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RDW (Red Cell Distribution Width)

⚠️ Update approaching🔬 Evidence: ModerateHematology
Diğer adları: RDW-CV, RDW test, Red cell distribution width
⚠️

Discuss your test results with your doctor. This page is for informational purposes only and does not provide a diagnosis.

⚡ Key Facts

• Measures the variation in red blood cell size (anisocytosis) • Normal: RDW-CV 11.5–14.5% • Helps distinguish iron deficiency (high RDW) from thalassemia trait (normal RDW) • Increasingly studied as a prognostic marker in various conditions

🧪 What Does This Test Measure?

RDW (red cell distribution width) measures the degree of variation in red blood cell sizes, helping distinguish iron deficiency anemia from thalassemia trait.

📋 Why Is It Ordered?

Ordered for anemia differential diagnosis, distinguishing iron deficiency from thalassemia, and monitoring nutritional deficiency treatment response.

🔧 Preparation

Part of the CBC. No special preparation is required.

📊 Reference Ranges

Normal: RDW-CV 11.5–14.5% Elevated: >14.5% (anisocytosis — red blood cell size variation) ⚠️ Reference ranges vary by laboratory.

⬆️ High Values

Elevated RDW may be associated with iron deficiency anemia, B12 or folate deficiency, hemolytic anemia, recent transfusion, or mixed nutritional deficiencies.

⬇️ Low Values

Low RDW is generally not clinically significant. It indicates homogeneous red blood cell sizes.

⚙️ What Can Affect Results?

Blood transfusion, post-iron treatment changes, sample storage time, cold agglutinins, and reticulocytosis may affect RDW results.

🔬 Evidence Summary

Moderate evidence: 1 guideline, 1 systematic review, and 3 reviews/observational studies.

📚 Most Important Studies on This Topic

1

Laboratory diagnosis of anemia: are the old and new red cell parameters useful in classification and treatment, how?

Review· International Journal of Laboratory Hematology · 2016 · PMID: 27195903

2

Iron-deficiency anemia

Review· N Engl J Med · 2015 · PMID: 25946282

3

Guideline on haemoglobin cutoffs to define anaemia in individuals and populations

Guideline· World Health Organization · 2024 · PMID: 38530913

✅ Key Takeaways

💡

What you learned: RDW quantifies red blood cell size variation. It is particularly useful for distinguishing iron deficiency from thalassemia trait.

⛔

RDW alone cannot diagnose anemia type. It should be interpreted alongside MCV, iron panel, and clinical context.

🔬 Sources Used on This Page

5 sources · Most recent publication: 2024
📋
Guideline
Expert society and guideline recommendations
1
source
📊
Systematic review / meta-analysis
Combined analysis of multiple studies
1
source
📖
Review
Comprehensive topic evaluation
2
sources
👁
Observational
Observational and cohort studies
1
source
Overall assessment: Evidence level for this topic is strong. This page is supported by 1 guideline, 1 systematic review/meta-analysis, 2 reviews, 1 observational study.

📝 Questions to Ask Your Doctor

Be prepared for your appointment. Add questions to your list.

📋 References

[PMID: 38530913] Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. World Health Organization, 2024.
[PMID: 38432242] Haemoglobin thresholds to define anaemia from age 6 months to 65 years: estimates from international data sources. Lancet Haematology, 2024.
[PMID: 27195903] Laboratory diagnosis of anemia: are the old and new red cell parameters useful in classification and treatment, how?. International Journal of Laboratory Hematology, 2016.
[PMID: 25946282] Iron-deficiency anemia. N Engl J Med, 2015.
[PMID: 24297872] A systematic analysis of global anemia burden from 1990 to 2010. Blood, 2014.
Last reviewed: 4/2/2026
Next review: 4/2/2027

⚖️ Comparisons

MCV vs RDW→

🔗 Related Topics

🧪 MCV (ortalama eritrosit hacmi)🧪 Hemoglobin🧪 Hemogram (tam kan sayımı)🧪 Ferritin (demir depoları)
⚖️ This page does not replace medical advice. Make treatment decisions with your doctor.
Content is based on scientific studies indexed in PubMed and current clinical guidelines.