The Red Cell Distribution Width, or RDW, is a measurement routinely included in a complete blood count (CBC) test. This parameter offers insights into the health of your red blood cells, which are responsible for carrying oxygen throughout your body. By examining variations in these cells, RDW can provide initial clues about certain underlying health conditions.
Understanding RDW
RDW stands for Red Cell Distribution Width. It quantifies the variation in the size and volume of red blood cells in a blood sample. Normally, red blood cells are relatively uniform in size. A higher RDW value indicates greater variability in red blood cell size, a condition known as anisocytosis. Conversely, a lower RDW suggests that red blood cells are more similar in size.
What RDW Results Indicate
The reference range for RDW is typically between 11.5% and 15.4%, though slight variations can occur between laboratories. A result within this range signifies that your red blood cells are largely consistent in size. However, a normal RDW does not always rule out an underlying health issue, as some conditions may present with a normal RDW despite other red blood cell abnormalities.
A high RDW, exceeding the normal range, indicates a significant variation in red blood cell size. This suggests that new red blood cells being produced are different in size from older, circulating cells. An elevated RDW can be an early indicator of certain problems, sometimes even before other red blood cell parameters, like mean corpuscular volume (MCV) or hemoglobin levels, show changes. In contrast, a low RDW, meaning less variability in cell size, is generally not considered a clinical concern and is a much less common finding than a high RDW.
Common Conditions Associated with Abnormal RDW
An abnormal RDW, particularly an elevated one, can be observed in various medical conditions. Different types of anemia are frequently associated with a high RDW. For instance, in iron deficiency anemia, the body produces smaller, iron-deficient red blood cells alongside existing normal-sized cells, leading to a mixed population and an increased RDW.
Similarly, deficiencies in vitamin B12 or folate can result in larger-than-normal red blood cells, known as macrocytic anemia, which also contributes to a higher RDW due to the presence of both large and normal cells. In cases of mixed deficiencies, such as both iron and vitamin B12 deficiency, the RDW can be notably elevated as there is a combination of both small and large red blood cells. Conditions like sickle cell anemia, where red blood cells have an abnormal, crescent shape, and certain types of thalassemia, inherited blood disorders affecting hemoglobin production, can also lead to an elevated RDW due to variations in cell size and shape.
Beyond anemias, a high RDW can also be linked to other health issues. Chronic inflammation, liver disease, and myelodysplastic syndromes, a group of disorders where the bone marrow does not produce enough healthy blood cells, can all impact red blood cell production and result in an elevated RDW. RDW is a supplementary diagnostic tool and is interpreted in conjunction with other CBC parameters, like MCV and hemoglobin levels, and the patient’s overall clinical presentation for an accurate diagnosis.