Arachidonic Acid Test · Blood

If you have ever wondered whether the fats you eat are quietly shifting your body toward or away from chronic disease, your arachidonic acid level is one of the clearest answers available. AA (arachidonic acid) is the primary omega-6 fatty acid your cells use to launch inflammatory responses, and the balance between AA and its omega-3 counterparts like EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) is one of the most studied dietary signals tied to heart disease, stroke, and cancer risk.

A standard lipid panel tells you nothing about fatty acid composition. You can have perfect cholesterol numbers and still carry a fatty acid profile that favors chronic inflammation. Measuring AA, ideally alongside EPA and DHA, fills that gap.

What Arachidonic Acid Does in Your Body

AA is a 20-carbon omega-6 fat with multiple double bonds in its structure (a polyunsaturated fatty acid) that sits in the outer layer of virtually every cell in your body. It gets there two ways: directly from animal foods like meat, eggs, and organ meats, or by conversion from linoleic acid (the most common omega-6 fat in vegetable oils) through a series of enzyme steps. Your genetics, particularly variants in the FADS1 and FADS2 genes (fatty acid desaturase genes), strongly influence how efficiently your body makes that conversion.

When a cell is stressed or activated by an immune signal, an enzyme called phospholipase A2 clips AA out of the membrane. Once free, AA becomes the raw material for dozens of signaling molecules collectively called eicosanoids. Some of these, like certain prostaglandins and leukotrienes (molecules that trigger pain, swelling, and fever), ramp up inflammation. Others, like lipoxins, actively calm inflammation down. The net effect depends on which enzymes are most active and what other fatty acids are competing for the same machinery.

This is why AA is not simply "bad." It is more like a volume knob. Too much relative to omega-3 fats, and the inflammatory dial turns up. A healthy proportion, and the system stays in balance. The ratio between AA and EPA in your blood has emerged as one of the more useful ways to gauge that balance.

Heart Disease and Stroke

The largest pooled analysis of omega-6 fatty acid biomarkers and cardiovascular disease, combining data from 30 prospective studies with roughly 69,000 participants, found that higher blood levels of AA were associated with about an 8% lower risk of total cardiovascular events when comparing the top fifth to the bottom fifth of the population. In studies that measured AA in total plasma specifically, the hazard ratio was 0.81 per interquintile range increase (the span between the 10th and 90th percentiles), suggesting about a 19% lower risk. These associations held after adjusting for age, sex, BMI, and other standard risk factors, and showed no consistent differences by age, sex, or ethnicity.

That said, Mendelian randomization studies, which use genetic variants to estimate lifelong exposure, tell a more nuanced story. One such analysis found that genetically predicted higher plasma AA was positively associated with atherosclerotic cardiovascular disease and venous thromboembolism (blood clots in veins), with potentially stronger effects in men than women. Another found that genetically higher AA synthesis was linked to higher apolipoprotein B (ApoB, the protein on "bad" cholesterol particles) and both LDL and HDL cholesterol.

In patients who have already had a stroke, the ratio of EPA to AA matters. A study of 269 people hospitalized for ischemic stroke found that a low EPA/AA ratio, combined with not being on a statin, predicted higher rates of death, recurrent stroke, and new cardiovascular events over follow-up.

Making Sense of the Mixed Signals

These findings can seem contradictory: measured AA looks protective in observational data, but genetically predicted lifelong higher AA looks harmful. The resolution is that measured AA in your blood reflects both what you eat and how your body processes it. People with higher measured AA often have better overall nutritional status and diets rich in protein and micronutrients. The genetic studies isolate the effect of the AA pathway itself, stripped of those dietary confounders. The takeaway is that your AA level is best interpreted not as a standalone number but in context, especially as a ratio with EPA or as part of a full fatty acid profile.

Type 2 Diabetes

A large pooled analysis of 20 prospective cohorts covering 39,740 adults examined omega-6 fatty acid biomarkers and the risk of developing type 2 diabetes. The key finding for AA was essentially neutral: higher AA levels were not associated with increased diabetes risk. The protective signal in that analysis came primarily from linoleic acid, the shorter-chain omega-6 fat that is AA's dietary precursor. A separate study of 4,598 adults in China found that among the omega-6 fatty acids, it was gamma-linolenic acid (GLA, an intermediate between linoleic acid and AA), not AA itself, that was associated with higher diabetes incidence.

Cancer Risk

A Mendelian randomization study using UK Biobank and genetic consortium data found that genetically predicted higher plasma AA was associated with increased risk of colorectal cancer and lung cancer, with a possible link to esophageal cancer. A systematic review of observational studies, however, found that dietary or blood AA was not strongly associated with breast or prostate cancer, and the relationship with colorectal cancer remained unclear from observational data alone.

The difference between genetic and observational findings here mirrors the cardiovascular pattern: lifelong genetically elevated AA may promote tumor-related inflammation over decades, while a snapshot blood level at one point in time may not capture that cumulative effect. If you have a family history of colorectal or lung cancer, knowing your AA level (and your AA/EPA balance) adds a layer of information that standard screening does not provide.

Liver Disease

A Mendelian randomization study found that genetically higher plasma AA may be causally linked to a higher risk of non-alcoholic fatty liver disease (now called metabolic dysfunction-associated steatotic liver disease, or MASLD) and cirrhosis. AA-derived eicosanoids are known to drive fat accumulation and inflammation in liver tissue, and the AA metabolic pathway is considered a therapeutic target in liver fibrosis research.

Heart Failure

In a study of 805 patients with acute decompensated heart failure, researchers built a machine-learning score based on AA and its metabolites that accurately predicted who would die within one year. This AA-based score outperformed several traditional clinical markers for mortality prediction in that population. While this is a specialized clinical application, it signals that AA metabolism carries prognostic weight in serious cardiovascular disease.

Reference Ranges

There are no universally standardized clinical reference ranges for blood arachidonic acid. Most research reports AA as a percentage of total fatty acids (% of total FAs), and results depend heavily on which blood compartment is measured (whole blood, plasma, red blood cell membranes, or cholesterol esters). Your lab may report AA in concentration units or as a percentage, and these numbers are not interchangeable across methods.

The FORCE pooled analysis used quintiles (fifths of the population distribution) rather than fixed cutpoints, with the lowest and highest quintiles spanning a wide range depending on the cohort and specimen type. Because no guideline body has defined "optimal" AA levels, the most useful approach is to interpret your result as a ratio with EPA or within a full fatty acid panel, and to compare your results within the same lab over time.

These are broad orientations, not diagnostic thresholds. Compare your results within the same lab over time for the most meaningful trend.

When Results Can Be Misleading

AA levels reflect your habitual diet over weeks to months, not what you ate yesterday. Still, several factors can distort a single reading:

• Recent diet changes: If you dramatically changed your meat or fish intake in the past few weeks, your result may not yet reflect your new steady state. AA in red blood cell membranes takes about 3 to 4 months to fully stabilize after a dietary shift.
• Genetics: Variants in the FADS1 and FADS2 genes can make your AA level naturally higher or lower regardless of diet. If your level seems out of proportion to your eating pattern, genetic variation is a likely explanation.
• Acute illness or inflammation: Infections and inflammatory flares can transiently shift fatty acid profiles. If you were recently sick, wait at least 2 to 3 weeks before testing.
• Sample handling and lab method: Different labs use different compartments (whole blood, plasma, red cells) and different analytical techniques. A result from one lab is not directly comparable to a result from another. Always retest at the same lab when tracking trends.