A routine blood test, specifically a complete blood count (CBC), includes the Red Cell Distribution Width (RDW). This parameter focuses on red blood cells, which carry oxygen throughout the body. The RDW value assesses the uniformity of these cells, indicating red blood cell health.
Understanding Red Cell Distribution Width
Red Cell Distribution Width (RDW) quantifies the variation in the size and volume of red blood cells within a blood sample. This measurement is distinct from the mean corpuscular volume (MCV), which indicates the average size of red blood cells. The RDW test detects anisocytosis, a condition where red blood cells are of unequal sizes, serving as a numerical representation of this variability. The RDW is reported as a percentage and is a standard component of a complete blood count. For most adults, a normal RDW range is between 11.5% and 14.5%, with values outside this range indicating more or less variation than expected.
Interpreting an Elevated RDW
An elevated RDW signifies a greater variation in the size of red blood cells circulating in the bloodstream than normal. This means the blood sample contains a mix of red blood cells that are significantly smaller or larger than average, or both. This variation often suggests the body is producing red blood cells that differ in size from the existing population. While a high RDW points to a disparity in red blood cell size, it is not a diagnosis in itself. Instead, it functions as a signal, prompting healthcare professionals to investigate further to determine the underlying cause.
Conditions Associated with High RDW
Several medical conditions can lead to an elevated Red Cell Distribution Width, as they disrupt the normal production or lifespan of red blood cells. Iron-deficiency anemia is a common cause, where a lack of iron results in the production of smaller, paler red blood cells (microcytic cells), alongside existing normal-sized cells. This mixture of cell sizes directly contributes to an increased RDW. Similarly, deficiencies in vitamin B12 or folate can cause macrocytic anemia, leading to the production of unusually large, immature red blood cells.
Chronic diseases, such as kidney disease or liver disease, can also impact red blood cell production and lead to an elevated RDW. Kidney disease can reduce the production of erythropoietin, a hormone essential for red blood cell formation, causing varied cell sizes. Inflammatory conditions, like chronic infections or autoimmune disorders, may also influence bone marrow function and red blood cell maturation, resulting in RDW elevation. Recent significant blood loss, which stimulates the rapid production of new, often immature and varied-sized cells, can also cause a temporary increase in RDW.
Myelodysplastic syndromes, disorders where the bone marrow fails to produce healthy blood cells, frequently manifest with an elevated RDW. Certain nutritional deficiencies beyond iron or B vitamins, or even a combination of deficiencies, can contribute to anisocytosis and a high RDW.
What to Do After a High RDW Result
Receiving a high RDW result in a blood test should prompt a consultation with a healthcare professional. This elevated value is an indicator, not a definitive diagnosis, and requires further medical evaluation to identify the specific cause. Your doctor will consider the RDW in conjunction with other parameters from your complete blood count, such as mean corpuscular volume (MCV), hemoglobin levels, and red blood cell count.
For instance, a high RDW coupled with a low MCV might suggest iron deficiency anemia, while a high RDW with a high MCV could point towards vitamin B12 or folate deficiency. Your doctor will also take into account your symptoms, medical history, and any other relevant health factors.
To pinpoint the underlying cause, your healthcare provider may order additional diagnostic tests. These could include specific iron studies, vitamin B12 and folate levels, or tests to assess kidney and liver function. In rarer cases, if more serious conditions like myelodysplastic syndromes are suspected, a bone marrow biopsy might be recommended. Early consultation ensures timely investigation and management of any identified health condition.