RDW stands for red blood cell distribution width. It is a measurement of the variation of the size of red blood cells found in a blood sample. A normal RDW value is between 10.2 and 14.5 percent.
If a blood test indicates a high RDW, analysts compare the RDW with the mean corpuscular volume, or MCV, the average amount of space occupied each blood cell. High RDW and MCV values can be caused by liver disease, a vitamin B12 deficiency or hemolytic anemia, a condition in which the body destroys red blood cells too early. High RDW values with low MCV values may be caused by a vitamin B6 deficiency, an iron deficiency, or a condition known as thalessemia intermedia, a blood disorder in which the ability to produce hemoglobin is impaired.
A RDW level that is below the normal range indicates that there is little variation in the size of the blood cells and is generally treated as clinically insignificant.