Omega-3 and omega-6 blood test: reading all 9 results

An omega-3 and omega-6 panel measures the fats from fish and from seed oils in a sample of your whole blood, each as a percentage of the fatty acids in it. Quest Diagnostics' version, the OmegaCheck, measures five fats: EPA, DPA and DHA on the omega-3 side, linoleic acid and arachidonic acid on the omega-6 side. It then adds two totals and two ratios. Those are the nine rows Function Health lists in its membership.¹²

The short version

• One number has published cut-offs: the omega-3 sum (EPA + DPA + DHA). Quest calls 5.5% or more lower risk, 3.8–5.4% moderate and 3.7% or less higher risk. Ranges for the other rows are printed on your report.¹
• A low omega-3 result usually means little fatty fish. Fish, shellfish and fish oil supply EPA and DHA directly. Plant omega-3 adds little to blood levels.³¹
• A high linoleic acid looks like a good sign in the largest studies. Across 30 cohorts, people near the top of the range had about a 22% lower risk of dying from heart and blood-vessel disease than people near the bottom. The omega-6:omega-3 ratio is contested.⁴⁵
• Nothing on this panel is an emergency. It's a slow, diet-driven test, and the numbers depend on the lab's method, so compare like with like.¹⁶

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What this panel measures

Two families of polyunsaturated fats show up on the report.

The omega-3s are EPA, DPA and DHA, the long-chain omega-3s. EPA and DHA come mainly from seafood, especially cold-water fish such as salmon, mackerel and tuna, plus shellfish and fish oil. Algal oils supply DHA.³ DPA sits between the two: the body makes it on the way from EPA to DHA.¹ The plant omega-3, ALA (flaxseed, soybean and canola oils, chia seeds, walnuts), turns into EPA only in small amounts and adds little to blood omega-3 levels, so this panel leaves it out.³¹

The omega-6s are linoleic acid and arachidonic acid. Linoleic acid is the polyunsaturated fat people eat most. It's essential, so it has to come from food: vegetable oils, nuts, seeds, meat and eggs. Soybean oil alone supplies about 45% of the linoleic acid in the U.S. diet.⁷ Since all of it comes from food, your blood level tracks what you eat.⁴

Arachidonic acid comes two ways. The body makes a small amount from linoleic acid, and you eat it ready-made in meat, organ meats and eggs.⁴⁸ The body keeps arachidonic acid under tight control, so its blood level tracks your diet much less closely than linoleic acid does.⁴

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The lab measures each fat as a share of 16 major fatty acids, the ones present in the highest amounts. Then it adds and divides:¹

• Omega-3 total and omega-6 total add up the fats in each family.
• The omega-6:omega-3 ratio divides the sum of six omega-6 fats by the sum of the three omega-3s (EPA, DPA and DHA).
• The AA:EPA ratio divides the arachidonic acid percentage by the EPA percentage.

Quest runs the test on about 1 mL of whole blood in a lavender-top tube. Fasting is preferred but optional.¹

How it differs from the red-cell omega-3 index

The omega-3 index is a separate test, even though both report omega-3s as a percentage:¹⁹

• Sample: this panel uses whole blood; the index uses red blood cells.
• What's counted: this panel's omega-3 sum includes DPA (EPA + DPA + DHA); the index counts EPA + DHA.
• What it's a percentage of: here, 16 major fatty acids, 14 to 22 carbons long; for the index, the fatty acids in red-cell membranes.
• Cut-offs: 5.5% and 3.7% here; 8% and 4% for the index.

Quest reports that the two track each other closely (a correlation of 0.91).¹ They still sit on different scales, so read each result against its own cut-offs.

What's a normal result?

Start with the ranges printed on your report. Quest publishes cut-offs for one number, the OmegaCheck (EPA + DPA + DHA). For every other row, its test directory says "See Laboratory Report".¹

Quest built its cut-offs from quarters of the population it studied:¹

• 5.5% or more: the top quarter, lower risk than people with lower values.
• 3.8–5.4%: the middle half, moderate risk.
• 3.7% or less: the bottom quarter, the highest risk of the three.

