Omega-3 Index
EPA+DHA proportion in red blood cell membranes as a cardiac risk biomarker
Also known as
Definition
The Omega-3 Index is the proportion of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) relative to total fatty acids in red blood cell membranes, expressed as a percentage. It reflects long-term (3-month) omega-3 status and is recognized as a reliable marker of cardiovascular risk. Developed by Harris & von Schacky (2004), it is an independent cardiovascular risk marker alongside LDL and blood pressure.
| Parameter | Value |
|---|---|
| Unit | % |
| Reference Range | < 4% (risk zone) | 4–8% (intermediate zone) | > 8% (upper zone) |
Agree on your personal target range with your doctor.
↓ What a low value means
An Omega-3 Index < 4% corresponds to a risk zone with elevated risk of myocardial infarction and sudden cardiac death (comparable to smoking as a risk equivalent according to von Schacky). Further associations: cognitive impairment, depressive symptoms, elevated inflammatory markers, dry eyes, joint inflammation.
↑ What a high value means
An index > 8% is in the upper zone of the classification proposed by Harris and von Schacky and indicates a high EPA+DHA status. There is no generally accepted normal or cut-off value for even higher values. Omega-3 fatty acids can influence platelet function; whether this matters when anticoagulant medication is taken at the same time is assessed differently across studies (NIH ODS).
✓ What can influence this value
The Omega-3 Index is influenced by the intake of EPA and DHA from fatty cold-water fish (e.g., salmon, mackerel, herring, sardines), algae oil, or fish oil supplements. Individual variability in intake and metabolism is large, and the chemical form of the fatty acids (triglyceride or ethyl ester form) affects absorption. The index reflects the supply over roughly the last three months and therefore changes only slowly. The assessment is made by the treating doctor.
When to test
The index is measured, for example, with known heart disease, family cardiac risk, depression, or cognitive decline, and during supplementation. Because the erythrocyte test reflects an average over about three months, changes in intake show up only with a delay. How often it is measured is decided by your doctor.
Frequently asked questions
What is the difference between the Omega-3 Index and plasma omega-3? +
Plasma fatty acids reflect intake over the past 1–2 days (short-term status). The Omega-3 Index measures EPA+DHA in red blood cell membranes, which live 3 months — making it a long-term marker analogous to HbA1c for blood glucose. The erythrocyte index is more valid for cardiovascular risk assessment.
How quickly does the Omega-3 Index change when intake changes? +
This varies from person to person and depends on genetics, BMI, and baseline level, among other things. Because the index reflects the supply over roughly the last three months, it changes only slowly. People respond very differently to the same intake.
How do algae oil and fish oil compare for the Omega-3 Index? +
Like fish oil, algae oil contains preformed EPA and DHA; fish accumulate omega-3 through algae. Studies show comparable bioavailability and comparable increases in the Omega-3 Index. Algae oil is also a vegan source.
Does a high Omega-3 Index actually protect against heart attack? +
Observational studies consistently show lower cardiovascular event rates with a high Omega-3 Index. REDUCE-IT (icosapent ethyl, high-dose EPA) showed significant reduction in cardiovascular events in high-risk patients. The preventive benefit appears strongest in those with a low baseline index.
Omega-3 Index
Sources
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.