EPA (Eicosapentaenoic Acid)
The amount of EPA, an omega-3 fat found in fish and algae, in your blood. It mostly reflects what you ate or took recently.
AI-drafted. Awaiting verificationAlso called EPA, C20:5n-3, 20:5n-3LOINC 35173-4
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What it is
EPA (eicosapentaenoic acid) is an omega-3 fat found in fatty fish, fish oil and algae-based supplements. Your body can make a little from plant omega-3s, but only in small amounts. EPA helps the body make chemical messengers that play a part in managing inflammation. This test measures the EPA in your blood serum or plasma. It is usually much lower than DHA, and it can change with your most recent meals and supplements.
Why it matters
Blood EPA gives a rough picture of how much omega-3 you have been getting from food and supplements. Clinicians prescribe a purified form of EPA for some people with high triglycerides, but that decision is based on triglycerides and heart risk, not on your blood EPA level. There is no widely accepted target for EPA in serum or plasma, and results differ between labs and methods. EPA is also read together with arachidonic acid (the AA:EPA ratio) and with DHA in the red blood cell omega-3 index.
If it’s low
A low EPA level usually reflects little omega-3 in your recent diet. This is common, especially in people who rarely eat fish. On its own it does not show that anything is wrong, but your clinician can put it in context with your diet and other results.
Common causes
- Eating little or no fish
- A plant-based diet without algae-based omega-3
- Smoking or higher body weight, which are linked to lower omega-3 levels in blood cell studies
- Conditions that make it hard to absorb fat, such as celiac disease or pancreatic problems
What can help
- Eat fatty fish such as salmon, sardines or trout. The American Heart Association suggests two servings of fatty fish a week for people without heart disease
- Ask your clinician whether an omega-3 supplement makes sense for you
If it’s high
A high EPA level usually means you recently ate fatty fish or took fish oil, EPA-rich supplements or a prescription EPA product. It is not a known sign of illness on its own. Lab method and units also affect the number, so compare it with the range printed on your own report.
Common causes
- Fish oil, cod liver oil or EPA-rich supplements
- A prescription omega-3 product containing EPA
- A recent meal rich in fatty fish, if you were not fasting
- Differences in lab method or units
What can help
- Bring a list of the supplements and fish-oil products you take to your next visit
- Ask whether a repeat test after an overnight fast would be useful
What can affect your result
- Recent meals and supplements: fish, fish oil and EPA products can raise serum levels
- Fasting: many labs ask for an overnight fast and no alcohol for 24 hours
- Your usual diet over the past few weeks
- Pregnancy, which shifts fatty acid levels across the trimesters
- Smoking and higher body weight, which are linked to lower omega-3 levels in blood cell studies
- How the lab reports it: an absolute amount (µmol/L) and a percent of total fatty acids are different measurements
- A recent meal, a fish-oil or algae-oil supplement, or alcohol can change serum fatty acid results. Quest's essential fatty acid panel asks for an overnight fast and no alcohol for 24 hours before the draw.
- Labs report this marker in different ways: the absolute amount in the blood (µmol/L, nmol/mL or mg/L), a percent of total fatty acids, or the amount in one fat class such as phospholipids. These are different measurements and should not be compared with each other.
Morning, after an overnight fast, when your lab asks for one. Serum and plasma levels follow recent intake, so they can change fairly quickly after a change in diet or supplements. Red blood cell levels move more slowly and reflect about the past 4 months.
When to talk to a clinician
There is no urgent level for EPA. If your result is far outside the range your lab printed, mention it to your clinician and tell them about any omega-3 supplements or prescription omega-3 products you take.
Questions you could ask
- Which omega-3 test is best for following my results over time?
- Is the amount of omega-3 I take still right for me?
- Would a repeat test after an overnight fast be useful?
- Is my diet giving me enough omega-3, and would a supplement make sense for me?
- Would a red blood cell omega-3 test be a better way to track this?
Questions people ask
Why does my result not have a normal range?
There is no widely accepted normal range for EPA in serum or plasma, and what a lab prints depends on its method and units. If your report prints a range, use that one. Your clinician can help put your result in context.
How is this different from red blood cell EPA?
Serum or plasma EPA mostly reflects recent intake. Red blood cell EPA reflects roughly the past four months and is part of the omega-3 index (EPA plus DHA). The numbers from the two tests cannot be compared.
Why is my EPA so much lower than my DHA?
That is the usual pattern. EPA is typically several times lower than DHA in blood, even in people who eat a lot of fish.
Show the science and sources
Units
- 1 µmol/L = 1 µmol/L
- 1 µmol/L = 1 nmol/mL
- 1 µmol/L = 0.3025 mg/L
For clinicians and researchers
Serum or plasma EPA (20:5n-3) is reported as an absolute concentration of total fatty acid after hydrolysis and methylation of all lipid classes (typically gas chromatography with mass spectrometry or flame ionization; µmol/L or nmol/mL), as a percent of total fatty acids (a separate LOINC, 88997-2), or within one lipid class such as phospholipids. These are not interchangeable. LOINC 35173-4 is the moles/volume code, and no mass/volume EPA code was found. Circulating EPA is typically several-fold lower than DHA and mainly reflects recent intake, so fasting state matters. Red blood cell EPA and the omega-3 index (EPA + DHA as a percent of RBC fatty acids) are preferred for longer-term status, and equations have been published to convert plasma, serum and whole-blood values to RBC equivalents. No consensus reference interval or outcome-based target exists for absolute serum EPA. Published intervals are cohort- and method-specific, for example trimester-specific serum intervals measured by GC-MS in a Spanish pregnancy cohort. The AA:EPA ratio (LOINC 88996-4 gives the inverse molar ratio) is reported separately. Molecular weight is 302.5 g/mol, so 1 mg/L is about 3.31 µmol/L.
LOINC 35173-4 (primary). Specimen: serum-or-plasma.
Sources
- Eicosapentaenoic acid (PubChem CID 5282847), NIH National Library of Medicine (PubChem)
- Fatty Acid Panel, Essential (C12-C22), Serum (test details as listed by Fullscript), Quest Diagnostics
- Over Half of the United States Population Had an Undesirably Low Omega-3 Index Based on Erythrocyte Membrane Measurements: Results From the Cross-Sectional NHANES From August 2021 to August 2023, Current Developments in Nutrition (2026)
- Trimester-Specific Reference Ranges for Saturated, Monounsaturated and Polyunsaturated Fatty Acids in Serum of Pregnant Women: A Cohort Study from the ECLIPSES Group, Nutrients (2021)
- NHANES August 2021-August 2023 Data Documentation: Fatty Acids - Washed RBCs (FAR_L), CDC National Center for Health Statistics (2025)
AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.