RDW Blood Test
What Is RDW?
Red cell distribution width, or RDW, measures how much your red blood cells vary in size. In a healthy person, red blood cells are fairly uniform. When RDW is elevated, it means there is more variation, with some cells larger or smaller than normal. This variation often signals that your body is struggling to produce healthy red blood cells. It can also mean cells are being destroyed too quickly.
RDW is reported as a percentage, with a typical reference range of 11.5% to 14.5%. The measurement reflects the coefficient of variation in red blood cell volume. Your RDW is tested as part of a complete blood count. It helps identify different types of anemia and nutritional deficiencies. Lower RDW values closer to 11.5% generally reflect healthier, more uniform red blood cells.
Why Test RDW?
- Screen for anemia and identify the type of anemia present
- Detect nutritional deficiencies in iron, vitamin B12, or folate
- Monitor chronic inflammation or inflammatory diseases
- Investigate persistent fatigue, weakness, or unexplained tiredness
- Assess gut health and nutrient absorption issues
- Track recovery after treating anemia or nutritional deficiencies
- Understand root causes before starting medication
Normal RDW Levels
| Category | Range | Interpretation |
|---|---|---|
| Optimal | 11.5% to 13.0% | Healthy, uniform red blood cells with good production |
| Normal | 13.1% to 14.5% | Acceptable variation, typically no concern |
| Borderline | 14.6% to 15.5% | Mild variation, may indicate early nutritional gaps |
| Elevated | Above 15.5% | Significant variation, investigate for anemia or deficiencies |
Symptoms of Abnormal RDW
High RDW itself does not cause direct symptoms, but it reflects underlying conditions that do. Symptoms related to elevated RDW usually stem from anemia or nutritional deficiencies. These can include persistent fatigue, weakness, pale skin, and shortness of breath with mild exertion. You might also experience dizziness, cold hands and feet, brittle nails, or frequent headaches. Difficulty concentrating and restless legs are common too. In cases of vitamin B12 deficiency, you might notice tingling or numbness in the hands and feet, balance problems, or mood changes.
Low RDW is typically not associated with symptoms and is generally considered normal or even favorable. It indicates that your red blood cells are uniform in size. This usually means healthy red blood cell production. In rare cases where low RDW appears with other abnormal blood counts, symptoms would relate to the underlying condition rather than the RDW itself.
What Affects RDW Levels
When your body lacks key nutrients like iron, vitamin B12, or folate, it produces red blood cells of different sizes as it tries to compensate. Chronic inflammation, liver disease, or conditions that affect red blood cell production can cause increased variation. Poor gut health can prevent proper absorption of iron and B vitamins even if dietary intake seems adequate. Conditions like celiac disease, Crohn's disease, or low stomach acid reduce nutrient absorption significantly.
Chronic stress, inflammatory foods, alcohol use, and certain medications can also affect red blood cell production. Medications like metformin, proton pump inhibitors, and some antibiotics interfere with B vitamin absorption. Heavy menstrual periods or internal bleeding can deplete iron stores over time. From a root-cause perspective, elevated RDW often points to nutritional gaps or underlying inflammation. It is worth investigating diet quality, gut health, and absorption issues before jumping to medication.
How to Improve Your RDW
- Eat iron-rich foods like grass-fed beef, liver, dark leafy greens, and pumpkin seeds
- Pair iron sources with vitamin C foods like citrus, bell peppers, or berries to improve absorption
- Include B12 sources such as eggs, wild-caught fish, and pasture-raised poultry
- Add folate-rich foods like lentils, beans, asparagus, and avocado to your meals
- Support gut health with fermented foods like sauerkraut, kimchi, and kefir
- Limit alcohol consumption, which depletes B vitamins and damages red blood cells
- Reduce inflammatory foods such as refined sugar, processed oils, and fried foods
- Consider supplementing with iron, B12, or folate if testing shows deficiency
- Address digestive issues with a healthcare provider to improve nutrient absorption
- Manage chronic stress through sleep, movement, and relaxation practices
Related Tests
Test Your RDW Levels Today
Get your RDW results in 24 to 48 hours. No doctor visit needed. Order online, visit a Quest Diagnostics location near you, and receive your results securely.
- Results in 24 to 48 hours
- Over 2,000 Quest locations nationwide
- No doctor visit or appointment needed
- Secure online results you can share with your provider
Screen for 1,200+ health conditions
Start with a simple check-in, get personalized insights, explore guided care options. All in one place. Your annual health roadmap
FAQ
RDW stands for red cell distribution width. It measures the variation in size of your red blood cells. A higher percentage means your cells vary more in size, which often signals anemia or nutritional deficiencies. Lower values indicate more uniform, healthier red blood cells.
The typical reference range for RDW is 11.5% to 14.5%. Values closer to the lower end, around 11.5% to 13%, are considered ideal. They indicate healthy, uniform red blood cells. Values above 14.5% suggest increased variation and may require further investigation.
High RDW is most commonly caused by nutritional deficiencies in iron, vitamin B12, or folate. Chronic inflammation, liver disease, and conditions affecting red blood cell production can also elevate RDW. Poor gut health that prevents nutrient absorption is another common root cause.
Yes, diet has a direct impact on RDW levels. Eating iron-rich foods, B vitamins, and folate helps produce uniform red blood cells. Poor nutrition or diets lacking in key nutrients lead to varied red blood cell sizes. Inflammatory foods and excessive alcohol can also raise RDW.
High RDW is not immediately dangerous but signals an underlying issue that needs attention. It often points to anemia or nutritional deficiencies that can worsen if left untreated. Addressing the root cause early prevents more serious complications. Work with your healthcare provider to investigate further.
RDW measures variation in red blood cell size, while MCV measures average red blood cell size. Together, they help identify the type of anemia present. High RDW with low MCV suggests iron deficiency, while high RDW with high MCV points to B12 or folate deficiency.
Chronic stress can indirectly affect RDW levels by impacting nutrient absorption and increasing inflammation. Stress depletes B vitamins and can disrupt gut health. This leads to nutritional deficiencies that raise RDW. Managing stress supports better red blood cell production.
Do not start iron supplements without testing first. High RDW can be caused by iron deficiency, but it can also result from B12 or folate deficiency. Taking iron when you do not need it can cause harm. Get iron studies and vitamin levels checked before supplementing.
It typically takes 8 to 12 weeks to see improvement in RDW after addressing nutritional deficiencies. Red blood cells live about 120 days, so changes take time. Consistent dietary changes, supplementation if needed, and addressing gut health all support faster recovery.
Yes, certain medications can raise RDW by interfering with nutrient absorption. Metformin reduces B12 absorption, while proton pump inhibitors lower stomach acid needed for iron and B12. Some antibiotics and chemotherapy drugs also affect red blood cell production. Discuss medication effects with your provider.
Still got questions?
Our team is here to help. Call us at 863-270-9911 or email [email protected]