Helvy
Full Blood Count
In the UK, the standard clinical (NHS) reference range for Red Cell Distribution Width (RDW) is 11.5-14.5 %, with <13 % considered the performance-optimised range. A result within these ranges suggests typical status; only a qualified clinician can interpret an individual reading.
Red cell distribution width measures how much variation there is in the size of your red blood cells — calculated as the coefficient of variation of the red cell volume curve. Where MCV gives the average size, RDW captures the spread. It is one of the most heavily weighted markers in the Levine PhenoAge composite — small absolute changes have large impacts on the bio-age estimate.
Optimal range · UK
<13 %
Performance-optimised band · clinical (NHS) range 11.5-14.5 %
Clinical (NHS)
11.5-14.5 %
Performance
<13 %
Reference ranges for RDW, not a personal result. Any individual reading should be interpreted by a qualified clinician.
Optimal ranges
| Range | Value |
|---|---|
| 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
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
Low / Deficiency
High / Excess
Dietary sources
Supplementation
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
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
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
This 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.
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