what is rdw in blood test

The Red Cell Distribution Width (RDW) is a blood test that measures the variation in size and volume of red blood cells (erythrocytes) . Normally, red blood cells are all about the same size, but a high RDW means that there is a major difference between the size of the smallest and largest red blood cells. This may be a sign of a medical condition, such as anemia, a condition in which your red blood cells cant carry enough oxygen to the rest of your body. The RDW test is often part of a complete blood count (CBC), which measures many different parts of your blood, including red cells. The RDW test is commonly used to help diagnose anemia and determine its cause. The test is performed by drawing a blood sample from a vein, usually from the inside crook of your elbow or the top of your hand, and the analyzed blood serves as a representative sample to better understand variations in red blood cell size throughout your body. RDW is usually reported as a percentage that describes the amount of variability in the size of RBC, and the RDW result is interpreted by comparing it to a reference range established by the laboratory conducting the test.