Lab Reference Library / Omega-3 Fatty Acids (Plasma)
Nutritional & Micronutrient
Omega-3 Fatty Acids (Plasma)
EPA · DHA · Plasma Omega-3 Fatty AcidsReference range, optimal functional medicine levels, and how plasma omega-3 fatty acid measurement differs from the Omega-3 Index, when plasma testing is used alongside RBC testing, and what EPA and DHA levels reveal about supplementation adequacy and short-term intake.
Most SearchedMicronutrient
EPA Standard0.2 to 1.8%
DHA Standard1.5 to 4.5%
FM Optimal EPAAbove 1.5%
Units% total FA
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Category: Nutritional & Micronutrient | Also known as: Plasma EPA, Plasma DHA, Plasma Omega-3 Fatty Acids, AA/EPA Ratio
1. What This Test Measures
Plasma omega-3 fatty acids measure the concentration of EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) in blood plasma, expressed as a percentage of total plasma fatty acids. Because plasma fatty acids reflect dietary intake and supplement absorption over the previous 24 to 72 hours rather than stable tissue stores, plasma omega-3 testing serves a complementary but distinct role from the Omega-3 Index, which measures EPA and DHA in red blood cell membranes over 90 to 120 days.
Comprehensive plasma fatty acid panels also measure arachidonic acid (AA), the primary omega-6 derived eicosanoid precursor, allowing calculation of the AA/EPA ratio. This ratio is one of the most clinically informative inflammatory balance markers available, reflecting the real-time competition between pro-inflammatory and anti-inflammatory eicosanoid production at the tissue level.
2. Plasma Omega-3 vs Omega-3 Index: Which to Use When
Plasma Omega-3 (This Test)
- Reflects dietary intake and supplement absorption over the past 24 to 72 hours
- Fluctuates with meals, supplement timing, and fasting status
- Best use: confirming supplement absorption, assessing AA/EPA inflammatory ratio, comprehensive fatty acid panel analysis
- Draw fasting (8 to 12 hours) for reproducible baseline; or 4 to 6 hours post-supplement to confirm absorption
- Not validated as a standalone cardiovascular mortality risk marker
- Available through comprehensive fatty acid panels (LabCorp, Genova, Doctor's Data)
Omega-3 Index (RBC-Based)
- Reflects RBC membrane EPA+DHA over 90 to 120 days; stable long-term marker
- Does not fluctuate with recent meals or supplement timing
- Best use: cardiovascular risk stratification; monitoring long-term omega-3 status; validating supplementation protocol over time
- Can draw any time without fasting; not acutely affected by last dose
- The validated cardiovascular mortality risk marker; below 4% associated with significantly higher cardiac death risk vs above 8%
- Preferred primary omega-3 biomarker for cardiovascular risk assessment
3. Standard and Optimal Ranges
| Marker | Standard Range | FM Optimal | Notes |
|---|---|---|---|
| Plasma EPA | 0.2 to 1.8% total FA | Above 1.0% | Rises acutely with EPA-rich fish oil; sensitive to dose and timing |
| Plasma DHA | 1.5 to 4.5% total FA | Above 3.0% | Higher baseline than EPA; less acutely responsive to supplementation |
| AA/EPA Ratio | US average 10 to 20:1 | Below 3.0:1 | Japanese average is 1.5 to 2.0:1; above 10 reflects pro-inflammatory dominance |
| Total Omega-3 | 2.0 to 6.0% total FA | Above 4.0% | Sum of EPA, DHA, DPA, and ALA in plasma |
Draw fasting (8 to 12 hours) for a reproducible baseline. If confirming supplement absorption, draw 4 to 6 hours after the dose. Avoid fish consumption the day before a baseline draw. Compare repeat draws using the same laboratory platform.
4. The AA/EPA Ratio: The Most Clinically Actionable Plasma Omega-3 Marker
The AA/EPA ratio is the primary reason to order a comprehensive plasma fatty acid panel rather than simply measuring plasma EPA and DHA in isolation. Arachidonic acid (AA) is the precursor to prostaglandins, thromboxanes, and leukotrienes that drive platelet aggregation, vasoconstriction, and immune activation. EPA competes directly with AA for the same COX and LOX enzymes, producing anti-inflammatory and pro-resolving eicosanoids (resolvins, protectins, maresins) instead. The ratio of AA to EPA therefore reflects the balance between inflammatory and anti-inflammatory eicosanoid production in real time.
