The Red Cell Distribution Width (RDW) is a measurement frequently found on a complete blood count (CBC), a common blood test. It provides insights into the variation in size of your red blood cells. This article explores what RDW signifies, how its results are interpreted, and its medical implications.
Understanding RDW
RDW, or Red Cell Distribution Width, quantifies the variation in the size and volume of your red blood cells. Healthy red blood cells are uniform in size, typically ranging from 6.2 to 8.2 micrometers. When there is a significant difference in their sizes, a condition known as anisocytosis occurs. It is part of the red blood cell indices in a CBC, automatically calculated by laboratory equipment.
The RDW value reflects the spread of red blood cell sizes on a histogram, a graph that illustrates the range of cell sizes. If red blood cells are mostly the same size, they cluster closely together on the histogram, resulting in a lower RDW. Conversely, a wide spread of sizes indicates a higher RDW. This measurement assesses red blood cell uniformity, which supports their efficient oxygen transport.
Interpreting Your RDW Results
RDW results are presented as a percentage, indicating red blood cell deviation from an average size. A normal RDW typically falls within 12% to 15%, though this can vary between laboratories. A result within this normal range suggests that your red blood cells are relatively uniform in size. However, a normal RDW does not rule out an underlying health condition, as some conditions can present with a normal RDW but abnormal values in other red blood cell parameters.
A high RDW indicates greater variation in red blood cell size, meaning they are less uniform. This can signal the body is producing red blood cells of different sizes, pointing to various underlying issues. Conversely, a low RDW means minimal variation in red blood cell size and is generally not a concern. RDW results are always interpreted alongside other CBC parameters, such as Mean Corpuscular Volume (MCV), which measures average red blood cell size, for a comprehensive picture.
Medical Implications of RDW
An abnormal RDW, especially a high RDW, can indicate several medical conditions. It is associated with various types of anemia, characterized by an insufficient number of healthy red blood cells. For instance, a high RDW can help differentiate between iron deficiency anemia, where red blood cells may be smaller, and megaloblastic anemias, such as those caused by vitamin B12 or folate deficiencies, where red blood cells can be larger. In iron deficiency, RDW often increases before other red blood cell indices change, serving as an early diagnostic clue.
Beyond anemias, an elevated RDW can link to nutritional deficiencies, including vitamin B12 and folate. Chronic diseases like liver disease, kidney disease, heart disease, and diabetes may also associate with a high RDW. An elevated RDW can suggest underlying inflammation or issues with red blood cell production and lifespan. It serves as a diagnostic tool, prompting further investigation and guiding medical consultations.