What is Red Cell Distribution Width?
Rather than measuring the actual size of your red blood cells, RDW tracks the variation in sizes between them in a blood sample. Results are expressed as a percentage.
- A low RDW shows that your red blood cells are nearly identical in size and your blood cell production is normal.
- A high RDW reveals a significant mix of oversized and undersized cells, which can help diagnose certain blood disorders like anemia.
Why Does RDW Matter?
Your body operates best when its red blood cells are the same size, allowing oxygen to be delivered smoothly and efficiently. Evaluating RDW levels in a blood test can help doctors:
- Determine anemia types and red blood cell disorders, guiding more precise treatment
- Pinpoint nutritional deficiencies, such as a lack of iron, B12, or folate
- Monitor chronic diseases marked by high inflammation and oxidative stress, such as cardiovascular or chronic respiratory disease
- Evaluate digestive inflammation and disease activity in conditions like inflammatory bowel disease (IBD).1
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How to Interpret RDW?
(Ranges may vary slightly by lab)
Standard reference ranges represent the middle 95% of healthy individuals but don’t necessarily reflect levels associated with longevity. Optimal ranges are derived from clinical guidelines, peer-reviewed research, and real-world outcomes data, with an emphasis on levels associated with peak functioning and reduced disease risk.
Benefits of Optimizing RDW
- Early detection of nutritional deficiencies
- Reduced systemic inflammation and oxidative stress2
- Improved prognosis and reduced mortality risk in those with chronic health problems3
- Better management of chronic health conditions (e.g., heart failure and diabetes)
- Better surgical and post-operative outcomes4
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Low RDW
Low RDW by itself usually indicates a more uniform red blood cell size, which indicates normal blood health. However, when both RDW and MCV are low, it means your red blood cells are uniformly small. This pattern often shows up in inherited blood conditions like thalassemia trait, or in cases of long-standing iron deficiency.
High RDW
High RDW with high MCV means your red blood cells vary in size and tend to be larger than normal, a pattern commonly linked to low vitamin B12 or folate.
High RDW with normal MCV means your red blood cells vary in size but average out as normal, which can happen early in a nutrient deficiency or with liver disease or chronic inflammation.
High RDW often rises early, before anemia develops, making it a valuable early warning marker even when hemoglobin levels are still normal.
Symptoms:
- Fatigue or weakness
- Pale skin
- Shortness of breath
- Dizziness or headaches
Causes:
- Iron-deficiency anemia (often with low MCV) or pernicious anemia
- Chronic diseases such as kidney disease, liver disease, or chronic inflammatory diseases
- Blood loss
- Recent blood transfusions
- High altitude
Healthspan Impacts:
- Chronic inflammation and oxidative stress, which accelerate biological aging5,6
- Increased pro-inflammatory cytokines and oxidative stress, hallmarks of autoimmune diseases7
- Higher risk of frailty and functional decline8
- Increased risk of all-cause and disease-specific mortality
How Hone Treats Out of Range RDW
Your Hone physician will evaluate RDW alongside MCV, iron markers, inflammatory signals, symptoms, and overall health. Treatment for high RDW depends on the root cause.
- Vitamin B12 injections – for pernicious anemia or severe B12 deficiency
- Iron infusion* – for severe iron deficiency
- Management of underlying chronic disease – to address respiratory, intestinal, or cardiovascular issues driving size variation
*Your Hone Physician does not prescribe these treatments but will recommend further evaluation and help coordinate care with your primary care provider when medical treatment is indicated.
- Consume iron-rich foods (beans, lentils, fortified grains)
- Increase B12 (fish, dairy) and folate (leafy greens, legumes) intake
- Stay hydrated
- Quit smoking
- Limit alcohol
- Prioritize 7-8 hours of sleep per night
- Getting regular exercise, including at least one resistance training session/week11
Katsaros, M. et al. (2020). Red cell distribution width as a marker of activity in inflammatory bowel disease: A narrative review. Annals of Gastroenterology.
↑Afzal, M. (2025). Red Cell Distribution Width (RDW) as a Prognostic Marker in Systemic Diseases: A Mini Review. Indian J Hematol Blood Transfus.
↑Li, J. et al. (2018). Relationship of Red Blood Cell Distribution Width with Cancer Mortality in Hospital. BioMed Research International.
↑Frentiu AA, et al. (2023). The Prognostic Significance of Red Cell Distribution Width in Cardiac Surgery: A Systematic Review and Meta-Analysis. J Cardiothorac Vasc Anesth.
↑Fava, C. et al. (2019). The role of red blood cell distribution width (RDW) in cardiovascular risk assessment: Useful or hype? Annals of Translational Medicine.
↑Ananthaseshan, S. et al. (2022). Red blood cell distribution width is associated with increased interactions of blood cells with vascular wall. Scientific Reports.
↑Alghamdi, M. (2023). Red Blood Cell Distribution Width: A Potential Inexpensive Marker for Disease Activity in Patients with Rheumatic Diseases; Scoping Review. Open Access Rheumatology.
↑Li, C.M. et al. (2020). Elevated Red Cell Distribution Width Is Independently Associated With a Higher Frailty Risk Among 2,932 Community-Dwelling Older Adults. Frontiers in Medicine.
↑Semba, R.D. et al. (2010). Serum antioxidants and inflammation predict red cell distribution width in older women: The Women’s Health and Aging Study I. Clinical Nutrition.
↑Otero TMN et al. (2017). Vitamin D Status and Elevated Red Cell Distribution Width in Community-Dwelling Adults: Results from the National Health and Nutrition Examination Survey 2001-2006. J Nutr Health Aging.
↑Loprinzi, P.D. et al. (2015). The association between muscle strengthening activities and red blood cell distribution width among a national sample of U.S. Adults. Preventive Medicine.
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Reviewed for Accuracy by Our Medical Review Board
This biomarker information has been reviewed by a member of Hone’s medical review board. As part of the medical review team, physicians fact-check this content against the latest research and their own experience treating their patients.
Ashley Winter, M.D., is a board-certified urogynecologist trained at Weill Cornell and Cleveland Clinic. She specializes in female and male sexual dysfunction, urinary issues, genital pain, and hormone therapy.
James Staheli, D.O., is the Medical Director for Broad Health, Hone Health’s affiliated medical practice and a family medicine doctor in Atlanta, Georgia.
