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AA:EPA Ratio

A ratio of arachidonic acid (an omega-6 fat) to EPA (an omega-3 fat) in your blood. A lower ratio means relatively more EPA.

AI-verified against cited sources. Awaiting expert reviewAlso called AA:EPA, AA/EPA, ARA:EPALOINC 90909-3

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What it is

This ratio divides your arachidonic acid (AA) level by your EPA level. AA is an omega-6 fat. EPA is an omega-3 fat found in oily fish and fish oil. The two compete for the same enzymes in your body, so the balance between them shapes how the body makes signaling molecules that affect inflammation and blood clotting. The ratio goes up when EPA is low. Many studies, especially from Japan, report it the other way round, as EPA:AA.

Why it matters

Studies link a lower EPA:AA ratio, which is the same idea upside down, with a higher risk of heart and blood vessel disease. Those studies show an association, and there is no agreed target for the ratio. OmegaQuant, a lab that reports the AA:EPA ratio, notes that AA alone is a poor predictor of health outcomes. Eating more EPA and DHA from fish or supplements is the most efficient way to lower the ratio, according to OmegaQuant, and it takes about 3 to 4 months to show.

If it’s low

A low ratio means EPA is high compared with AA. This is common in people who eat a lot of oily fish or take fish oil. In studies, the favorable side has been a lower AA:EPA, which is a higher EPA:AA, so a low ratio is not usually a concern on its own.

Common causes

  • Regular oily fish or fish oil intake
  • Taking EPA-containing omega-3 supplements
  • A lower AA level

What can help

  • If you take high-dose omega-3 products, tell your clinician so they can interpret the result

If it’s high

A higher ratio usually means EPA is low compared with AA, which is common in people who eat little oily fish. It isn't a diagnosis. Results from plasma, red blood cells and dried blood spots are on different scales, so your lab's range matters more than any single cut-off.

Common causes

  • Little EPA from oily fish, fish oil or algal oil
  • Natural differences in how your body makes AA and EPA, including genetics
  • A different sample type or lab from the one a range was built on

What can help

  • Ask your clinician whether more oily fish or an omega-3 supplement makes sense for you
  • Re-test with the same lab after about 3 to 4 months if you change your omega-3 intake

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 1.1–69.1 ratio. Source: OmegaQuant Analytics.

Wellness targets

Narrower ranges some clinicians aim for. Being outside one doesn’t mean something is wrong.

2.5–11 ratio (18+). Evidence: Expert opinion. OmegaQuant, a lab, calls 2.5:1 to 11:1 its desirable range and set it to match its desirable Omega-3 Index of 8–12%. Its own FAQ suggests 9 or less for dried blood spots, so even the lab's numbers vary. It was not set from outcome trials, so the evidence is expert opinion.

What can affect your result

  • Omega-3 intake: EPA from oily fish, fish oil, krill oil or algal oil lowers the ratio, and it takes about 3 to 4 months to reach a new level
  • Sample type and method: plasma, red-cell and whole-blood ratios are not on the same scale
  • Which way round it is shown: AA:EPA and EPA:AA are the same measurement upside down
  • Genetics: variants in the fatty acid desaturase genes (FADS1 and FADS2) influence AA and EPA levels
  • Omega-3 intake lowers the ratio. Eating oily fish or taking fish oil, krill oil or algal oil before the test can change EPA, and stopping or starting them changes the ratio over about 3 to 4 months.
  • Quest's OmegaCheck asks for a 1 mL EDTA whole-blood sample that is gently inverted, never shaken or centrifuged, and kept refrigerated, and it rejects very fatty (lipemic) samples.
  • The sample type changes the scale. Plasma, red-cell and whole-blood ratios are not interchangeable, so compare results only from the same lab and method.

About 3 to 4 months for the ratio to reach a new level after a steady change in omega-3 intake (OmegaQuant).

When to talk to a clinician

There is no urgent threshold for this ratio. Mention it at your next visit if your result is far outside your lab's range or if you are changing your omega-3 intake.

Questions you could ask

  • Which lab and sample type should I use so my results can be compared over time?
  • Does my omega-3 intake from fish or supplements make sense for me?
  • Should we recheck in a few months using the same lab?
  • Does my fish oil or fish intake explain this result?

Questions people ask

What is the difference between AA:EPA and EPA:AA?

They are the same measurement upside down. An AA:EPA of 10 is an EPA:AA of 0.1. Papers from Japan often use EPA:AA, so check which one your report shows.

Why does my ratio differ between labs?

Plasma, red blood cells and whole blood hold different mixes of fats, and labs use different methods. OmegaQuant's whole-blood range is 1.1 to 69.1 with a desirable range of 2.5 to 11, while Quest's report gives its own range. Compare results from the same lab over time.

How long does it take to change my ratio?

About 3 to 4 months of steady omega-3 intake, according to OmegaQuant. Re-testing sooner may not show the full change.

Show the science and sources

For clinicians and researchers

AA and EPA compete as substrates for cyclooxygenase and lipoxygenase enzymes, so EPA yields less inflammatory eicosanoids than AA, and the EPA:AA ratio has been studied as a marker of chronic inflammation and cardiovascular risk (Nelson and Raskin, 2019), with lower EPA:AA associated with coronary disease, myocardial infarction, stroke, heart failure and peripheral artery disease in epidemiologic studies. Thresholds for treatment are still being defined. Labs differ in what they measure. OmegaQuant reports a ratio from dried-blood-spot (whole blood) percent-of-total-fatty-acids values with a reference range of 1.1:1 to 69.1:1 (taken from about 75,000 samples from people of unknown health, and covering about 99% of them) and a desirable range of 2.5:1 to 11:1, picked to correspond to its Omega-3 Index target of 8–12%. Its FAQ gives slightly different targets: 9 or less for dried blood spots and 15 or less for red-cell assays. Quest's OmegaCheck (LC-MS/MS on EDTA whole blood) reports an AA/EPA ratio with ranges given only on the report. LOINC 90909-3 is a mass ratio in blood. Because AA (304.5 g/mol) and EPA (302.5 g/mol) have nearly the same molecular weight, mass and molar ratios differ by under 1%. LOINC 88996-4 is the inverse, EPA/AA as a molar ratio in serum or plasma, and is not interchangeable with this value. Japanese studies commonly use EPA:AA.

LOINC 90909-3 (primary). Specimen: calculated.

Sources

  1. Omega-3 Index Complete Report (sample report, form 103.004v3), OmegaQuant Analytics (2025)
  2. OmegaQuant FAQ (reference ranges and the ratios included in the profile), OmegaQuant Analytics
  3. The eicosapentaenoic acid:arachidonic acid ratio and its clinical utility in cardiovascular disease, Postgraduate Medicine (2019)
  4. OmegaCheck (test code 92701), Quest Diagnostics

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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