Red Cell Distribution Width (RDW) is a measurement included in a routine blood test called a complete blood count (CBC). This value helps healthcare providers assess the variation in size and volume of a person’s red blood cells. A high RDW value can indicate an underlying health issue affecting red blood cell production or survival. This article explores the meaning of an elevated RDW and the common conditions that can cause it.
Understanding Red Cell Distribution Width
Red Cell Distribution Width (RDW) is a component of a complete blood count (CBC), a common blood test. RDW measures the variation in the size and volume of your red blood cells, which carry oxygen throughout your body. While healthy red blood cells are generally uniform in size, measuring approximately 6.2 to 8.2 micrometers in diameter, an elevated RDW indicates a wider range of sizes among these cells.
This measurement is expressed as a percentage. A normal RDW typically ranges from 12% to 15%, though values can vary slightly by laboratory. When red blood cells are consistently similar in size, the RDW value will be lower. Conversely, if there is a significant difference in cell sizes, the RDW will be higher.
What an Elevated RDW Indicates
An elevated RDW indicates anisocytosis, a condition where red blood cells are unequal in size. This means that the red blood cells circulating in the bloodstream are not all the same size, with some being smaller and others larger than typical. This variation suggests an issue with the body’s ability to produce or maintain healthy red blood cells. It can point to problems with red blood cell production, their lifespan, or the body’s use of essential nutrients. A high RDW is not a diagnosis on its own, but a valuable indicator for further investigation into a potential underlying medical condition.
Primary Conditions Associated with High RDW
An elevated RDW can stem from several medical conditions that affect red blood cell production or survival.
Nutritional Deficiencies
Nutritional deficiencies are a common cause. Iron deficiency anemia, the most prevalent type, typically results in a high RDW. As iron levels decrease, the body produces smaller red blood cells (microcytes) alongside existing normal-sized cells. This variation can often be detected by an increased RDW even before other indicators of iron deficiency, such as mean corpuscular volume (MCV), fall.
Deficiencies in vitamin B12 and folate also frequently lead to an elevated RDW. These deficiencies impair DNA synthesis, which is necessary for proper red blood cell maturation, resulting in abnormally large red blood cells (macrocytes). If both iron and vitamin B12 or folate deficiencies are present, the RDW can be particularly high due to the presence of both smaller and larger cells.
Chronic Diseases
Chronic diseases can also contribute to an elevated RDW. Anemia of chronic disease, often seen in conditions like kidney disease, inflammatory conditions, or cancer, can lead to a high RDW. While red blood cells in anemia of chronic disease may often be relatively uniform in size, chronic inflammation and oxidative stress can still cause variations in red blood cell size.
Inherited Blood Disorders
Inherited blood disorders are another category. Thalassemia, a genetic disorder affecting hemoglobin production, can cause red blood cells to be smaller than average and vary in size. While some forms of thalassemia may present with a normal RDW, others can show an elevated RDW due to the heterogeneity of red blood cell sizes. Sickle cell anemia, characterized by abnormally shaped red blood cells, also typically results in an elevated RDW.
Myelodysplastic Syndromes (MDS)
Myelodysplastic syndromes (MDS), a group of bone marrow disorders, are linked to elevated RDW. These conditions involve ineffective production of blood cells in the bone marrow, leading to red blood cells of various sizes and shapes. The increased RDW in MDS reflects this dyserythropoiesis, or abnormal red blood cell development.
Other Factors
Other factors can influence RDW levels. Liver disease can lead to an elevated RDW due to impaired red blood cell production and increased red blood cell destruction. The liver plays a role in iron metabolism and red blood cell maturation, and its dysfunction can disrupt these processes. Additionally, recent blood transfusions can temporarily increase RDW as donor red blood cells mix with the recipient’s existing cells. This effect is generally more pronounced if there is a significant difference between the mean corpuscular volume of the donor’s and recipient’s red blood cells.
Interpreting Results and Next Steps
An elevated RDW is an important piece of information that helps guide further diagnostic steps. It is rarely interpreted in isolation; instead, healthcare providers evaluate the RDW in conjunction with other parameters from a complete blood count, particularly the mean corpuscular volume (MCV), which measures the average size of red blood cells. This combined assessment helps differentiate between various types of anemia and other underlying conditions.
For example, a high RDW coupled with a low MCV often suggests iron deficiency anemia, while a high RDW with a high MCV may point towards vitamin B12 or folate deficiencies. A doctor will also consider a patient’s symptoms, medical history, and other relevant clinical findings when interpreting these blood test results. Further diagnostic tests, such as iron studies, vitamin B12 and folate levels, or even a bone marrow biopsy in some cases, may be ordered to pinpoint the exact cause of the elevated RDW. It is important to consult a healthcare professional for an accurate diagnosis and appropriate treatment plan, as self-diagnosis based solely on RDW values is not advisable.