RDW-CV (Red Cell Distribution Width) in %

Blood

Other names: RBC Distribution Width, RED DISTRIB. WIDTH, RBC Distrib Width

check icon Optimal Result: 11.7 - 15.4 %.

Reviewed by HealthMatters Editorial Team · Last updated February 2026


What does RDW-CV mean on a blood test?

RDW-CV (Red Cell Distribution Width – Coefficient of Variation) measures how much your red blood cells vary in size, expressed as a percentage.

It is part of a routine Complete Blood Count (CBC).

  • A higher RDW-CV means greater variation in red blood cell size.

  • A lower RDW-CV means red blood cells are more uniform in size.

RDW-CV does not diagnose a condition on its own. It is interpreted together with:

  • Hemoglobin

  • MCV (Mean Corpuscular Volume)

  • Iron studies

  • Vitamin B12

  • Folate


RDW-CV normal range

Typical reference range:

11.5% – 14.5%

(Some labs use 11.7% – 15.4%)

Ranges vary slightly by laboratory. Mild elevations are common and not always clinically significant.

RDW-CV becomes meaningful when interpreted alongside other CBC markers.


What is the difference between RDW-CV and RDW-SD?

Some labs report two forms of RDW:

RDW-CV (%)

  • Expressed as a percentage

  • Reflects size variation relative to average cell size

  • Influenced by MCV

RDW-SD (fL)

  • Measured in femtoliters

  • Reflects the actual width of the red cell size distribution curve

  • Not directly influenced by MCV

RDW-CV is more commonly reported.
RDW-SD may provide additional detail in complex anemia patterns.

If both are available, doctors interpret them together with MCV.


What does high RDW-CV mean?

A high RDW-CV indicates anisocytosis, meaning red blood cells vary significantly in size.

Common causes of elevated RDW-CV

  • Iron deficiency

  • Vitamin B12 deficiency

  • Folate deficiency

  • Mixed nutrient deficiencies

  • Recent blood loss

  • Chronic inflammation

  • Chronic disease

  • Liver disease

  • Recovery phase after anemia treatment

RDW often rises early in anemia, sometimes before hemoglobin drops.


High RDW-CV but normal hemoglobin

A mildly elevated RDW-CV with normal hemoglobin is common.

Possible explanations:

  • Early iron deficiency

  • Early B12 or folate deficiency

  • Recovery from illness

  • Mild inflammation

  • Recent blood donation

Doctors often monitor this pattern over time before initiating treatment.


What does low RDW-CV mean?

Low RDW-CV means red blood cells are very uniform in size.

In most cases, low RDW-CV is not clinically significant.

It may appear when:

  • Red blood cells are consistently small

  • Red blood cells are consistently large

  • Bone marrow production is stable

  • Other CBC markers are normal

Low RDW-CV alone rarely indicates disease.


RDW-CV and MCV patterns

Doctors frequently interpret RDW-CV together with MCV.

High RDW + Low MCV

Often suggests iron deficiency anemia.

High RDW + High MCV

May suggest vitamin B12 or folate deficiency.

High RDW + Normal MCV

May indicate early anemia, mixed deficiencies, or chronic disease.

This combination approach helps narrow down the underlying cause.


What level of RDW-CV is dangerous?

There is no single “dangerous” RDW-CV value by itself.

Concern increases when high RDW-CV appears with:

  • Low hemoglobin

  • Abnormal MCV

  • Low iron levels

  • Persistent symptoms

  • Evidence of chronic disease

RDW is always interpreted in context.


Symptoms associated with abnormal RDW

RDW itself does not cause symptoms.
Symptoms come from the underlying condition, such as anemia.

Possible symptoms include:

  • Fatigue

  • Weakness

  • Dizziness

  • Pale skin

  • Shortness of breath

  • Cold hands and feet

If you have symptoms along with abnormal RDW, follow up with your provider.


Can RDW-CV be lowered?

RDW improves when the underlying cause is addressed.

Treatment depends on the reason for elevation and may include:

  • Iron supplementation

  • Vitamin B12 replacement

  • Folate supplementation

  • Treating chronic inflammation

  • Managing underlying disease

Balanced nutrition and adequate intake of iron, B12, and folate support healthy red blood cell production.


Key Takeaway

RDW-CV measures variation in red blood cell size.

  • High RDW-CV often reflects nutrient deficiency or anemia.

  • Low RDW-CV is usually not concerning.

  • Interpretation requires hemoglobin, MCV, and iron markers.

RDW-CV is a useful early signal — but it must be interpreted in context.

What does it mean if your RDW-CV (Red Cell Distribution Width) in % result is too high?

A high RDW means there is greater variation in the size of your red blood cells.
This is called anisocytosis.

High RDW is most commonly associated with anemia or nutrient deficiencies, but it does not diagnose a condition on its own.


Common causes of high RDW

High RDW may occur with:

  • Iron deficiency

  • Vitamin B12 deficiency

  • Folate deficiency

  • Recent blood loss

  • Chronic disease

  • Liver disease

  • Inflammation

  • Bone marrow stress

RDW often increases early in anemia — sometimes before hemoglobin drops.


High RDW and MCV patterns

Doctors interpret RDW together with MCV:

High RDW + Low MCV
Often suggests iron deficiency anemia.

High RDW + High MCV
May suggest B12 or folate deficiency.

High RDW + Normal MCV
May indicate early or mixed anemia.


Symptoms related to high RDW

RDW itself does not cause symptoms.
Symptoms come from underlying anemia and may include:

  • Fatigue

  • Weakness

  • Shortness of breath

  • Dizziness

  • Pale skin

  • Cold hands and feet


Is high RDW dangerous?

High RDW is not dangerous by itself.
It becomes more clinically important when combined with:

  • Low hemoglobin

  • Abnormal MCV

  • Iron deficiency

  • Ongoing symptoms

Your provider may order iron studies, B12, or folate testing to determine the cause.


Can RDW be lowered?

RDW improves when the underlying cause is treated.

Depending on the cause, treatment may include:

  • Iron supplementation

  • Vitamin B12 or folate replacement

  • Treating chronic disease

  • Addressing inflammation

Lifestyle factors like balanced nutrition and avoiding excessive alcohol can support healthy red blood cell production, but treatment depends on the root cause.

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What does it mean if your RDW-CV (Red Cell Distribution Width) in % result is too low?

A low RDW means your red blood cells are very similar in size.
In most cases, this is normal and not a cause for concern.

RDW measures variation in red blood cell size. When that variation is small, the RDW value is lower.


Is low RDW dangerous?

Usually, no.

Low RDW is generally considered clinically insignificant — especially if:

  • Hemoglobin is normal

  • MCV is normal

  • You have no symptoms

Doctors rarely treat low RDW on its own.


When can low RDW appear?

Low RDW may be seen when:

  • Red blood cells are uniformly small (microcytic pattern)

  • Red blood cells are uniformly large (macrocytic pattern)

  • Bone marrow production is stable

  • Other CBC markers are normal

In some anemia patterns, RDW can be low because all red blood cells are consistently the same size.


When to speak with a doctor

You should discuss results with your provider if low RDW appears with:

  • Low hemoglobin

  • Fatigue

  • Shortness of breath

  • Abnormal MCV

Otherwise, low RDW alone is rarely concerning.


Key takeaway

Low RDW usually reflects uniform red blood cell size and is typically not a health problem. It is interpreted alongside other CBC markers.

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