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These cut-offs belong to Quest's method. Quest notes that the type of sample changes results.¹ So compare results from the same lab and sample type when you can. None of the sources here split the cut-offs by sex or age.

"Optimal" omega-3 and omega-6 levels: what the targets rest on

Only three of the nine rows have published targets: the omega-3 total and the two ratios. Function Health's public test list names the nine rows but shows no ranges for them.² Here's the ladder, strictest first:

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Why higher omega-3 levels look protective:

• The FORCE consortium pooled 17 cohort studies with 42,466 people followed for a median of 16 years. People in the top fifth of blood EPA, DPA or DHA had a 15–18% lower risk of dying from any cause than those in the bottom fifth (hazard ratios 0.82, 0.84 and 0.85). Plant ALA showed no consistent link.¹²
• In the Physicians' Health Study, which Quest cites for its test, men whose blood long-chain omega-3s were in the top quarter had an 81% lower risk of sudden cardiac death than men in the bottom quarter (relative risk 0.19; 0.28 for the third quarter). It was a smaller study: 94 men who died suddenly and 184 matched controls.¹³¹

What the omega-6 data show:

• The same consortium pooled 30 cohorts with 68,659 people. Comparing the high end of the range with the low end (90th vs 10th percentile), higher linoleic acid went with a 7% lower risk of heart and blood-vessel disease, 22% lower risk of dying from it and 12% lower risk of ischemic stroke (hazard ratios 0.93, 0.78, 0.88). Arachidonic acid showed no link to higher risk; the top fifth had 8% less heart and blood-vessel disease than the bottom fifth.⁴
• A meta-analysis of 13 cohorts and 310,602 people looked at linoleic acid in the diet. The highest intakes went with a 15% lower risk of coronary events and 21% lower risk of coronary death than the lowest.¹⁴

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Trials of omega-3 pills tell a separate, mixed story. These test a product, not a blood level. In VITAL, 1 g a day of marine omega-3s in 25,871 healthy older adults gave a hazard ratio of 0.92 for major cardiovascular events, a difference too small to rule out chance.¹⁵ In REDUCE-IT, 4 g a day of a prescription EPA cut major events from 22.0% to 17.2% in 8,179 statin-treated people with high triglycerides.¹⁶ In STRENGTH, 4 g a day of an EPA-plus-DHA drug matched a corn-oil comparator (12.0% vs 12.2%), and the trial stopped early.¹⁷

Keep "optimal" in perspective. Each target comes from one method: the 2–4 ratio from a textbook written around a different lab's test,¹¹ and the AA:EPA line from plasma in Japanese patients whose average EPA:AA started near 0.6. The JELIS authors wrote that their data fall short of setting definitive target levels.¹⁰

What the two ratios tell you, and where they fall short

The ratios are the most argued-over rows on the panel.

The case for them. Artemis Simopoulos argues that humans evolved eating omega-6 and omega-3 in roughly equal amounts, that Western diets run about 15–17 to 1, and that a lower ratio is more desirable.¹⁸ Those are ratios in the diet. For blood, Quest links a high omega-6:omega-3 ratio and a high AA:EPA ratio with more major coronary events,¹ and JELIS found lower coronary risk with a higher plasma EPA:AA.¹⁰

The case against the omega-6:omega-3 ratio. At a 2006 UK Food Standards Agency workshop, researchers concluded the dietary ratio is "of limited usefulness" and that using it to estimate heart risk "should be abandoned". A ratio can fall because omega-3s went up or because omega-6s went down, and those are different changes.⁵ Quest's own summary says to read the ratio "with caution" for the same reason: it lumps together fats that act differently.¹

The worry about linoleic acid runs through arachidonic acid, which feeds some inflammation-related signaling molecules. In practice, changing linoleic acid intake barely moves blood arachidonic acid. A review of trials found no significant link between arachidonic acid levels and linoleic acid intake, whether intake was cut by up to 90% or raised up to sixfold.⁸ And in the pooled cohorts above, arachidonic acid showed no link to higher risk.⁴

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So when a ratio is high, check which side moved. A low omega-3 total points to diet. A high linoleic acid with an ordinary arachidonic acid is the seed-oil pattern, and the large cohort studies are reassuring about it.

