A high red cell distribution width is not an indication of dehydration. It is a measure of the variability of the size of red blood cells, notes Lab Tests Online. A high value indicates high variability in red blood cell size, while a low value indicates uniformity in cell size.
A high RDW indicates a mixed population of large and small red blood cells, typically caused by the presence of immature red blood cells, which are larger compared to mature red blood cells, according to Lab Tests Online. This can be caused by conditions such as iron-deficiency anemia or pernicious anemia.