Blood WorkRDW (red cell distribution width) shows how much your red blood cells vary in size. It's part of a complete blood count (CBC), and the typical range is about 11.5% to 15%. A high RDW means your red cells vary more in size than usual, often from early iron deficiency, low B12 or folate, or recent bleeding; a low RDW is rarely a concern. RDW is most useful read with MCV.
What does RDW measure?
Healthy red blood cells are mostly the same size. RDW measures how much they vary. When your body is short of iron, B12 or folate, or is replacing lost blood, it makes cells of different sizes, and RDW rises, sometimes before other numbers change.
What is a normal RDW?
| Result | What it usually means |
|---|---|
| Below about 11.5% | Low: cells are very uniform. Rarely a concern. |
| About 11.5% to 15% | Typical adult range. |
| Above about 15% | High: red cells vary in size. Read with MCV to find the cause. |
Your lab's printed range applies; labs report RDW-CV (a percentage) and sometimes RDW-SD (in fL).
What does high RDW mean?
| High RDW with... | Common causes |
|---|---|
| Low MCV (small cells) | Iron deficiency, the most common pattern. |
| High MCV (large cells) | Low vitamin B12 or folate, liver disease, or a burst of young red cells after bleeding. |
| Normal MCV | Early iron, B12 or folate deficiency, two deficiencies at once, recent blood loss or transfusion. |
Large studies link a high RDW with a higher risk of heart disease and other conditions, but RDW isn't used to diagnose any of them; it's a reason to look at the whole picture.
If your blood count also shows anemia, call 911 or go to the ER for chest pain, fainting or severe shortness of breath, and get care the same day for black or bloody stools.
What does low RDW mean?
A low RDW means your red cells are unusually uniform in size. On its own it isn't linked to any disease and doesn't need treatment.
If your RDW is high at Passion Health
A Texas-licensed clinician reviews every result and calls you the same day about anything critical. One result outside the range is common and often harmless; we read it with the rest of your panel, your history and your medicines, and recheck when that's the sensible next step.
We look at your MCV and hemoglobin, then usually check ferritin, B12 and folate. The Energy & Iron Panel ($119) covers all three with a blood count.
RDW test cost in Texas
Self-pay. RDW comes with every complete blood count. In Essential Blood Work ($59) it's part of 33 results with the draw and a clinician's review included; on its own, the complete blood count is $20 plus the $29 draw and review fee ($49).
With insurance. If we're in network with your plan, we bill it when the test is covered. You pay cash for a test only after we tell you the price in writing, and Medicare patients sign an Advance Beneficiary Notice first.
RDW blood test questions
What is RDW in a blood test?
RDW, red cell distribution width, measures how much your red blood cells vary in size. It's part of a complete blood count, and the typical range is about 11.5% to 15%.
What does a high RDW mean?
Your red cells come in a mix of sizes. Common causes are iron deficiency, low B12 or folate, and recent bleeding. Your clinician reads it with MCV to narrow it down.
What does a low RDW mean?
Your red cells are very uniform in size. A low RDW on its own isn't a sign of disease.
Is a high RDW serious?
Often not. A slightly high RDW with a normal blood count may just mean early low iron. It's worth checking ferritin, B12 and folate, especially if you're tired.
Can high RDW be a sign of cancer?
RDW isn't a cancer test. It can be raised in many conditions, most often simple nutrient deficiencies. A clinician looks at the rest of your blood count and your symptoms to decide whether anything more is needed. If a high RDW turns out to be iron deficiency, men and women after menopause usually need a stomach and colon check, since slow bleeding is a common cause.