RDW · low result
Low RDW: what it means (and why it is nothing to treat)
Short answer
A low RDW (red cell distribution width) — below the lab's lower limit, typically about 11.5–12% — means your red cells are unusually uniform in size. It has no known medical significance: there is no disease that is diagnosed or treated because the RDW is low, and a low value is if anything a sign of healthy, consistent red cell production. Some analyzers and some lab ranges never report values this low; in others a low RDW is simply the bottom of normal variation. It becomes worth a second look only in one situation — a low MCV with a low or normal RDW, which is the pattern of thalassemia trait rather than iron deficiency — and even then the MCV, not the RDW, is the finding.
Medically reviewed by Youmna DiStefano, MD · Last reviewed November 2026
When does this result need same-day care?
- A low RDW is never urgent.
What is the normal range for RDW?
- age 18+: 11.5 – 14.5 %
Full reference table, citations and testing options: RDW biomarker page.
What are the common causes of low RDW?
- Normal variation — many healthy people run an RDW of 11–12.5%, and some lab ranges start at 11.5 or 12
- Uniform red cell production — the expected state in a well-nourished person with no recent bleeding, deficiency or transfusion
- Thalassemia trait, where small cells are uniformly small (the RDW is normal or low while the MCV is low)
- Anemia of chronic disease, where cells are uniformly normal-sized or slightly small
- Analyzer and reference-range differences — RDW-CV and RDW-SD are different measures with different ranges, and a 'low' flag often reflects the lab's cutoff rather than anything biological
What symptoms go with low RDW?
- None — a low RDW causes no symptoms and is not associated with any condition
What do clinicians usually check next?
- Nothing — a low RDW with a normal hemoglobin and MCV needs no follow-up
- If the MCV is also low, check ferritin; a low MCV with a low or normal RDW and a normal ferritin suggests thalassemia trait, confirmed by hemoglobin electrophoresis
- Read the rest of the CBC as you normally would; the RDW adds nothing when it is low
- Do not repeat the test for the RDW itself
Follow-up tests available at TestWell: Ferritin Test ($21.99).
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 |
|---|---|---|---|---|
| Biological Age Panel | Panel · 3 tests | $59.99 | Yes | 1–3 business days |
| General Wellness Panel | Panel · 4 tests | $49.99 | Yes | 1–3 business days |
| Blood Clotting Panel | Panel · 4 tests | $149.99 | No | 3–7 business days |
| CBC with Differential Test | Test · 14 biomarkers | $17.99 | No | 1–3 business days |
Common questions
Is a low RDW bad?
No. A low RDW means your red cells are very consistent in size, which is normal and if anything favorable. No condition is diagnosed from a low RDW and nothing needs to be done about it.
What does a low RDW mean?
That there is little variation in red cell size — no mix of old and new, small and large cells. It is the expected picture in a healthy person with no recent deficiency, bleeding or transfusion, and in some labs it is just the bottom of the reference range.
Why would my RDW be flagged low?
Usually because the lab's reference range starts at 11.5–12% and your value is a fraction under it. Different analyzers report RDW-CV and RDW-SD with different ranges, so a 'low' flag is more about the cutoff than about you.
Can a low RDW indicate anemia?
Not on its own. Hemoglobin defines anemia, and the MCV and RDW describe the cells. The one pattern worth knowing is a low MCV with a normal or low RDW — small but uniform cells — which points to thalassemia trait rather than iron deficiency, where the RDW is usually high.
Should I retest a low RDW?
No. It will be on every future CBC anyway, and it does not change management. If anything else on the CBC is abnormal, that result is the one to follow.
What is the difference between RDW-CV and RDW-SD?
Two ways of expressing the same spread: RDW-CV is the variation as a percentage of the average cell size (normal roughly 11.5–14.5%), RDW-SD is the actual width in femtoliters (normal roughly 39–46 fL). RDW-CV reads lower when the MCV is large, which is why labs that report both occasionally show one 'low' and the other normal.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.