Inother words, no problem! RDW refers to the variation in size if your red blood cells. A … low RDW means that the cells are all roughly the same size. A high RDW means there isa high variation in the sizes of the cells and usually means a deficiency of iron and/or B12.f the RDW level is increased and the MCV level is normal. This can be caused by the beginning stages of a decrease in vitamin B12 or folic acid (a type of vitamin) in the body. It can also be caused by the beginning stages of iron deficiency anemia.