Arachidonic Acid (AA)
Measures arachidonic acid, an omega-6 fat in your blood that your body uses to make signaling molecules involved in inflammation and healing.
AI-verified against cited sources. Awaiting expert reviewAlso called ARALOINC 35168-4
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What it is
Arachidonic acid (AA) is an omega-6 fat found in cell membranes all over the body. Your body makes it from linoleic acid, the main omega-6 fat in vegetable oils, nuts and seeds. You also get a little directly from foods such as meat, poultry and eggs. Cells release AA to make short-lived signaling molecules that help control inflammation, blood clotting and healing. This test reports the amount of AA in serum or plasma per volume of blood, which is different from a result given as a percent of all fatty acids.
Why it matters
AA is a normal and necessary part of your body's chemistry, and one AA number says little about health on its own. It is usually read with other fatty acids, such as the omega-3s EPA and DHA, in a panel that checks essential fatty acid status. Large studies that followed people over time did not find that higher blood AA was linked to more heart disease. When the highest and lowest fifths of AA were compared, the highest fifth had slightly lower risk. Very low AA, along with other fatty acid changes, can be a sign of not getting enough essential fats.
If it’s low
A low AA result can reflect a low intake of essential fats, trouble absorbing fat, or long-term intravenous nutrition that doesn't supply enough of them. True essential fatty acid deficiency is rare. Clinicians look at AA with other fatty acids, such as the triene:tetraene ratio, before drawing conclusions.
Common causes
- Eating very little fat for a long time
- Problems absorbing fat from food
- Intravenous (parenteral) nutrition that doesn't supply enough essential fatty acids
What can help
- Ask your clinician whether your diet or a digestive condition could explain it
- Ask whether linoleic acid and the omega-3 fatty acids should be reviewed together
If it’s high
A high AA result is not a diagnosis. Large studies have not shown that higher blood AA raises heart disease risk. Your clinician will usually read it alongside your other fatty acids and your overall health.
Common causes
- Natural differences in how your body makes AA, including genetics
- Foods or supplements that contain AA itself or gamma-linolenic acid (GLA)
- Not following the fasting instructions, since a recent meal changes fatty acid results
What can help
- Ask your clinician how this result fits with your other fatty acid results and your health
- Tell your clinician about supplements such as borage or evening primrose oil, which contain GLA
What can affect your result
- Recent meals and alcohol: Quest asks for an overnight fast and no alcohol for 24 hours before its serum fatty acid panel
- Diet: changing how much linoleic acid you eat has little effect on AA in adults on Western-type diets, but dietary AA and GLA can raise it
- Genetics: variants in the fatty acid desaturase genes (FADS1 and FADS2) influence how much AA the body makes
- Age and sex: Quest requires age and sex to report this panel
- Sample type: serum, plasma, whole blood and red blood cells give different numbers and use different units
- Quest's serum fatty acid panel requires an overnight fast and no alcohol for 24 hours before the draw (children are the exception) and rejects non-fasting samples, so follow your lab's instructions.
- Quest rejects hemolyzed or very fatty (lipemic) samples, and it does not accept serum separator (gel) tubes for this panel.
- Recent changes in diet or supplements that contain arachidonic acid, gamma-linolenic acid or fish oil can shift the fatty acid pattern.
Serum and plasma levels reflect recent intake and metabolism, so the pattern can shift over days to weeks. Red blood cell levels change more slowly, over about 3 to 4 months.
When to talk to a clinician
There is no widely used urgent threshold for AA. Talk with a clinician if a low result comes with a dry, scaly rash, hair loss, brittle nails, slow wound healing or unexplained weight loss, or if you rely on intravenous nutrition.
Questions you could ask
- Is a fatty acid panel useful for my situation?
- How does this result fit with my other fatty acid results?
- Could my diet or a digestive condition explain a low result?
- Should we check my other essential fatty acids?
Questions people ask
Is a higher arachidonic acid level bad?
Not by itself. Large studies that followed people over time did not link higher blood AA to more heart disease. AA is a normal part of your cells, and it's best read with your other fatty acids.
Why does my report show a percent instead of µmol/L?
Labs report AA in two ways: as an amount per volume of blood, or as a share of all fatty acids. They are different measurements with different ranges, so only compare numbers that use the same unit and the same sample type.
Show the science and sources
Units
- 1 µmol/L = 1 µmol/L
- 1 µmol/L = 1 nmol/mL
- 1 µmol/L = 0.3045 mg/L
- 1 µmol/L = 0.3045 µg/mL
Open the Arachidonic Acid unit converter
For clinicians and researchers
AA (20:4n-6) is made from linoleic acid by FADS2, elongase and FADS1. It sits mainly in membrane phospholipids and is released by phospholipase A2 and converted by cyclooxygenase and lipoxygenase enzymes into eicosanoids, which EPA competes with. Serum or plasma 'total' AA includes AA esterified in phospholipids, triglycerides and cholesteryl esters, so an absolute concentration (µmol/L, the same as nmol/mL) moves with overall lipid levels, while AA as a percent of total fatty acids is a different measurement (LOINC 88994-9). AA is the 'tetraene' in the triene:tetraene (Holman) ratio. A threshold of 0.2 is commonly used for essential fatty acid deficiency, but a 2025 review cautions that the ratio alone can mislead, especially with newer lipid emulsions. A pooled analysis of 30 prospective cohorts (FORCE, 68,659 people), which measured AA as a percent of total fatty acids, found no higher cardiovascular risk with higher AA. Reference intervals are lab- and method-specific and Quest's directory lists none ('see laboratory report').
LOINC 35168-4 (primary), 1889-5. Specimen: serum-or-plasma.
Sources
- Fatty Acid Panel, Essential (C12-C22), Serum (test code 11254), Quest Diagnostics
- Biomarkers of Dietary Omega-6 Fatty Acids and Incident Cardiovascular Disease and Mortality, Circulation (2019)
- Increasing dietary linoleic acid does not increase tissue arachidonic acid content in adults consuming Western-type diets: a systematic review, Nutrition & Metabolism (2011)
- Essential fatty acid deficiency in parenteral nutrition: Historical perspective and modern solutions, a narrative review, Nutrition in Clinical Practice (2025)
- Arachidonic acid (PubChem CID 444899), PubChem, National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.