Lab marker
Omega-3 Index
O3I · RBC EPA+DHA
EPA + DHA as a percentage of red-cell fatty acids — the most validated marker of long-term omega-3 status.
What it measures
EPA + DHA as a percentage of total fatty acids in red blood cell membranes. RBCs turn over every ~120 days, so the index reflects the average omega-3 intake over the prior 2–3 months.
Reference context
3 guideline sources
European and North American populations on typical Western diets average 4–5% without supplementation; populations eating 2+ servings of fatty fish weekly average 6–8%. Japanese populations average 9–11%.
Population context — consult guideline targets below
Mechanism
Why moving this marker matters
Membrane EPA/DHA content modulates inflammatory eicosanoid signalling, platelet aggregation, and arrhythmia susceptibility. Higher levels associate with lower cardiovascular and total mortality in prospective cohorts.
Guideline targets
What major guidelines recommend
Harris & von Schacky (cardioprotective)
≥8%
Common reference (intermediate)
4–8%
Common reference (low)
<4%
How to measure
The test, where to get it, when to repeat
Method
Capillary or venous blood draw, then specialised lipid panel (HPLC).
Where
Specialist labs (OmegaQuant in US/EU, Lipid Analytical Laboratories). Less commonly available through standard GP labs.
Typical cost
€40–80 private.
Fasting
Not required
When to test
Common practice
Useful once to establish baseline; repeat 3–6 months after starting or stopping omega-3 supplementation.
Where to test
Independent labs offering this test
Healicus refers you to independent laboratories. You order from the lab; they take the sample, run it, and return your result on their own platform. Healicus never sees your value.
Cerascreen
DE · EUEstablished German home-test catalogue — ISO-certified labs, German-language reports.
Visit Cerascreen
Medichecks
UKUKAS-accredited home blood-test panels with GP-equivalent biomarker coverage.
Visit Medichecks
Thriva
UKApp-first subscription home testing, capillary draw, clinician-reviewed reports.
Visit Thriva
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Context
Reading the numbers
European and North American populations on typical Western diets average 4–5% without supplementation; populations eating 2+ servings of fatty fish weekly average 6–8%. Japanese populations average 9–11%.
Caveats
Sustained intake matters — a one-week burst of fish oil will not move the index. Allow ~12 weeks of consistent intake before retesting.
Practices
What's been shown to influence this marker
EPA/DHA supplementation reliably moves the index 2–4 percentage points over 12 weeks at 1–2 g/day combined dose.
Omega-3 (EPA + DHA)
Supplement·Cardiovascular and cognitive benefits at 1–2g combined EPA+DHA. Skip if you eat 2+ servings of fatty fish weekly.
Why
EPA and DHA are long-chain omega-3 fatty acids primarily from fatty fish. They reduce triglycerides, support cell membrane function, and are concentrated in brain tissue. Supplementation is most useful for people who don't eat fatty fish regularly. Algae-derived versions exist for vegetarians.
How it works
Incorporated into cell membranes; competes with arachidonic acid in eicosanoid synthesis, shifting inflammatory signalling toward resolution.
Expected onset · ~12 weeks for steady-state membrane uptake
How to take
Dosage
1–2g combined EPA+DHA daily (check the label — total fish oil weight is misleading).
Timing
With a meal containing fat
On the label
Look for combined EPA+DHA per serving on the label, not just 'fish oil 1000mg'. Third-party tested for purity (IFOS, USP).
Ideal for
Anyone who eats fatty fish less than twice per week.
Safety
Markers this may influence
Evidence
Where to get it
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See also
Related markers
Take to your physician
Worth discussing
- Whether your index reflects your fish intake or whether supplementation is warranted.
- If supplementing, which form (triglyceride vs ethyl ester) and dose target your level.
- How your O3I fits into your overall cardiovascular risk picture.
Sources
Cited literature
Edited by Carl Pöhl, MD · Healicus editorial
Last reviewed May 2026
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