What is RDW in Blood Work


RDW, or Red Cell Distribution Width, is a part of a standard complete blood count (CBC) test, a common test performed during routine physicals or to diagnose a wide range of disorders. This article will explain what RDW is, its role in diagnosing medical conditions, and what high or low RDW levels might signify.

What is RDW?

RDW is a measure of the variation in size (volume) of your red blood cells (erythrocytes). Red blood cells transport oxygen from your lungs to the rest of your body, and their size can be an important factor in your overall health.

A normal range for RDW for adults is generally considered to be 11.5 to 14.5 percent. However, normal value ranges may slightly vary among different laboratories.

Importance of RDW in Blood Work

The RDW is often used in combination with other CBC results, particularly the mean corpuscular volume (MCV), which is the average volume of a red blood cell. The MCV and RDW can provide insight into potential causes of anemia, a condition in which you lack enough healthy red blood cells to carry adequate oxygen to your body’s tissues.

High RDW Levels

High RDW levels (above the normal range) indicate a larger variation in the size of red blood cells. This could mean that some cells are significantly larger or smaller than the average. Conditions that might cause a high RDW include:

  1. Vitamin B12 or folate deficiency anemia: These types of anemia occur when your body doesn’t have enough of these essential nutrients, leading to the production of unusually large red blood cells.
  2. Iron deficiency anemia: Iron is required for your body to produce hemoglobin, a protein that allows red blood cells to carry oxygen to your tissues. Lack of iron can lead to smaller than average red blood cells, resulting in mixed cell sizes and a high RDW.
  3. Liver disease and alcoholism: Both can affect the production of red blood cells and result in a high RDW.
  4. Hemolytic anemia: This condition causes red blood cells to be destroyed faster than they can be replaced, leading to varied red blood cell sizes.

Low RDW Levels

Low RDW levels (below the normal range) indicate that your red blood cells are more uniform in size. It’s less common to have a low RDW, and it’s usually not a concern unless it accompanies other abnormalities in the CBC.


The RDW in blood work provides valuable information about the size variation of your red blood cells, helping to identify or rule out possible underlying conditions, particularly anemias. However, RDW is typically just one piece of the puzzle. Your healthcare provider will interpret this measurement in conjunction with other tests and clinical findings to reach a diagnosis. If you have concerns about your RDW or other blood work results, it’s crucial to consult with a healthcare professional. This article is intended for informational purposes only and should not replace professional medical advice.

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