Red Cell Distribution Width – Coefficient of Variation, or RDW-CV, is a metric reported as part of a routine complete blood count (CBC) test. This blood test provides a comprehensive overview of various components in your blood, including red blood cells. RDW-CV specifically focuses on a particular characteristic of these oxygen-carrying red blood cells. It offers insights into their uniformity, which can be an indicator of overall red blood cell health.
What RDW-CV Measures
RDW-CV quantifies the variation in the size of your red blood cells. Normally, red blood cells maintain a relatively uniform size, but certain conditions can cause them to differ significantly in volume. This variation in red blood cell size is medically termed anisocytosis. A higher RDW value indicates a greater degree of size variation among these cells.
This measurement differs from Mean Corpuscular Volume (MCV), which indicates the average size of red blood cells. While MCV provides an average, RDW-CV reveals the range of sizes present in the blood sample, offering a more complete picture of red blood cell heterogeneity. The RDW-CV is influenced by the average red blood cell size (MCV).
Why RDW-CV is Tested
The RDW-CV test is a component of the complete blood count (CBC), a common diagnostic tool. It serves a valuable purpose in helping healthcare providers assess red blood cell health beyond just their average size or number. The test helps in differentiating between various types of anemia and other blood disorders. For instance, it can aid in distinguishing anemias that might present with similar symptoms but have different underlying causes.
RDW-CV is particularly useful when evaluated alongside other red blood cell indices like MCV and hemoglobin levels. Its elevation can sometimes precede changes in other red cell parameters, potentially offering an early diagnostic clue for certain conditions. The RDW-CV provides a more detailed understanding of red blood cell dynamics, assisting in a more precise diagnosis and treatment plan.
Interpreting Your RDW-CV Results
Normal RDW-CV ranges typically fall between 11.5% and 14.5%, though these values can vary slightly depending on the laboratory. A result within this range generally suggests that your red blood cells are relatively uniform in size. It is important to note that a normal RDW-CV does not automatically rule out all medical conditions, as other factors and tests are considered.
A high RDW-CV indicates a greater variation in red blood cell size, a condition known as anisocytosis. This can occur when the body produces new red blood cells that are different in size from existing ones. Elevated RDW-CV values are frequently associated with various types of anemia, such as iron deficiency anemia, where new, smaller cells might be produced alongside older, normal-sized cells. High RDW-CV can also be a sign of deficiencies in vitamin B12 or folate, which can lead to the production of abnormally large red blood cells. Other conditions linked to a high RDW-CV include chronic diseases, recent blood loss, or disorders affecting the bone marrow.
A low RDW-CV, where red blood cells are very similar in size, is uncommon and typically not considered clinically significant. It rarely points to a medical problem on its own. When interpreting RDW-CV results, healthcare providers consider them in the context of other blood test parameters and a patient’s overall health history.
Common Factors Influencing RDW-CV
Several factors can lead to an elevated RDW-CV, reflecting a diverse population of red blood cell sizes. Nutritional deficiencies are a common cause, as inadequate levels of essential nutrients can disrupt normal red blood cell production. For example, a lack of iron can lead to the production of smaller red blood cells, while deficiencies in vitamin B12 or folate can result in larger, often irregularly shaped cells. When these new, differently sized cells mix with existing ones, the RDW-CV increases.
Chronic diseases also frequently impact RDW-CV levels. Conditions such as kidney disease, liver disease, certain inflammatory disorders, and even some cancers can affect the body’s ability to produce healthy, uniformly sized red blood cells. These diseases can interfere with red blood cell development or survival, leading to a wider range of cell sizes. For instance, chronic kidney disease can impair erythropoietin production, a hormone essential for red blood cell formation.
Acute or chronic blood loss, as well as conditions causing the premature destruction of red blood cells (hemolysis), can also elevate RDW-CV. In response to blood loss or increased destruction, the bone marrow ramps up red blood cell production, releasing new cells that may differ in size from older, remaining cells, thereby increasing the variability. Additionally, recent blood transfusions can temporarily increase RDW-CV as the body integrates donor cells, which may vary in size from the recipient’s own red blood cells.