RDW · high result
What does a high RDW mean?
Short answer
A high RDW means red cells vary more than usual in size. It's an early sign of nutritional deficiency — iron, B12 or folate — often before hemoglobin or MCV change, and rises after transfusion, in hemolysis, liver disease and mixed anemias. A high RDW with a low MCV favors iron deficiency over thalassemia trait (which usually has a normal RDW). It is also a non-specific marker that tracks inflammation and general health in research.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
What is the normal range for RDW?
- age 18+: 11.5 – 14.5 %
Often reflects iron, B12, or folate deficiency, or recent blood loss.
Full reference table, citations and testing options: RDW biomarker page.
What are the common causes of high RDW?
- Iron deficiency (early), B12 or folate deficiency
- Mixed deficiencies, recovery from anemia
- Recent transfusion, hemolysis
- Liver disease, alcohol
- Chronic inflammation, heart failure
What symptoms go with high RDW?
- None from RDW itself
What do clinicians usually check next?
- Ferritin, B12, folate
- Reticulocyte count and peripheral smear
- Interpret with MCV and hemoglobin
Follow-up tests available at TestWell: Ferritin ($24.99), Folate (Vitamin B9) ($32.99).
How do you recheck RDW?
Prices are cash-pay; every order adds one $6 lab processing fee. Physician authorization is included; no insurance or referral needed.
| Test or panel | Type | Price | Fasting | Results |
|---|---|---|---|---|
| General Wellness Panel | Panel · 4 tests | $89.99 | Yes | 1–3 business days |
| Blood Clotting Panel | Panel · 4 tests | $149.99 | No | 3–7 business days |
| Baseline Anemia Panel | Panel · 5 tests | $74.99 | Yes | 2–4 business days |
| CBC with Differential | Test · 14 biomarkers | $21.99 | No | 1–3 business days |
Common questions
High RDW but everything else normal — does it matter?
Often it's the first hint of a developing iron, B12 or folate deficiency, so those three tests are worth checking. On its own it doesn't need treatment.
Sources
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.