High RDW, or red cell distribution width, is sometimes caused by liver disease, according to Medscape.com. In this case, the mean corpuscular volume, or MCV, is also elevated. These test results are possible indicators of hemolytic anemia, a condition where red blood cells are wiped out too soon.
On occasion, increased RDW and MCV levels signal a deficiency in B12, or folic acid. However, if the RDW is high and MCV is low, iron-deficiency anemia is a possibility. This high-low relationship also suggests thalassemia intermedia, a blood-production disorder. A high RDW accompanied by a normal MCV reading sometimes indicates the start of a problem, such as a deficiency in iron, B12 or folic acid.