A Red Cell Distribution Width (RDW) test is a component of a common blood panel known as a Complete Blood Count (CBC). This test measures the variation in the size and volume of your red blood cells. Red blood cells are essential for carrying oxygen throughout the body. Understanding what a low RDW result indicates can provide insights into your overall health, though it is rarely interpreted in isolation.
Understanding Red Cell Distribution Width
The RDW test determines how uniform your red blood cells are in size. Red blood cells typically maintain a consistent size, generally between 6.2 and 8.2 micrometers. The RDW value is presented as a percentage, reflecting the degree of variation in cell volume.
A normal RDW range typically falls between 12% and 15%, varying slightly by laboratory. This range suggests red blood cells are relatively uniform. Anisocytosis refers to variations in red blood cell size, which RDW quantifies.
Interpreting a Low RDW Result
A low RDW indicates your red blood cells are more uniform than average, with less variation in volume and diameter. They are consistently sized, clustering closely when analyzed. Unlike a high RDW, which often signals underlying issues like anemia, a low RDW is generally less common and concerning.
A low RDW alone is typically not a sign of anemia or immediate worry. It signifies red blood cell homogeneity, common in healthy individuals. However, a low RDW can sometimes be observed in specific conditions where red blood cells are uniformly small or uniformly large.
For instance, in microcytic anemias like thalassemia minor, red blood cells are uniformly smaller, resulting in a low or normal RDW. Thalassemia, a genetic blood disorder, produces less hemoglobin, leading to smaller, consistently sized red blood cells. This contrasts with iron deficiency anemia, where red blood cell sizes can vary significantly, often leading to a high RDW.
Similarly, some macrocytic anemias, with uniformly larger red blood cells, might also present a low RDW. While often associated with vitamin B12 or folate deficiencies (leading to high RDW due to varied cell sizes), certain non-megaloblastic macrocytic anemias (not caused by impaired DNA synthesis) can show a low RDW. Here, cells are consistently large, leading to less variation.
A low RDW is rarely a standalone diagnostic marker. Healthcare providers evaluate it with other Complete Blood Count parameters, especially Mean Corpuscular Volume (MCV), which measures average red blood cell size. This combined assessment provides a more comprehensive picture of red blood cell health and helps differentiate between various conditions.
When to Consult a Healthcare Provider
Always discuss any abnormal lab results, including a low RDW, with a healthcare provider. A low RDW is interpreted within your entire blood panel, overall health, and any symptoms. The significance of a low RDW can vary greatly depending on these other factors.
Your doctor considers RDW alongside other red blood cell indices like MCV, Mean Corpuscular Hemoglobin (MCH), and Mean Corpuscular Hemoglobin Concentration (MCHC) for a complete understanding. They also review your medical history, family history of blood disorders, and current symptoms. This comprehensive approach helps determine if the low RDW is an isolated finding, a natural variation, or indicates an underlying condition needing further investigation.
If necessary, your healthcare provider might order additional tests to clarify the cause or rule out concerns. They can also provide reassurance if the result is not clinically significant. Avoid self-diagnosing based solely on a single lab value; professional medical interpretation is essential for accurate assessment and appropriate guidance.