Red Cell Distribution Width (RDW) is a measurement found in a standard Complete Blood Count (CBC) blood test. It assesses the variability in the size of your red blood cells, providing insight into how uniform or varied these oxygen-carrying cells are within your bloodstream. RDW is a fundamental part of a routine check, offering an initial look at red blood cell health.
Understanding Red Blood Cell Variation
Red blood cells are typically uniform in size. When there is a significant variation in their size, this condition is known medically as anisocytosis. Measuring this variation can be an early indicator of underlying health issues.
The RDW quantifies this size variability. A higher RDW value indicates a greater degree of anisocytosis, meaning the red blood cells vary significantly in size. Conversely, a lower RDW suggests that the red blood cells are more uniform in size. This measurement provides a numerical representation of how consistent the red blood cell population is.
What Your RDW Results Indicate
A normal RDW range generally falls between 11.5% and 14.5%, though these values can vary slightly by laboratory. An elevated RDW indicates greater variation in red blood cell size.
This finding can be associated with several medical conditions. For instance, iron deficiency anemia often presents with a high RDW, particularly when accompanied by a low Mean Corpuscular Volume (MCV), which measures the average size of red blood cells. Conversely, vitamin B12 or folate deficiencies can also lead to an elevated RDW, but these are typically seen with a high MCV.
Other conditions that might show an increased RDW include some types of thalassemia, myelodysplastic syndromes, chronic liver disease, and kidney disease. Chronic inflammation can also contribute to an increased RDW. A low RDW is uncommon and usually does not carry significant clinical implications on its own.
RDW is not a specific diagnostic tool but a general marker. An abnormal RDW result must always be interpreted with other blood test results, especially MCV, Mean Corpuscular Hemoglobin (MCH), and Mean Corpuscular Hemoglobin Concentration (MCHC), as well as your overall clinical picture and medical history.
Next Steps and Further Evaluation
If your RDW result is outside the normal range, it is important to consult with a healthcare professional. An abnormal RDW is not a diagnosis in itself; rather, it serves as an indicator that further investigation may be necessary to determine the underlying cause of the red blood cell size variation. Your doctor will interpret this result within the context of your entire Complete Blood Count and other relevant health information.
The RDW is often used in combination with other parameters, particularly the Mean Corpuscular Volume (MCV), to help narrow down potential diagnoses. For example, a high RDW combined with a low MCV strongly suggests iron deficiency anemia, while a high RDW paired with a high MCV often points towards a vitamin B12 or folate deficiency. This combined interpretation helps guide the diagnostic process.
Based on these initial blood test results, your doctor may recommend additional, more specific tests. These could include ferritin levels to assess iron stores, direct measurements of vitamin B12 and folate levels, or tests to evaluate liver and kidney function. A comprehensive understanding of your medical history, a thorough physical examination, and all laboratory results are crucial for arriving at an accurate diagnosis and developing an appropriate treatment plan.