The average American AA/EPA ratio is 10 to 20:1. The average Japanese ratio is 1.5 to 2.0:1. A functional medicine target of below 3.0 requires a combination of reduced omega-6 seed oil intake and consistent, adequate EPA supplementation of 2 to 4g daily.
5. Why the US AA/EPA Ratio Is So High
- Omega-6 linoleic acid dominance in the food supply: vegetable oils (soybean, corn, sunflower, cottonseed) dominating the US food supply are 50 to 60% linoleic acid (LA); LA converts to arachidonic acid through the delta-6-desaturase pathway; the dramatic increase in seed oil consumption since the 1950s has elevated tissue AA in virtually all Americans not actively supplementing with EPA
- Low dietary EPA and DHA intake: Americans average less than 100 to 200mg EPA and DHA daily from diet; Japanese average 1,000 to 1,500mg daily from traditional seafood-heavy diets; this 5 to 10-fold dietary difference produces proportionally different plasma EPA levels
- Competition at delta-6-desaturase: LA and ALA (plant omega-3) compete for the same rate-limiting enzyme; high LA intake reduces conversion of ALA to EPA and DHA, further suppressing plasma EPA even when plant omega-3 sources are consumed
- Low conversion of ALA to EPA: the conversion of plant-derived ALA (flaxseed, chia, walnuts) to EPA is below 5 to 10% in most adults on high-LA diets; vegans commonly have very low plasma EPA and high AA/EPA ratios despite consuming plant omega-3 sources
6. How to Optimize Plasma Omega-3 and AA/EPA Ratio
Reduce AA (Lower the Numerator)
- Eliminate refined seed oils: replacing soybean, corn, sunflower, and cottonseed oils with olive oil, avocado oil, and coconut oil removes the primary LA precursor to AA; maintained over months, this single change significantly lowers tissue AA
- Eliminate ultra-processed foods: seed oils are ubiquitous in packaged, fried, and fast foods; eliminating these reduces LA intake by 30 to 60% in most Americans
- Reduce conventionally raised meat: grain-fed livestock have much higher AA content than grass-fed; pasture-raised beef and poultry have meaningfully lower AA-to-EPA ratios
- Mediterranean dietary pattern: consistently reduces AA accumulation through reduced seed oil and ultra-processed food consumption alongside increased omega-3 and polyphenol intake
Increase EPA (Raise the Denominator)
- High-dose EPA-rich omega-3 supplementation: 2 to 4g EPA and DHA daily from high-quality fish oil or concentrated EPA supplements; prescription icosapentaenoic acid (Vascepa 4g daily) demonstrated 25% cardiovascular event reduction in the REDUCE-IT trial and dramatically lowers AA/EPA ratio
- Fatty fish consumption: salmon, sardines, mackerel, anchovies, and herring provide 1 to 3g EPA and DHA per serving; 3 to 4 servings weekly delivers meaningful EPA to compete with AA enzymatically
- Algal oil for vegans and vegetarians: algal DHA and EPA bypasses the low ALA-to-EPA conversion problem; the only reliable non-fish direct EPA and DHA source
- Confirmed absorption: re-esterified triglyceride (rTG) form and phospholipid form (krill oil) have superior absorption vs ethyl ester; plasma EPA testing 4 to 6 hours post-dose confirms whether absorption is the limiting factor
Supporting Factors
- Take omega-3 with the largest fat-containing meal: EPA and DHA absorption increases 3-fold when taken with a high-fat meal vs fasting; this is one of the most impactful practical improvements for patients reporting poor omega-3 response
- Vitamin D3 co-optimization: vitamin D3 and omega-3 fatty acids have synergistic anti-inflammatory effects; optimize vitamin D to 60 to 80 ng/mL alongside omega-3 optimization
- Magnesium adequacy: required for delta-6-desaturase enzyme activity; deficiency impairs EPA elongation; optimize RBC magnesium alongside omega-3 supplementation
- Test, dose, retest protocol: plasma omega-3 testing 4 to 6 hours post-dose confirms absorption; Omega-3 Index testing at 8 to 12 weeks confirms long-term tissue saturation is improving toward the above 8% target
7. Related Lab Tests
Omega-3 IndexLong-Term EPA+DHA Cardiovascular Risk Marker
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AA/EPA RatioInflammatory Balance from Same Panel
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hs-CRPOmega-3 Status Influences Systemic Inflammation
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TG/HDL RatioOmega-3s Lower Triglycerides; Improve sdLDL
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MyeloperoxidaseOmega-3s Reduce MPO-Driven Oxidative Stress
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Oxidized LDLEPA Reduces LDL Oxidizability
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8. Clinical Perspective
Clinical Perspective
The AA/EPA ratio is the inflammatory biomarker I find most eye-opening for patients because it translates an abstract nutritional concept into a concrete number that represents how their cells are managing inflammation right now. When a patient comes in eating what they believe is a healthy diet but their AA/EPA ratio is 18:1, I can show them exactly what that means: for every one anti-inflammatory EPA molecule available to their enzymes, there are 18 pro-inflammatory AA molecules competing for the same receptor. That ratio explains their joint pain, their elevated hs-CRP, and their small dense LDL pattern in a single number. And when we retest 90 days after eliminating seed oils and starting 3g EPA and DHA daily, and the ratio is 4.2:1, the patient who was skeptical about omega-3 supplementation can see that they produced a measurable change in their inflammatory biology. That is precision nutrition medicine at its most practical.
