Skip to content

Red Blood Cell Distribution Width (RDW) by Volume (RDW-V)

Published: August 9, 2026Updated: August 16, 2026

This test measures the variation in the size of your red blood cells (RBCs). It helps identify conditions affecting RBC production or shape.

Quick summary

["RDW-V assesses red blood cell uniformity, often linked to anemia or other blood disorders."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
34961-3
Short code
Rh Bld Cfm
Synonyms
Rh Bld Cfm
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
confirm
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What Does RDW-V Measure?

RDW-V calculates the standard deviation of RBC volume, reflecting how much the cells differ in size. A higher RDW-V may suggest conditions like iron deficiency anemia, vitamin deficiencies, or bone marrow disorders.

Why Might Your Doctor Order This Test?

Your doctor may order RDW-V to evaluate anemia, monitor treatment responses, or investigate unexplained symptoms like fatigue or weakness. It’s often used alongside other blood tests.

Common Conditions Linked to RDW-V Results

Elevated RDW-V can indicate anemia caused by nutritional deficiencies (e.g., iron, vitamin B12), chronic diseases, or blood disorders. Lower-than-expected RDW-V may rarely suggest conditions like polycythemia or certain genetic disorders.

How Is RDW-V Performed?

This test is typically done as part of a routine blood draw. A small amount of blood is collected, and your healthcare provider will analyze it using automated lab equipment to measure RBC size distribution.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

RDW-V

Frequently asked questions

How often should I expect to get this test?
RDW-V is often included in standard complete blood count (CBC) tests. Your doctor may order it periodically if you have ongoing blood-related symptoms or conditions, or as part of routine check-ups for certain groups (e.g., pregnant women, those with chronic illnesses).
What do my RDW-V results mean if they’re outside the normal range?
Results outside the normal range don’t provide a diagnosis alone. They’re usually reviewed alongside other blood test results and clinical findings. Your doctor will discuss what your specific results mean in the context of your health.
Can lifestyle changes affect RDW-V?
Yes, certain lifestyle factors like diet (e.g., iron-rich foods), smoking, or chronic stress may influence RBC health and potentially RDW-V. Discuss any changes with your doctor if you suspect they’re impacting your blood test results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy