RDW puts a number on the spread of red cell sizes around their average. A wider spread means the cells were made under changing conditions over time. Your doctor checks it to help tell apart different causes of anaemia. How even your red cell sizes are gives a useful clue.

What is a normal RDW blood test red cell size variation range?

A typical adult range is around 11.5–14.5%. No India-specific national reference interval is published for this parameter; your lab's printed range is the most reliable comparison. Ranges vary by lab, method and equipment — the range printed on your own report is the one that applies to your result.

RDW — What It Means in Your Blood Test

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This shows how much your red blood cells vary in size from one another.

The RDW result helps you understand whether your red cells look fairly uniform or quite mixed. This gives your doctor an early clue that can narrow down what might lie behind low blood counts.

Also known as: Red Cell Distribution Width, RDW-CV, RDW-SD

Kept in balance

This isn't a case where higher or lower is better. Your body keeps it in a narrow band, and both directions can matter.

Last reviewed: 2026-08-16

What is RDW?

RDW puts a number on the spread of red cell sizes around their average. A wider spread means the cells were made under changing conditions over time.

Why is RDW tested?

Your doctor checks it to help tell apart different causes of anaemia. How even your red cell sizes are gives a useful clue.

What is a normal RDW range?

India: No India-specific national reference interval is published for this parameter; your lab's printed range is the most reliable comparison.
Global: 11.5–14.5%

Ranges vary by lab, method and equipment — the range printed on your own report is the one that applies to your result.

Source: [CLSI, 2010]

What does your RDW value mean?

There is no widely-accepted set of value bands for this parameter. Compare your result with the reference range printed on your own report, and discuss it with your doctor.

What does a high RDW result mean?

A higher-than-usual value means your red cells vary more in size. This can point to mixed nutrient shortages or early anaemia. It is worth discussing with your doctor.

What does a low RDW result mean?

A lower-than-usual value means your red cells are very even in size. This is usually nothing to worry about.

What can affect your RDW result?

Low iron
Vitamin B12 and folate levels
Recent blood transfusion
Thalassemia
Chronic illness

Questions to ask your doctor

About this result

What does my RDW result mean for me specifically, given my age and health?
Is my RDW in the range that is right for me, not just the lab's general range?

What to do next

Could anything I eat, do, or take have affected my RDW result?
Is there anything I should do about my RDW, or is it fine to leave as it is?

About retesting

Does my RDW need to be repeated, and if so, when?
The typical range for RDW can vary between labs — should I compare my result against my own lab's printed range?

The bigger picture

Should my RDW be looked at together with my Hemoglobin and RBC result?
Does my RDW connect to any condition I already have, or to anything I have noticed in how I feel?

Frequently asked questions

What is RDW?: RDW puts a number on the spread of red cell sizes around their average. A wider spread means the cells were made under changing conditions over time. Your doctor checks it to help tell apart different causes of anaemia. How even your red cell sizes are gives a useful clue.
What is a normal RDW blood test red cell size variation range?: A typical adult range is around 11.5–14.5%. No India-specific national reference interval is published for this parameter; your lab's printed range is the most reliable comparison. Ranges vary by lab, method and equipment — the range printed on your own report is the one that applies to your result.
What does a high RDW result mean?: A higher-than-usual value means your red cells vary more in size. This can point to mixed nutrient shortages or early anaemia. It is worth discussing with your doctor.
What does a low RDW result mean?: A lower-than-usual value means your red cells are very even in size. This is usually nothing to worry about.
What can affect your RDW result?: Several everyday factors can influence it, including Low iron, Vitamin B12 and folate levels, Recent blood transfusion, Thalassemia, Chronic illness.

Sources

CLSI (2010) — Clinical and Laboratory Standards Institute EP28-A3c: Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory

Part of the Complete Blood Count (CBC)

See the full Complete Blood Count (CBC) guide

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