Red Cell Distribution Width (RDW) is a measurement often included in a routine blood test. The RDW value helps healthcare providers assess the uniformity of red blood cell sizes within your bloodstream.
What RDW Measures
Red Cell Distribution Width (RDW) quantifies the variation in the size of red blood cells. Healthy red blood cells typically maintain a relatively uniform size, but certain conditions can cause them to differ significantly in volume. This variation in cell size is known as anisocytosis.
The RDW measurement reflects the spread of red blood cell sizes around their average volume. A higher RDW value indicates a greater degree of anisocytosis, meaning there is a wider range of small and large red blood cells circulating in the blood. Conversely, a lower RDW suggests that the red blood cells are more uniform in size.
How RDW is Assessed
The RDW test is typically performed as a component of a Complete Blood Count (CBC). The assessment of RDW involves a straightforward blood draw, usually from a vein in your arm.
Generally, no special preparation, such as fasting, is required for an RDW test alone. However, if other blood tests are ordered concurrently as part of the CBC, specific preparation instructions might be necessary. Once collected, the blood sample is sent to a laboratory where automated analyzers measure and calculate the RDW value.
Interpreting RDW Values
The normal range for RDW can vary slightly between laboratories, but it is generally considered to be between 11.5% and 15.4%. A result within this typical range indicates that your red blood cells are relatively consistent in size. Even with a normal RDW, other red blood cell parameters from the CBC are considered, as a normal RDW does not rule out all underlying health conditions.
An elevated RDW, meaning a value above the normal range, indicates that there is a significant variation in the size of your red blood cells. This finding often suggests an issue with red blood cell production or survival. A common cause of high RDW is iron deficiency anemia, where the body produces a mix of smaller and normal-sized red blood cells. Deficiencies in vitamin B12 or folate can also lead to an elevated RDW, often resulting in larger red blood cells.
Beyond nutritional deficiencies, a high RDW can be associated with several other health conditions. These include chronic liver disease, where altered red blood cell maturation can occur. Kidney disease, heart disease, and diabetes are also conditions that may present with an elevated RDW. Additionally, certain types of cancer, such as colorectal cancer, have been linked to increased RDW values.
A low RDW value, which means red blood cells are very uniform in size, is typically not a cause for concern and is not usually associated with specific types of anemia or other health problems. It generally indicates a homogeneous population of red blood cells, which is often seen in healthy individuals. If a low RDW is noted, it is usually evaluated in conjunction with other blood parameters, but it rarely points to a standalone issue.
Why RDW Matters for Health
RDW serves as a useful parameter in assessing a person’s overall health, particularly concerning the body’s red blood cell status. It acts as an early indicator, as an elevated RDW can sometimes precede other noticeable changes in blood parameters, such as hemoglobin levels, in conditions like iron deficiency. This early signal can prompt further investigation into potential underlying issues before they become more pronounced.
The RDW value is not typically used as a standalone diagnostic tool but rather provides valuable clues when interpreted alongside other components of the CBC, especially the Mean Corpuscular Volume (MCV). For instance, a high RDW combined with a low MCV strongly suggests iron deficiency anemia, while a high RDW with a high MCV might indicate a vitamin B12 or folate deficiency. This combined interpretation helps healthcare providers differentiate between various types of anemia, guiding them toward more targeted diagnostic steps.
RDW contributes to a comprehensive health assessment by offering insights into conditions that affect red blood cell production, survival, or overall bone marrow function. Its ability to reflect heterogeneity in red blood cell size can point to nutritional deficiencies, chronic diseases, or other physiological stressors impacting blood cell formation. Consequently, RDW plays a role in guiding further testing and informing treatment strategies for a range of blood disorders and related health concerns.