Red Cell Distribution Width, or RDW, is a measurement included in a common blood test called a complete blood count (CBC). It provides insight into the variation in size and volume of your red blood cells. While it might sound technical, understanding RDW can offer valuable information about your overall health.
What RDW Measures
Red Cell Distribution Width (RDW) measures the variation in the size and volume of your red blood cells (RBCs). Red blood cells transport oxygen from your lungs to tissues throughout your body. Healthy red blood cells typically maintain a uniform size. The RDW value indicates how much these cells differ from each other in size, rather than just their average size. A high RDW means there’s a greater range of sizes among your red blood cells, a condition known as anisocytosis.
Why RDW is Important
The RDW test is a component of a complete blood count (CBC), a routine blood test that assesses various blood components. This measurement helps identify different health conditions, particularly various types of anemia. It offers clues about red blood cell production and their overall health. RDW can also help differentiate between conditions with similar symptoms, aiding in a more precise diagnosis. An elevated RDW can sometimes indicate an issue before other red blood cell measurements change.
Understanding Your RDW Results
The typical healthy range for RDW in adults generally falls between 11.5% and 14.5%. Reference ranges can differ based on population, sex, and the hematology analyzer used.
A high RDW indicates a greater variation in the size of your red blood cells. This can be a sign of several conditions, including nutrient deficiencies such as iron, folate, or vitamin B12 deficiency. Iron deficiency anemia often shows a high RDW because the body produces red blood cells of different sizes as it tries to compensate for the lack of iron. A high RDW can also be associated with macrocytic anemia, where red blood cells are larger than normal, often due to folate or vitamin B12 deficiencies. Other conditions linked to high RDW include chronic inflammation, certain liver diseases, kidney disease, and myelodysplastic syndrome.
A low RDW is less common and suggests that your red blood cells are uniform in size. This result is usually not considered clinically significant on its own and is often a favorable finding. It can suggest stable red blood cell production. It may be observed in conditions like thalassemia minor or anemia of chronic disease, where red blood cells are consistently sized despite being smaller.
Next Steps After an Abnormal RDW
An abnormal RDW result alone does not provide a definitive diagnosis. It is a single piece of information that healthcare professionals use in conjunction with other blood test results, such as mean corpuscular volume (MCV) and hemoglobin levels, to get a complete picture of your health. Your doctor will interpret your RDW in the context of your overall health, symptoms, and medical history. Further diagnostic tests or adjustments to your lifestyle or treatment plan may be recommended based on a comprehensive evaluation.