The Red Cell Distribution Width (RDW) test is a component of a complete blood count (CBC), a routine blood test providing insight into overall health. This measurement evaluates the uniformity of red blood cells, which transport oxygen throughout the body, helping healthcare professionals assess their characteristics.
Understanding RDW
RDW measures the variation in the size and volume of your red blood cells (RBCs). Red blood cells normally maintain a relatively consistent size, typically ranging from 6.2 to 8.2 micrometers in diameter. A “normal” RDW result, usually between 11.5% and 15% in adults, indicates that your red blood cells are uniform in size. This uniformity is important because the size of red blood cells can affect their ability to efficiently deliver oxygen to the body’s tissues and organs.
What a High RDW Indicates
A high RDW signifies increased variability in red blood cell size, a condition called anisocytosis. This means a wider range exists between the smallest and largest red blood cells in your blood sample. While a high RDW points to this variation, it is not a diagnosis on its own, but a clue for further investigation into an underlying health condition.
Common Causes of Elevated RDW
An elevated RDW often signals that the body is producing red blood cells of different sizes. Nutritional deficiencies are frequent culprits; for example, iron deficiency anemia typically leads to smaller red blood cells, while vitamin B12 or folate deficiencies result in larger cells. These deficiencies increase the variation in red blood cell size, which can be an early indicator even before other red blood cell parameters change.
Chronic inflammatory conditions can also elevate RDW, as inflammation disrupts the normal production and lifespan of red blood cells in the bone marrow, leading to varied sizes. Liver disease is another factor that can cause a high RDW, potentially due to its impact on red blood cell production and the health of circulating cells.
Kidney disease is frequently associated with an elevated RDW, often due to impaired red blood cell production and increased destruction of existing cells. Additionally, certain cancers, such as colorectal cancer, and heart disease have been linked to higher RDW values, possibly due to chronic inflammation or other systemic effects on red blood cell dynamics.
Next Steps After a High RDW Result
The most important next step after a high RDW result is to consult a healthcare professional for a comprehensive evaluation. They will consider your RDW result in conjunction with other parameters from your complete blood count, such as mean corpuscular volume (MCV), to gain a clearer picture.
Additional tests may be necessary to pinpoint the exact cause of the elevated RDW. These might include iron studies, vitamin B12 and folate levels, or further blood counts to assess other red blood cell characteristics. A high RDW is a piece of a larger diagnostic puzzle, providing a valuable clue that helps guide further investigation rather than serving as a standalone diagnosis. Self-diagnosing based solely on an RDW result is not recommended, as proper interpretation requires professional medical assessment.