what is rdw blood work

3 min read 12-03-2025

Red blood cell distribution width (RDW) is a blood test that measures the variation in the size of your red blood cells. Understanding your RDW results can provide valuable insights into your overall health and help diagnose various medical conditions. This article will delve into what RDW is, how it's measured, what the results mean, and what conditions it can help identify.

What is RDW and Why is it Important?

Red blood cells, or erythrocytes, carry oxygen throughout your body. They are typically uniform in size and shape. However, diseases and other factors can cause variations in their size, a condition known as anisocytosis. RDW quantifies this variation. A higher RDW indicates greater variability in red blood cell size, suggesting potential underlying health issues. Conversely, a normal RDW usually suggests healthy red blood cell production.

How is RDW Measured?

The RDW test is typically performed as part of a complete blood count (CBC). It's a simple, non-invasive blood test that requires a small blood sample drawn from a vein in your arm. The blood sample is then analyzed by a specialized machine that measures the size and distribution of your red blood cells. The result is expressed as a percentage or coefficient of variation (CV).

Understanding Your RDW Results

RDW results are usually interpreted in conjunction with other blood test results, such as hemoglobin levels, hematocrit, and mean corpuscular volume (MCV). The normal range for RDW can vary slightly depending on the laboratory, but generally falls between 11.5% and 14.5%.

High RDW (Increased RDW): Possible Causes and Implications

A high RDW indicates that your red blood cells are more varied in size. This can be a sign of several conditions, including:

Iron deficiency anemia: This is a common cause of a high RDW. Lack of iron impairs the body's ability to produce healthy red blood cells, resulting in smaller, varied cells.
Vitamin B12 deficiency anemia: Similar to iron deficiency, a lack of vitamin B12 also affects red blood cell production, leading to size variations.
Folate deficiency anemia: Folate is crucial for red blood cell development. Deficiency leads to abnormal red blood cell production and a high RDW.
Thalassemia: This is a genetic disorder affecting hemoglobin production, often resulting in smaller red blood cells and a high RDW.
Myelodysplastic syndromes (MDS): These are a group of bone marrow disorders that can lead to abnormal blood cell production, including red blood cells with varying sizes.
Chronic diseases: Conditions like kidney disease, liver disease, and certain cancers can also cause a high RDW.
Recent blood loss: Significant blood loss can lead to an increase in RDW as the body tries to replenish its red blood cell supply.

Note: A high RDW alone is not a definitive diagnosis. Further testing and clinical evaluation are necessary to determine the underlying cause.

Low RDW (Decreased RDW): Possible Causes and Implications

While less common than a high RDW, a low value might indicate:

Iron overload: An excess of iron can result in uniformly sized, but abnormally large red blood cells.
Certain types of anemia: Some rare forms of anemia may present with a low RDW.

A low RDW is usually less concerning than a high RDW. However, it's still crucial to discuss any abnormalities with your doctor.

What to Expect During and After an RDW Test

The RDW blood test itself is simple and painless. After the blood draw, there’s minimal discomfort. Your doctor will review your results along with other relevant tests to determine the appropriate course of action, which might include further testing or treatment for underlying conditions.

Frequently Asked Questions (FAQs)

Q: Is a high RDW always a serious problem?

A: Not necessarily. While a high RDW often indicates an underlying condition, it’s not always indicative of a serious illness. Further tests are needed for proper diagnosis and treatment.

Q: Can I get an RDW test on its own?

A: An RDW test is usually part of a complete blood count (CBC). It's rarely ordered in isolation.

Q: How long does it take to get the results of an RDW test?

A: Results are typically available within a day or two.

This information is for educational purposes only and should not be considered medical advice. Always consult with a healthcare professional for any health concerns or before making any decisions related to your health or treatment. They can interpret your RDW results in context with your complete medical history and other test results.