---
title: "What does a high RDW mean?"
type: biomarker-interpretation
url: "https://www.test-well.com/biomarkers/rdw/high"
biomarker: RDW
direction: high
reference_range:
  - "age 18+: 11.5 – 14.5 %"
reviewed_at: 2026-09-06
review_status: reviewed
date_published: 2026-09-05
---

# What does a high RDW mean?

> 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.


## What is the normal range for RDW?

- age 18+: 11.5 – 14.5 %

Often reflects iron, B12, or folate deficiency, or recent blood loss.

## What are the common causes of high RDW?

1. Iron deficiency (early), B12 or folate deficiency
2. Mixed deficiencies, recovery from anemia
3. Recent transfusion, hemolysis
4. Liver disease, alcohol
5. 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 at TestWell: [Ferritin](https://www.test-well.com/tests/ferritin) ($24.99), [Folate (Vitamin B9)](https://www.test-well.com/tests/folate) ($32.99).

## How do you recheck RDW?

| Test or panel | Type | Price | Fasting | Results |
| --- | --- | --- | --- | --- |
| [General Wellness Panel](https://www.test-well.com/tests/general-wellness-panel) | Panel (4 tests) | $89.99 | Yes | 1–3 business days |
| [Blood Clotting Panel](https://www.test-well.com/tests/blood-clotting-panel) | Panel (4 tests) | $149.99 | No | 3–7 business days |
| [Baseline Anemia Panel](https://www.test-well.com/tests/anemia-panel) | Panel (5 tests) | $74.99 | Yes | 2–4 business days |
| [CBC with Differential](https://www.test-well.com/tests/cbc-with-differential) | Test | $21.99 | No | 1–3 business days |

Plus one $6 lab processing fee per order; physician authorization included.

## 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.

## Related

- [RDW reference ranges](https://www.test-well.com/biomarkers/rdw)
- [Hemoglobin reference range](https://www.test-well.com/biomarkers/hemoglobin)
- [Hematocrit reference range](https://www.test-well.com/biomarkers/hematocrit)
- [White Blood Cell Count reference range](https://www.test-well.com/biomarkers/white-blood-cell-count)

## Sources

- [AACC Lab Tests Online](https://www.testing.com/tests/red-blood-cell-indices/)

---

Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-06. Review policy: https://www.test-well.com/editorial-policy

Canonical page: https://www.test-well.com/biomarkers/rdw/high
Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt

Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.