Arachidonic Acid (AA), RBC
How much arachidonic acid, an omega-6 fat, makes up the membranes of your red blood cells, shown as a percent of all the fatty acids there.
AI-verified against cited sources. Awaiting expert reviewAlso called AA RBC, ARA RBC
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The usual range for AA (RBC) depends on age. Add your age above to see where you stand.
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What it is
Red blood cell membranes are built from fats, and their mix reflects what has been in your blood over the past few months. Arachidonic acid (AA) is the main omega-6 fat in these membranes. Labs report it as a percent of all fatty acids in the membrane, not as an amount per volume of blood. Because red blood cells live for about four months, this gives a longer-term picture than a serum or plasma result.
Why it matters
AA is a normal and necessary part of cell membranes, and one AA number says little about health on its own. OmegaQuant notes that AA alone is a poor predictor of health outcomes. It is mostly read with the omega-3 fats EPA and DHA, for example as an AA to EPA ratio. Large studies that followed people over time did not find that higher AA levels raised heart disease risk. When the highest and lowest fifths of AA were compared, the highest fifth had slightly lower risk.
If it’s low
A lower AA percent can reflect a high share of other fats, such as omega-3s, or it can reflect low intake of essential fats or trouble absorbing fat. Clinicians look at AA with the rest of the fatty acid profile before drawing conclusions.
Common causes
- Other fatty acids, such as EPA and DHA, making up a larger share of the total
- Eating very little fat for a long time
- Problems absorbing fat from food
What can help
- Ask your clinician whether your diet or a digestive condition could explain it
- Ask whether the other fatty acids in the profile should be reviewed together
If it’s high
A higher AA percent is not a diagnosis. Because the result is a share of all fatty acids, it also rises when other fats, such as omega-3s, make up a smaller share. Your clinician will usually read it with your other fatty acids and your overall health.
Common causes
- Natural differences in how your body makes AA, including genetics
- Other fatty acids, such as EPA and DHA, making up a smaller share of the total
- Foods or supplements that contain AA itself or gamma-linolenic acid (GLA)
What can help
- Ask your clinician how this result fits with your omega-3 results and your health
- Tell your clinician about supplements such as borage or evening primrose oil, which contain GLA
What can affect your result
- Time: the result reflects roughly the last 3 to 4 months, not today's meal
- 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
- Share of the whole: the result is a percent of all fatty acids, so a change in omega-3s moves the AA percent too
- Genetics: variants in the fatty acid desaturase genes (FADS1 and FADS2) influence how much AA the body makes
- Lab and sample: red blood cell, whole blood and plasma results use different scales and ranges
- A recent blood transfusion mixes donor red cells into your sample, so the result may not reflect your own diet.
- Fasting rules vary by lab and sample type. Quest's whole-blood OmegaCheck says fasting is preferred but not required, and its serum fatty acid panel requires it, so follow your lab's instructions.
- Changes in omega-3 intake (fish, fish oil or algae oil) shift the share of AA over months, because the result is a percent of all fatty acids in the membrane.
Red blood cells live about 4 months, so the membrane fat mix reflects roughly the last 3 to 4 months. OmegaQuant says it takes 3 to 4 months for fatty acid ratios to reach a new level after a change in diet.
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
- Which fatty acid test and sample type should I use so my results can be compared over time?
- How does my AA fit with my EPA and DHA results?
- Could my diet or a digestive condition explain a low result?
- Should we look at the rest of my fatty acid profile?
Questions people ask
Why is my red blood cell AA different from my plasma AA?
They measure different things. Plasma shows a short-term picture and is usually an amount per volume of blood. Red blood cells show about the last 3 to 4 months and are reported as a percent of all fatty acids. The numbers and ranges are not interchangeable.
Should I try to lower my AA?
Not on the strength of this number alone. AA is a normal part of cell membranes, and large studies haven't linked higher levels to more heart disease. Talk with your clinician about what the whole fatty acid profile shows.
Show the science and sources
For clinicians and researchers
Red cell membranes hold AA mostly in phospholipids, and the result is composition (percent of total fatty acids, by weight or area depending on the lab), not concentration. Red cells circulate for months, so the fat mix integrates a long window, which OmegaQuant puts at about 4 months. Methods vary by lab, for example LC-MS/MS on whole blood (Quest OmegaCheck) or dried-blood-spot assays (OmegaQuant). OmegaQuant's whole-blood (dried blood spot) report lists a sample AA reference range of 5.0–14.8% of total fatty acids (about 99% of US adults it measured); that is a whole-blood range and should not be applied to red cell results. No published red cell AA interval was found, so ranges here are left to the lab. Marklund and colleagues pooled 30 prospective cohorts and found no higher cardiovascular risk with higher AA, measured as percent of total fatty acids in several compartments. A systematic review found that changing dietary linoleic acid does not change AA in erythrocyte or plasma/serum phospholipids in adults on Western-type diets.
Sources
- Omega-3 Index Complete Report (sample report, form 103.004v3), OmegaQuant Analytics (2025)
- OmegaCheck (test code 92701), 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)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.