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Erythrocyte Distribution Width (RDW) by Electrophoresis

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

This test measures the variation in size of your red blood cells (RBCs). It helps assess whether your RBCs are uniformly sized or if some are unusually large or small.

Quick summary

["RDW can signal potential blood disorders or nutritional deficiencies."]

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

Key facts at a glance

LOINC
41858-2
Short code
EDDP Ur Ql
Synonyms
EDDP Ur Ql
Category
chemistry
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why RDW Matters in Blood Health

RDW is a simple blood test that checks how evenly sized your red blood cells are. Normally, RBCs are similar in size, but if they vary widely, it may indicate underlying health issues like anemia, iron deficiency, or other blood disorders.

When Your Doctor Might Order This Test

Your doctor may request an RDW test if you have symptoms like fatigue, pale skin, shortness of breath, or if they suspect conditions like anemia, vitamin deficiencies (such as B12 or folate), or other blood-related problems.

How the Test Works

A small blood sample is taken, and your red blood cells are analyzed using electrophoresis. This method separates cells by size, allowing the lab to measure the spread (variation) in their sizes.

What the Results Mean

Higher-than-normal RDW levels may suggest conditions like anemia or nutritional deficiencies. Lower-than-normal levels are less common but could indicate certain blood disorders. Your results will be compared to a general reference range provided by your lab.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

RDW (Serum Electrophoresis)

Frequently asked questions

RDW is often used alongside other blood tests to help diagnose and monitor conditions like anemia, particularly microcytic (small RBCs) or macrocytic (large RBCs) types. It can also guide treatment decisions for conditions like pernicious anemia or vitamin deficiencies.
An RDW test alone doesn’t diagnose a specific condition, but it helps your healthcare provider assess overall red blood cell health and guide further testing if needed.
What causes RDW to be elevated?
Elevated RDW levels can result from conditions like iron deficiency anemia, vitamin B12 or folate deficiency, chronic diseases, or certain types of anemia. It may also appear in cases of liver disease or after certain blood transfusions.
Can RDW levels change over time?
Yes, RDW levels can fluctuate depending on your overall health, diet, and treatment for conditions like anemia. Regular monitoring may be needed if you have ongoing symptoms or conditions that affect RBC production.
  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