A high RDW value indicates there is a mix of small and large cells in a blood sample, explains the American Association for Clinical Chemistry. RDW stands for red blood cell distribution width, a measure of how much the red blood cells vary in size.
RDW is one of the measurements recorded during a complete blood count, notes the American Association for Clinical Chemistry. The complete blood count determines if a sample has a normal number of red blood cells, white blood cells and platelets. The test also determines the amount of hemoglobin, the percentage of red blood cells and the average size of the red blood cells in the sample. Two causes of an increased RDW are iron-deficiency anemia and pernicious anemia.