"RDW-CV" and "RDW-SD" are a measurement of the size of red blood cells, according to Med-Health.net. RDW-SD is an actual measurement, while RDW-CV involves some calculations using the RDW-SD deviation.
Coupled with the MCV, the mean corpuscular volume, these numbers can indicate the patient's state of health, notes Med-Health.net. For example, if RDW is normal, but the MCV is low, the patient could be anemic. If the RDW is normal, but the MCV is high, the patient could have something more serious, such as chronic liver disease. If both are high, it could indicate any number of things, including low vitamin b12, liver problems or diseases such as myelodysplastic syndrome.