A complete blood count (CBC) is a common laboratory test that provides a detailed look at the cells circulating in the blood. One specific measurement reported on this panel is the Red Cell Distribution Width, or RDW. Understanding the RDW is an important part of assessing overall blood health.
Understanding the RDW Measurement
The RDW is a calculated value that quantifies the variation in the size and volume of a person’s red blood cells. This measurement determines how uniform the red blood cells are in a sample, reflecting the body’s cell production process. If all the red blood cells are nearly identical in size, the RDW value will be low, indicating a highly homogeneous population.
A high RDW signals a greater spread in cell size, meaning there is a mix of both very small and very large red cells. This variation is typically expressed as a percentage on the lab report. The normal reference range for RDW is generally between 11.5% and 14.5%, though this range can vary slightly depending on the specific laboratory.
Interpreting a Low RDW Result
A result that falls below the established reference range is considered a low RDW. This finding is relatively uncommon and generally holds less clinical significance than an elevated RDW value. A low RDW simply means that the red blood cells are very consistent in size.
This uniformity is often considered a favorable result, as it suggests a stable and healthy production of red blood cells by the bone marrow. A low RDW is typically not associated with any specific type of anemia or blood disorder. In many cases, a low RDW can be observed in healthy individuals.
Sometimes, a temporarily low RDW may be noted following a recent blood transfusion, as donor cells introduce a highly uniform population. Because a low RDW indicates high uniformity, it rarely points to a major underlying medical condition requiring specific treatment. Diagnosis focuses much more often on high RDW values, which signify troubling cell size variation.
Assessing RDW with Other Blood Markers
The RDW is never evaluated in isolation; it is one component of the Complete Blood Count, and its interpretation relies heavily on other metrics. The most important marker to consider alongside RDW is the Mean Corpuscular Volume (MCV), which measures the average size of the red blood cells. The combined analysis of RDW and MCV is fundamental for diagnosing the specific cause of anemia.
If the RDW is low, the MCV value helps narrow down potential diagnoses for other concurrent blood issues by determining the average size of that uniform population. Any abnormal finding on a CBC should be discussed with a healthcare provider who can review the entire panel of results in the context of the patient’s overall health.