Can this result diagnose a condition on its own?

No. A laboratory result should be interpreted with related tests, symptoms, medical history, and the reference information on the report.

Which reference range should I use?

Use the reference interval provided by the laboratory that performed the test. Clinical decision cutoffs, when relevant, are shown separately.

When should I discuss the result with a healthcare professional?

Professional assessment is appropriate when a result is markedly outside the reference interval, serious symptoms are present, an abnormality persists or recurs, or follow-up has been recommended.

Information about a laboratory test

RDW: What Does This Blood Test Measure?

Shows how much red blood cell sizes vary from one another.

Test summary

Test name: RDW
Abbreviations: RDW, RDW-CV, RDW-SD
Category: Hematology
Panel: RBC Indices / Hemogram
Specimen: Whole blood
Common units: %, fL (RDW-SD)

What does the test measure?

Shows how much red blood cell sizes vary from one another.

Why is the test ordered?

Often used with MCV and other red-cell indices when investigating the pattern or possible cause of anemia.

Information about a low result

A low RDW means red blood cells are relatively similar in size and, by itself, is usually not considered a concerning finding.

Information about a high result

A high RDW means there is greater variation in red blood cell size and can occur in several anemia patterns.

Reference and clinical context

Use the reference interval printed on your own laboratory report first. Reference intervals may vary by laboratory, method, unit, age, sex, pregnancy, specimen, and other conditions. Numeric records in this workbook are explicitly labeled as either source-based example reference intervals or clinical decision cutoffs.

Reference ranges may vary by laboratory, method used, age, sex, pregnancy status, and clinical context. The reference range on your own laboratory report takes precedence.

Interpretation notes

RDW does not establish a diagnosis on its own; it is more meaningful with MCV, hemoglobin, ferritin, and other blood-test results.

Related specialties

Hematology
Internal Medicine

Frequently asked questions

More information about this test

High RDW: What Does It Mean?

Sources

Red Blood Cell (RBC) Indices — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2024 · MCV, MCH, MCHC, RDW definitions and interpretation · Verified: Aug 11, 2026
RDW (Red Cell Distribution Width) — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2024 · RDW interpretation; low RDW usually not concerning; combine with other indices · Verified: Aug 11, 2026
Ferritin Blood Test — U.S. National Library of Medicine (MedlinePlus)
Government medical reference · 2025 · Ferritin purpose; low/high context; inflammation and liver-related causes of elevation · Verified: Aug 11, 2026