What Is the Omega-3 Index, and What Counts as a Good Score?

The Omega-3 Index is a blood test that measures what percentage of the fatty acids in your red blood cell membranes is EPA and DHA. It was proposed in 2004 as a cardiovascular risk marker, and it measures something a supplement label cannot: not what you took, but what your body kept.

What is the Omega-3 Index?

The Omega-3 Index is the combined EPA and DHA content of your red blood cell membranes, expressed as a percentage of the total fatty acids in those membranes.

The choice of red blood cells is what makes the measure useful. Red blood cells live roughly three to four months, and their membranes are built from the fats a person has been eating over that period. So the Index reflects months of intake rather than yesterday's meal or this morning's capsule, which makes it stable enough to compare against itself over time.

It was developed by William S. Harris, an American nutritional biochemist, and Clemens von Schacky, a German preventive cardiologist, and published in Preventive Medicine in 2004 under the title "The Omega-3 Index: a new risk factor for death from coronary heart disease?"

What counts as a good Omega-3 Index score?

An Omega-3 Index of 8% or above is the target the researchers who developed the measure proposed.

In their 2004 analysis, an Index at or above 8% was associated with the greatest protection against death from coronary heart disease, and an Index at or below 4% with the least. The band between 4% and 8% sits in between. Those thresholds came from examining existing studies in which an Omega-3 Index had been recorded or could be calculated, and averaging the levels associated with the greatest protection.

Two things are worth saying plainly about that number. It is a proposed target rather than a formal clinical guideline cut-off, and it has been supported but not formally adopted in the years since. And most people fall well short of it. For scale, the healthy adults enrolled in a 2026 supplementation trial, averaging 53 years old, had a baseline Omega-3 Index of 5.25% before the study began.

Why does the Omega-3 Index differ from the milligrams on a supplement label?

Because they measure two different things. A label reports dose — how many milligrams of EPA and DHA went into the capsule. The Omega-3 Index reports incorporation — how much of that reached your cell membranes and stayed there.

The two do not track one another reliably. How much of a dose is incorporated depends on the oil's molecular form, what it is delivered alongside, and how much processing it has been through. In one 14-week randomized trial, a minimally processed whole salmon oil supplying 100 mg of EPA and DHA per day produced a larger rise in the Omega-3 Index than a concentrated oil supplying 250 mg — two and a half times the dose, and a smaller result.

This is the practical value of the measurement. It is the only one of the two numbers that describes what actually happened in the body.

How long does it take to change your Omega-3 Index?

Months, not days. Because red blood cells turn over across roughly three to four months, the Index responds on that timescale rather than to any individual dose.

This is why most supplementation studies measure at twelve to sixteen weeks. Anyone testing their own Index should expect to wait a comparable period between changing their intake and retesting, and should treat a retest sooner than that as unlikely to show anything meaningful.

How do you get your Omega-3 Index tested?

The Omega-3 Index is not part of standard bloodwork and is not typically ordered at a routine physical. It is available through specialist laboratories, generally as a finger-prick dried blood spot sample collected at home and returned by mail, and through some clinicians on request.

Results come back as a single percentage, usually placed against the risk bands described above. If you are testing in connection with a medication or a diagnosed condition, discuss the result with your doctor rather than interpreting it alone.

Common questions

Is the Omega-3 Index the same as a cholesterol test?

No. A standard lipid panel measures cholesterol and triglycerides circulating in the blood. The Omega-3 Index measures the fatty acid composition of red blood cell membranes. They are separate tests, drawn for different purposes, and one does not substitute for the other.

Can you raise your Omega-3 Index without supplements?

Yes. The Omega-3 Index responds to EPA and DHA intake from any source, and oily fish — salmon, mackerel, sardines, herring — is the most direct dietary route. The reason the supplement category exists at all is that most people do not eat oily fish regularly enough to reach the target through diet alone.

Does a high Omega-3 Index guarantee good cardiovascular health?

No. The Omega-3 Index is a risk marker, which means it is associated with outcomes across populations rather than predictive for an individual. A person with a high Index can still have cardiovascular disease, and a person with a low one may not. It is one measurement among many that a clinician would weigh.

Is the 8% target settled science?

It is the most widely used threshold, and it is a proposed target rather than a formal guideline. It was put forward in 2004 on the basis of the studies available at the time, and later pooled analyses have been broadly consistent with it. It has not been adopted as a clinical cut-off by cardiovascular guideline bodies in the way that blood pressure or LDL targets have been.

Why is the Index based on red blood cells rather than plasma?

Plasma fatty acid levels fluctuate with recent meals, so a plasma measurement largely reflects what a person ate recently. Red blood cell membranes turn over slowly and were judged to be a better reflection of longer-term intake and of other tissues in the body. That stability is the reason the measure was built on red blood cells in the first place.

Sources 

• Harris WS, von Schacky C. The Omega-3 Index: a new risk factor for death from coronary heart disease? Preventive Medicine. 2004;39(1):212-220. DOI: 10.1016/j.ypmed.2004.02.030 — backs the definition, the researchers, the 8% and 4% thresholds, and the rationale for using red blood cells rather than plasma. 

• Utilizing the omega-3 index to assess the relative bioimpact of a whole salmon oil compared to a concentrated omega-3 oil. Functional Foods in Health and Disease, 2026. ClinicalTrials.gov NCT06802068 — backs the 5.25% baseline in adults averaging 53, and the 100 mg versus 250 mg incorporation comparison.