Optimal Ranges
What is the optimal range for RDW?
Clinical (NHS) Range
11.5-14.5 %
%
Performance-Optimised Range
<13 %
%
| Range | Value | Unit |
|---|---|---|
| Clinical (NHS) reference range | 11.5-14.5 % | % |
| Performance-optimised range | <13 % | % |
The clinical range defines what is considered medically “normal” — broad enough to cover 95% of the population. The performance range reflects where research and clinical experience suggest most people feel and function at their best. A result in either range suggests typical status and is not a diagnosis; any individual reading should be interpreted by a qualified clinician.
Why It Matters
Why RDW matters for performance
RDW is one of the most underappreciated longevity markers in routine bloodwork. It rises in iron deficiency before haemoglobin falls, rises in B12 deficiency before MCV climbs, and rises non-specifically with chronic inflammation, oxidative stress, and bone marrow stress. Beyond anaemia, an RDW above 14.5% is independently associated with higher all-cause mortality across virtually every age and disease group studied. The longevity-friendly target is below 13%.
Symptoms
What are the symptoms of low or high RDW?
Low / Deficiency
- RDW is not symptomatic by itself
- Low RDW is unusual and usually not clinically meaningful
High / Excess
- Often asymptomatic until the underlying anaemia advances
- Fatigue, breathlessness on exertion (when anaemia develops)
- Reduced exercise tolerance
- Cold hands and feet (iron pattern)
Dietary Sources
Which foods support RDW levels?
Supplementation
How do you improve RDW levels?
RDW is a downstream signal — it doesn't respond to direct supplementation, only to fixing what's driving the variation. The work-up follows ferritin, B12, folate, and hs-CRP. Once the underlying cause is corrected, RDW normalises over 8-12 weeks as the older heterogeneous red cells are replaced. Retest at 12 weeks after any intervention.
Testing
How is RDW tested in the UK?
RDW is measured from a blood sample. With Helvy, that means a finger-prick kit taken at home and posted to a UKAS-accredited UK laboratory, with results in around 5 days, reviewed by a qualified clinician. Your result is reported against both the clinical range (11.5-14.5 %) and the performance-optimal range (<13 %), so you can see not just whether you are “normal” but whether you are optimal. If you make a change, retest after 8-12 weeks to confirm it worked.
Research
Key study
An epigenetic biomarker of aging for lifespan and healthspan
Levine ME, Lu AT, Quach A, et al.
Aging (Albany NY) (2018)
DOI: 10.18632/aging.101414Related Biomarkers
Related Guides
Explore RDW in depth
Test your RDW levels
RDW is included in the Helvy 50+ biomarker panel. Get your results in 5 days with a personalised protocol.
Order Your TestThis content is for educational purposes only and does not constitute medical advice. Your data suggests areas for optimisation, but any concerns should be discussed with a qualified healthcare professional. If your results flag values outside safe ranges, we recommend consulting your GP.