What a low or high result usually means

Low omega-3 total, EPA, DPA or DHA. The usual reason is little fatty fish in the diet.³ Quest notes that foods rich in EPA and DHA, omega-3 supplements and prescription omega-3s all raise the OmegaCheck.¹ The response is large: in a trial of young adults who ate little oily fish, those given 1.8 g a day of EPA + DHA for about 5 months ended with red-cell EPA at 2.46% (vs 0.47% on placebo) and DHA at 7.03% (vs 3.87%).¹⁹

High omega-3 total. Usually regular fatty fish, fish oil or a prescription omega-3. A prescription EPA-only product (icosapent ethyl) leaves a signature: plasma EPA up 635% and DPA up 143%, with DHA unchanged.²¹

High linoleic acid. Usually a diet rich in seed and vegetable oils.⁷ In the pooled cohorts, higher levels went with lower risk.⁴¹⁴

Low or high arachidonic acid. Because the body regulates it tightly, it moves less with diet.⁴ It falls when EPA and DHA rise: 13.6% of red-cell fatty acids on fish oil vs 16.1% on placebo,¹⁹ and down 31% in plasma on prescription EPA.²¹

Low linoleic acid or omega-6 total. True omega-6 deficiency is extremely rare in adults outside an inherited metabolic disorder.⁷ Because each row is a share of the total, a lower omega-6 share can also mean more room taken by other fats, such as omega-3s.¹

Reading the panel with its neighbors

The pattern across EPA, DHA, linoleic acid, arachidonic acid and the omega-6:omega-3 ratio says more than any single row:

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Omega-3s also travel with triglycerides: Quest notes that trials raising EPA and DHA levels have lowered triglycerides.¹

How fast the numbers change

Whole blood mixes fast and slow pools. In a study that gave men fish oil for a year, EPA in plasma cholesterol esters reached half its new level in 4.8 days. EPA in red-cell membranes took 28 days to get halfway and about 180 days to settle.⁶ Quest reports that natural variation in results is highest in plasma, lowest in red cells and in between for whole blood.¹

What that means in practice:

• Plasma fats reflect the past week or two of eating; red cells, the past month or two.⁶ A whole-blood result carries some of each.
• Give a diet change a few months before you judge it on a retest.⁶
• Trends beat snapshots, as long as the lab and sample type stay the same.¹

Going deeper: why the two families are read together

Omega-6 and omega-3 fats share the enzymes that lengthen them. Linoleic acid and ALA compete for the same one, delta-6 desaturase.⁵ Further down the line, EPA competes with arachidonic acid for the enzymes that turn both into short-lived signaling molecules called eicosanoids.²¹ That competition is the idea behind the AA:EPA ratio.

The picture is more mixed than "omega-6 bad, omega-3 good". Arachidonic acid is also the main source of some anti-inflammatory and inflammation-resolving molecules.⁴ And in a controlled diet study, a high-linoleic-acid diet lowered plasma EPA while leaving arachidonic acid, DPA and DHA where they were.²⁰

Questions worth asking

• Which lab and method ran my panel, and does it match my last one?
• Is my omega-3 result a whole-blood OmegaCheck or a red-cell omega-3 index?
• Is my omega-6:omega-3 ratio high because my omega-3s are low or because my omega-6s are high?
• How much fatty fish do I eat in a typical week?
• If I take fish oil or a prescription omega-3, which other labs should we watch, such as triglycerides?
• When would a retest show a change?

