What is a red cell distribution width test?A red cell distribution width (RDW) test is a measurement of the range in the volume and size of your red blood cells (erythrocytes). Red blood cells move oxygen from your lungs to every cell in your body. Your cells need oxygen to grow, reproduce, and stay healthy. If your red blood cells are larger than normal, it could indicate a medical problem.Other names: RDW-SD (standard deviation) test, Erythrocyte Distribution Width
