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What is Red Cell Distribution Width (RDW) in Blood Test: What is High and Low RDW Value? Causes & Treatment?

Updated: Jun 19, 2024

  • Red cell distribution width (RDW) is a test to measure differences in the size of red blood cells (erythrocytes) in the blood.

  • Red blood cells (RBC) are blood cells that carry oxygen from the lungs to tissues and organs.

  • Normally, healthy red blood cells should be approximately 6.2 to 8.2 micrometers in size. A high RDW means there is a large difference between the sizes of your smallest and largest red blood cells. This could be a sign of a medical condition such as anemia or thalassemia.

  • In a blood test, MCV and RDW are parameters related to the size of red blood cells.

Red cell distribution width (RDW) is a test to measure differences in the size of red blood cells (erythrocytes) in the blood.  Red blood cells (RBC) are blood cells that carry oxygen from the lungs to tissues and organs.   Normally, healthy red blood cells should be approximately 6.2 to 8.2 micrometers in size. A high RDW means there is a large difference between the sizes of your smallest and largest red blood cells. This could be a sign of a medical condition such as anemia or thalassemia.   In a blood test, MCV and RDW are parameters related to the size of red blood cells. Normal RDW values according to these measurement methods are RDW-SD: 39-46 fL RDW-CV: 11.5-14.5% in adults.  Normally, healthy red blood cells should be approximately 6.2 to 8.2 micrometers in size. A high RDW means there is a large difference between the sizes of your smallest and largest red blood cells. This appears in the test report as a value above the reference value (14.5%). Low RDW indicates that red blood cells are below the required size. This appears as a value below the lower reference value (11.5%)  in the test report.   Low RDW is not as common as high RDW. Low RDW can also provide important insights into your health.
What is Red Cell Distribution Width (RDW) in Blood Test: What is High and Low RDW Value? Causes & Treatment?

What is A Normal RDW Range in Blood Test ?

  • There are two ways to measure RDW: RDW-CV (RDW coefficient of variation) and RDW-SD (RDW standard deviation).

  • Normal RDW values according to these measurement methods are RDW-SD: 39-46 fL RDW-CV: 11.5-14.5% in adults. The range may slightly vary between laboratories.

  • A normal RDW value does not always mean that there is no problem. It is important to remember that some types of anemia and diseases can be observed with a normal RDW result.


What is High RDW Value in Blood Test?

  • Normally, healthy red blood cells should be approximately 6.2 to 8.2 micrometers in size. A high RDW means there is a large difference between the sizes of your smallest and largest red blood cells. This appears in the test report as a value above the reference value (14.5%).

  • High RDW may be an indicator of some diseases.


What Causes High RDW Level in Blood Test?

A high RDW result can be a sign of other conditions, such as:

  • Iron deficiency

  • Different types of anemia

  • Thalassemia

  • Sickle cell anemia

  • Chronic liver disease

  • Heart disease

  • Diabetes

  • Kidney disease

  • Cancer


High RDW Symptoms

High RDW itself does not typically cause symptoms. The symptoms experienced are often related to the underlying condition or disease. If anemia is present, weakness, dizziness, pale skin, and cold hands and feet are common symptoms.


How to Treat High RDW Level?

High RDW treatment is tailored to the underlying cause. Your doctor will organize the appropriate treatment according to the diagnosis. Besides, what can be done?

  • Follow a balanced diet

A nutritious and balanced diet helps reduce the effects of iron, folate and B-12 deficiency that cause high RDW values.

  • Quit smoking

Quitting smoking has many health benefits and is also known to be effective in reducing the RDW value.

  • Stay away from alcohol

Heavy alcohol consumption reduces the absorption of vitamin B12 and folate. This causes the RDW to rise. Alcohol should be avoided to reduce the RDW value to required levels.

  • Pay attention to sleep patterns

Studies have shown that the RDW values of people who sleep regularly and balancedly reach the desired level.

  • Regular exercise

Regular exercise should become an indispensable part of life. Regular exercise and walking are recommended to lower the RDW value.


What is Low RDW Value in Blood Test?

  • Low RDW indicates that red blood cells are below the required size. This appears as a value below the lower reference value (11.5%) in the test report.

  • Low RDW is not as common as high RDW. Low RDW can also provide important insights into your health.


What Causes Low RDW Level in Blood Test?

  • Vitamin B6 deficiency

  • Chronic anemia

  • Iron deficiency anemia

  • Arthritis

  • Thalassemia

  • High blood loss

  • Hemoglobin E disease


Low RDW Symptoms

  • Diarrhea

  • Heart palpitations

  • Tiredness

  • Nausea may occur.


How to Treat Low RDW Level?

To treat low RDW, the underlying cause must be identified. Treatment will be directed towards this disease. Treatment can be supported by paying attention to diet and lifestyle.

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