FAQ

What is a good omega-3 level on a whole-blood panel? Quest calls an OmegaCheck (EPA + DPA + DHA) of 5.5% or more lower risk, 3.8–5.4% moderate and 3.7% or less higher risk.¹

Is the omega-3 total the same as the omega-3 index? They're different tests. This panel uses whole blood and counts DPA; the index uses red cells and counts EPA and DHA. The cut-offs differ too: 5.5% here, 8% for the index.¹⁹

Is a high linoleic acid bad for you? The large studies point the other way. Across 30 cohorts, higher blood linoleic acid went with lower risk of heart and blood-vessel disease, and a meta-analysis of 13 cohorts linked higher intake to 15% fewer coronary events.⁴¹⁴

What omega-6 to omega-3 ratio should I aim for? It's debated. The Libby app shows 2–4 as optimal, from a functional-medicine textbook. A UK expert workshop called the ratio of limited usefulness and urged attention to omega-3 amounts instead.¹¹⁵

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This guide is for education. It can't diagnose you or replace care from a clinician who knows your history.

Footnotes

1. Quest Diagnostics. OmegaCheck® test summary (Interpretive Guide, test code 92701), content reviewed 9/2025; and the OmegaCheck® test directory listing. The source for the whole-blood specimen, LC/MS/MS method, 16-fatty-acid denominator, ratio formulas, the 5.5% / 3.8–5.4% / 3.7% risk categories for EPA + DPA + DHA, the r = 0.91 correlation with the red-cell index, and "See Laboratory Report" for other ranges. Quest is a commercial laboratory and the test's maker. Test summary · Test listing ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴ ↩²⁵ ↩²⁶ ↩²⁷ ↩²⁸ ↩²⁹

2. Function Health. Nutrients biomarker category page. Lists Omega-3 Total, Omega-3: DHA, DPA and EPA, Omega-6 Total, Omega-6: Arachidonic Acid and Linoleic Acid, the Omega-6/Omega-3 Ratio and the Arachidonic Acid/EPA Ratio, "tested twice a year", without published ranges. Accessed September 24, 2026. A commercial source. functionhealth.com ↩ ↩²

3. National Center for Complementary and Integrative Health. Omega-3 Supplements: What You Need To Know. NIH; last updated November 2024. Food sources of EPA, DHA and ALA. NCCIH ↩ ↩² ↩³ ↩⁴ ↩⁵

4. Marklund M, Wu JHY, Imamura F, et al. Biomarkers of dietary omega-6 fatty acids and incident cardiovascular disease and mortality. Circulation. 2019;139(21):2422–2436. FORCE consortium pooled analysis of 30 cohorts and 68,659 people; linoleic and arachidonic acid levels and heart outcomes. Two authors reported research support from Unilever. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹²

5. Stanley JC, Elsom RL, Calder PC, et al. UK Food Standards Agency Workshop Report: the effects of the dietary n-6:n-3 fatty acid ratio on cardiovascular health. Br J Nutr. 2007;98(6):1305–1310. The workshop's conclusion on the ratio, and the shared delta-6 desaturase. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

6. Katan MB, Deslypere JP, van Birgelen AP, Penders M, Zegwaard M. Kinetics of the incorporation of dietary fatty acids into serum cholesteryl esters, erythrocyte membranes, and adipose tissue: an 18-month controlled study. J Lipid Res. 1997;38(10):2012–2022. 58 men given fish oil for 12 months. PubMed ↩ ↩² ↩³ ↩⁴

7. Whelan J, Fritsche K. Linoleic acid. Adv Nutr. 2013;4(3):311–312. Linoleic acid as the most-eaten polyunsaturated fat, its food sources, soybean oil's share, and the rarity of deficiency. PMC ↩ ↩² ↩³ ↩⁴

8. Rett BS, Whelan J. Increasing dietary linoleic acid does not increase tissue arachidonic acid content in adults consuming Western-type diets: a systematic review. Nutr Metab (Lond). 2011;8:36. Linoleic acid intake cut by up to 90% or raised up to sixfold without a significant link to arachidonic acid levels; arachidonic acid in meat, organ meats and eggs. PMC ↩ ↩² ↩³

9. Harris WS, von Schacky C. The Omega-3 Index: a new risk factor for death from coronary heart disease? Prev Med. 2004;39(1):212–220. Defined the red-cell index and its 8% and 4% zones. PubMed ↩ ↩² ↩³