Brian Lamkin, DO | Founder, The Lamkin Clinic | Edmond, Oklahoma
9. Frequently Asked Questions
What is the difference between plasma omega-3 and the Omega-3 Index?
Plasma omega-3 reflects dietary intake and supplement absorption over the past 24 to 72 hours and fluctuates with meals and supplement timing. The Omega-3 Index measures EPA and DHA in red blood cell membranes over 90 to 120 days, providing a stable long-term reflection of tissue saturation. The Omega-3 Index is the validated cardiovascular mortality risk marker; plasma omega-3 is used for supplement absorption confirmation and the AA/EPA inflammatory ratio in comprehensive fatty acid panels.
What is an optimal AA/EPA ratio?
A functional medicine target for the AA/EPA ratio is below 3.0:1. The average American ratio is 10 to 20:1, reflecting omega-6 seed oil dominance and low EPA intake. The average Japanese ratio is 1.5 to 2.0:1, achieved through traditional high-fish diets. Ratios above 10:1 reflect significantly pro-inflammatory fatty acid metabolism and are associated with elevated cardiovascular risk, joint inflammation, and metabolic syndrome severity. Achieving below 3.0 typically requires both reduced seed oil consumption and consistent EPA supplementation at 2 to 4g daily.
Does fasting affect plasma omega-3 results?
Yes. Plasma fatty acids rise for 4 to 6 hours after omega-3-containing meals or supplements. For a reproducible baseline, draw fasting (8 to 12 hours) without omega-3 supplements the morning of the draw. If confirming supplement absorption, draw 4 to 6 hours after the supplement is taken. Ensure fasting status is consistent between comparison draws.
Is plant-based ALA sufficient to achieve adequate plasma EPA and DHA?
No. ALA from flaxseed, chia, and walnuts converts to EPA at below 5 to 10% efficiency in most adults, with even lower DHA conversion (below 0.5%). This conversion is further suppressed by high linoleic acid intake competing at the delta-6-desaturase enzyme. Vegans and vegetarians reliably require algal oil supplementation providing direct EPA and DHA to achieve adequate plasma levels and improve their typically elevated AA/EPA ratios.
Why do some patients not respond to omega-3 supplementation?
Poor plasma omega-3 response despite supplementation most commonly results from: taking fish oil in a fasted state (absorption is 3-fold lower without dietary fat), using ethyl ester fish oil with poor bioavailability (re-esterified triglyceride and phospholipid forms absorb significantly better), insufficient dose (below 2g EPA and DHA daily is often inadequate for meaningful AA/EPA improvement), or ongoing high seed oil intake continually replenishing AA faster than EPA can be increased. Plasma testing 4 to 6 hours post-dose confirms whether absorption is the limiting issue.
Content authored and clinically reviewed by Brian Lamkin, DO, founder of The Lamkin Clinic in Edmond, Oklahoma. Brian Lamkin, DO has 25+ years of experience in functional and regenerative medicine. This page reflects current functional medicine practice standards and is updated as new clinical evidence becomes available.
Plasma omega-3 tells you what you ate this week. The AA/EPA ratio tells you how your cells are managing inflammation right now.
A comprehensive fatty acid panel including plasma EPA, DHA, and AA/EPA ratio provides the inflammatory balance picture that standard panels cannot capture. Schedule a consultation for a full omega-3 and fatty acid assessment.
Schedule a ConsultationMedical Disclaimer: This content is provided for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Lab interpretation should always be performed in clinical context by a qualified healthcare provider. Reference ranges and optimal targets may vary based on individual patient history, clinical presentation, and laboratory methodology. Schedule a consultation to discuss your specific results with Dr. Lamkin.