A routine blood test provides a wealth of information about your overall health. One of the measurements included in a standard Complete Blood Count (CBC) is the Red Cell Distribution Width (RDW). This test assesses the physical characteristics of your red blood cells, which are responsible for transporting oxygen from your lungs to the rest of your body. The RDW value specifically provides information about the variation in the size and volume of these cells.
Understanding the RDW Blood Test
The RDW test measures the degree of variation in the size and shape of your red blood cells, a condition known as anisocytosis. In a healthy individual, red blood cells are uniform in size. A low RDW value indicates your red blood cells are similar in size, which is normal. A high RDW value signifies a considerable difference between the size of your smallest and largest red blood cells.
Think of it like a collection of stones; a low RDW is like a bag of nearly identical marbles, while a high RDW is like a bag of assorted pebbles. This variability can be an early indicator of certain health issues. While reference ranges can vary slightly between laboratories, a normal RDW is between 12.2% and 16.1% for adult females and 11.8% to 14.5% for adult males.
The Connection Between High RDW and Cancer
Research has identified an association between an elevated RDW and an increased risk for certain types of cancer, including colorectal, lung, breast, and various blood-related malignancies. A high RDW is a non-specific marker, not a direct diagnostic tool for cancer. It signals that an underlying process is affecting red blood cell production or survival, which prompts further investigation.
Several biological mechanisms may explain this connection. Chronic inflammation, a common feature of many cancers, can disrupt red blood cell production in the bone marrow, leading to the release of differently sized cells. This process, known as ineffective erythropoiesis, means the bone marrow is failing to produce healthy, uniform red blood cells.
Cancer can place significant demands on the body, leading to nutritional deficiencies that impact red blood cell development. For example, issues with iron absorption or metabolism can affect the size and quality of red blood cells. The cancer or its treatments can also directly suppress bone marrow function, contributing to variations in cell size and a higher RDW.
Other Medical Conditions That Cause High RDW
An elevated RDW is not exclusively linked to cancer and can be caused by a variety of other, often more common, medical conditions. A wide range of issues can affect the uniformity of red blood cells, leading to a high RDW reading.
Nutrient deficiencies are a frequent cause. A lack of iron, vitamin B12, or folate can lead to different types of anemia, all characterized by abnormal red blood cell production and a higher RDW. For example, with iron-deficiency anemia, the body cannot produce enough healthy red blood cells without adequate iron.
Chronic diseases can also result in a high RDW. Conditions like chronic kidney or liver disease disrupt the body’s ability to regulate red blood cell production. Chronic inflammation from autoimmune disorders can interfere with bone marrow function. A recent blood transfusion can also temporarily increase the RDW, as the transfused cells will have a different size profile from the recipient’s own.
Interpreting RDW Results and Next Steps
A single lab value is never interpreted in isolation. A healthcare provider analyzes the RDW result in the context of the entire CBC panel, which includes hemoglobin, hematocrit, and Mean Corpuscular Volume (MCV). This comprehensive view, combined with your personal health history and symptoms, allows for a more accurate interpretation.
An elevated RDW signals that further investigation may be necessary, acting as a starting point rather than a conclusion. Your doctor will look at other blood cell indices to narrow down potential causes. For example, a high RDW combined with a low MCV (smaller average cell size) might point towards iron-deficiency anemia. In contrast, a high RDW with a high MCV (larger average cell size) could suggest a vitamin B12 or folate deficiency.
Discuss your results with your healthcare provider. They can determine if additional testing is needed to identify the underlying cause of the abnormal RDW. This may include specific nutrient level checks, liver function tests, or imaging studies to ensure the result is properly contextualized and that any necessary follow-up actions are taken.