10. Itakura H, Yokoyama M, Matsuzaki M, et al. Relationships between plasma fatty acid composition and coronary artery disease. J Atheroscler Thromb. 2011;18(2):99–107. JELIS participants; Table 3 gives the EPA:AA cut-offs. DOI ↩ ↩² ↩³ ↩⁴

11. Lord RS, Bralley JA, eds. Laboratory Evaluations for Integrative and Functional Medicine. 2nd ed. Metametrix Institute; 2008. ISBN 978-0967394947. The source of the 2–4 omega-6:omega-3 optimal band as recorded in the Libby app's marker catalog; the book was not opened for this article. ↩ ↩² ↩³ ↩⁴

12. Harris WS, Tintle NL, Imamura F, et al. Blood n-3 fatty acid levels and total and cause-specific mortality from 17 prospective studies. Nat Commun. 2021;12(1):2329. FORCE consortium, 42,466 people; Table 3 gives the top-versus-bottom-fifth hazard ratios. PMC ↩ ↩²

13. Albert CM, Campos H, Stampfer MJ, et al. Blood levels of long-chain n-3 fatty acids and the risk of sudden death. N Engl J Med. 2002;346(15):1113–1118. Physicians' Health Study, men followed up to 17 years. PubMed ↩

14. Farvid MS, Ding M, Pan A, et al. Dietary linoleic acid and risk of coronary heart disease: a systematic review and meta-analysis of prospective cohort studies. Circulation. 2014;130(18):1568–1578. 13 cohorts, 310,602 people. PMC ↩ ↩² ↩³

15. Manson JE, Cook NR, Lee IM, et al. Marine n-3 fatty acids and prevention of cardiovascular disease and cancer. N Engl J Med. 2019;380(1):23–32. The VITAL trial, median 5.3 years. PMC ↩

16. Bhatt DL, Steg PG, Miller M, et al. Cardiovascular risk reduction with icosapent ethyl for hypertriglyceridemia. N Engl J Med. 2019;380(1):11–22. The REDUCE-IT trial. Funded by the drug's maker. PubMed ↩

17. Nicholls SJ, Lincoff AM, Garcia M, et al. Effect of high-dose omega-3 fatty acids vs corn oil on major adverse cardiovascular events in patients at high cardiovascular risk: the STRENGTH randomized clinical trial. JAMA. 2020;324(22):2268–2280. 13,078 patients. PMC ↩

18. Simopoulos AP. The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomed Pharmacother. 2002;56(8):365–379. The main argument for a low dietary ratio. PubMed ↩

19. Flock MR, Skulas-Ray AC, Harris WS, et al. Determinants of erythrocyte omega-3 fatty acid content in response to fish oil supplementation: a dose-response randomized controlled trial. J Am Heart Assoc. 2013;2(6):e000513. 115 healthy young adults who ate little oily fish; Table 5 gives red-cell fatty acids by dose. PMC ↩ ↩² ↩³ ↩⁴

20. Liou YA, King DJ, Zibrik D, Innis SM. Decreasing linoleic acid with constant alpha-linolenic acid in dietary fats increases (n-3) eicosapentaenoic acid in plasma phospholipids in healthy men. J Nutr. 2007;137(4):945–952. 22 men, high- and low-linoleic-acid diets for 4 weeks each. PubMed ↩ ↩² ↩³

21. Ballantyne CM, Manku MS, Bays HE, et al. Icosapent ethyl effects on fatty acid profiles in statin-treated patients with high triglycerides: the randomized, placebo-controlled ANCHOR study. Cardiol Ther. 2019;8(1):79–90. Plasma and red-cell fatty acids on 4 g a day of prescription EPA for 12 weeks. Funded by the drug's maker. PMC ↩ ↩² ↩³ ↩⁴

22. National Library of Medicine. Heart Attack. MedlinePlus. Symptoms, and when to call 911. MedlinePlus ↩