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Guided Red Blood Cell Distribution Width (RDW) Analysis

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

This test measures the variation in size of your red blood cells (RBCs) to help assess potential blood disorders, anemia, or nutritional deficiencies.

Quick summary

["Red blood cell size differences may signal underlying health concerns needing further evaluation."]

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

Key facts at a glance

LOINC
82126-4
Short code
PT Guided RT
Synonyms
PT Guided RT
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0.8
Ref high
1.2
Critical range
— – 5 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
pt
CPT
85610
SNOMED
396252006
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms like fatigue, pale skin, or unusual bleeding. It can also be part of routine blood checks or when investigating conditions like iron deficiency or vitamin B12 deficiency.

What to Expect Before the Test

No special preparation is needed. A simple blood draw from a vein in your arm is all that’s required. The process takes a few minutes, and you may feel slight discomfort.

What the Results Mean

A wider range of RBC sizes (higher RDW) may indicate conditions like anemia, chronic illness, or nutritional deficiencies. A narrower range suggests normal RBC uniformity. Your provider will interpret results in the context of your overall health.

Common Conditions Linked to RDW

Elevated RDW is often seen in iron deficiency anemia, vitamin B12 or folate deficiencies, chronic kidney disease, or certain cancers. It can also appear with conditions like hypothyroidism or liver disease.

Reference range

INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A

Specimen: serum

Inform your healthcare provider if you are taking blood thinners. No special preparation required.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

RDW (Guided)

Frequently asked questions

What causes a higher RDW level in my blood test results?
Higher RDW levels can result from conditions affecting RBC production, such as anemia (from iron, vitamin deficiencies, or chronic illness), or from factors that disrupt normal blood cell development.
Can diet affect RDW levels?
Yes, certain diets low in iron, vitamin B12, or folate can influence RBC size and contribute to a higher RDW. Eating balanced meals with these nutrients may help support normal RBC health.
Is RDW always abnormal if it’s elevated?
Not necessarily. While elevated RDW often signals potential issues, it can also appear in healthy individuals without symptoms. Your provider will assess the full clinical picture to determine next steps.
  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