What Does RDW Mean in a Blood Test?

If you've had a CBC blood test, you may have noticed a result called RDW.

But what does RDW mean? Is high RDW a sign of anemia? And what does it mean when your RDW is normal?

Here's a simple explanation.

What Is RDW?

RDW stands for Red Cell Distribution Width.

It describes the variation in the size of your red blood cells.

Your red blood cells are not necessarily all exactly the same size. RDW helps your healthcare professional understand how much their sizes vary.

It is one of the measurements included in a Complete Blood Count (CBC).

What Does a Normal RDW Mean?

A normal RDW generally means there isn't a large variation in red blood-cell size.

However, a normal RDW does not automatically mean your blood results are normal.

RDW needs to be interpreted alongside other CBC measurements, including:

* Hemoglobin

* MCV

* MCH

* MCHC

* RBC count

* Hematocrit

Other tests, such as ferritin, iron studies, vitamin B12 or folate, may also be considered depending on the situation.

What Does High RDW Mean?

A high RDW means there is more variation in red blood-cell size than expected.

This can occur in several situations, including some types of anemia and nutritional deficiencies.

For example, iron deficiency can be associated with an increased RDW, particularly as the condition develops.

Vitamin B12 or folate deficiency can also affect red blood-cell size and distribution.

However, a high RDW by itself does not identify the cause.

What Does Low RDW Mean?

A low RDW generally means your red blood cells are relatively similar in size.

A low RDW is usually less clinically concerning than an elevated RDW, but the result still needs to be interpreted according to the laboratory's reference range and the rest of your blood report.

Why Is RDW Measured With MCV?

RDW and MCV provide different information.

MCV tells you about the average size of your red blood cells.

RDW tells you how much their sizes vary.

Looking at the two together can provide additional information when evaluating anemia.

For example:

Low MCV + high RDW can occur with iron deficiency.

High MCV + high RDW can occur with some vitamin B12 or folate deficiencies.

These are examples rather than diagnoses. Your complete blood results and clinical history need to be considered.

Can RDW Be Normal If You Have Anemia?

Yes.

A normal RDW does not rule out anemia.

This is why it's important not to interpret a single CBC measurement in isolation.

Your hemoglobin, MCV, MCH, ferritin and other relevant results may provide additional information.

When Should You Discuss Your RDW Result?

Consider discussing your CBC with a healthcare professional if you have:

* An abnormal hemoglobin level

* Persistent tiredness or weakness

* Unexplained shortness of breath

* Dizziness or fainting

* Unusual bleeding

* Multiple abnormal CBC results

* Persistently abnormal blood-test results

The significance of an abnormal RDW depends on the overall clinical picture.

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Medical Disclaimer

This article is for educational purposes only and is not a diagnosis or a substitute for professional medical care. RDW results should be interpreted alongside other laboratory results, symptoms and medical history by a qualified healthcare professional.