suboptimal nutrient status.