RDW, an acronym for Red Cell Distribution Width, is a test that measures the variations in the size and volume of red blood cells (erythrocytes). Erythrocytes play a vital role by transporting oxygen from the lungs to body tissues, which is crucial for cellular energy production, growth, and overall health. Normally, red blood cells are similar in size. However, low or high RDW values in a blood test can indicate an underlying health issue.