You can test for ALDH2 deficiency through genetic testing, an ethanol patch test, or a flushing questionnaire. Genetic testing is the most accurate option, identifying the specific gene variant responsible for the condition. The other methods are simpler and cheaper but less reliable. Knowing your ALDH2 status matters because the deficiency significantly raises cancer risk if you drink alcohol.
What ALDH2 Deficiency Actually Does
When you drink alcohol, your body breaks it down in two steps. First, alcohol is converted into acetaldehyde, a toxic compound and known carcinogen. Then, an enzyme called ALDH2 converts that acetaldehyde into harmless acetate. In people with ALDH2 deficiency, that second step is impaired. Acetaldehyde builds up in the bloodstream instead of being cleared, causing facial flushing, headache, nausea, and rapid heartbeat.
The severity depends on whether you inherited one or two copies of the deficient gene. People with two copies have essentially zero ALDH2 enzyme activity and typically can’t tolerate alcohol at all. People with one copy retain less than 20% of normal enzyme activity. They can often drink, but acetaldehyde still accumulates at dangerous levels. About 45% of Han Chinese carry this variant, and prevalence reaches nearly 50% in Taiwan. The mutation is highly concentrated in East and Southeast Asian populations, including Japan, Korea, Vietnam, and Singapore.
Genetic Testing
A DNA test is the gold standard for diagnosing ALDH2 deficiency. It looks for a specific variant called rs671, a single-letter change in the ALDH2 gene where a G (guanine) is swapped for an A (adenine). This tiny change alters one amino acid in the enzyme’s structure, which is enough to cripple its function.
The test returns one of three results. GG means you have two normal copies and full enzyme activity. AG means you carry one deficient copy (heterozygous), with less than 20% of normal activity. AA means both copies are deficient (homozygous), with nearly zero activity. Both AG and AA individuals are considered ALDH2 deficient.
You can get this test through a healthcare provider who orders targeted genotyping, or through consumer genetic testing services. Several direct-to-consumer DNA kits now include ALDH2 status in their reports. The test typically requires only a saliva sample or cheek swab. If you’re using a consumer kit, check that it specifically covers the rs671 variant, as not all panels include it.
The Ethanol Patch Test
The ethanol patch test is a simple, low-cost screening method that can be done in a clinic. A drop of ethanol is placed on a small gauze pad, which is taped to your inner arm. After about seven minutes, the gauze is removed and the skin underneath is checked for redness, itching, or swelling. If you’re ALDH2 deficient, acetaldehyde accumulates locally in the skin and triggers visible redness at the patch site.
The timing of when redness is assessed matters. Checking immediately after removing the patch catches about 70% of people with inactive ALDH2 (sensitivity of 69.6%) while correctly ruling out about 88% of those without it (specificity of 87.7%). Waiting ten minutes after patch removal improves detection: sensitivity rises to 85.2% with specificity at 85.1%. So if your provider uses this test, the reading taken at ten minutes is more informative than the immediate one.
The patch test is useful as a quick screen, but it can miss roughly 15% of deficient individuals even under the best conditions. Skin tone, recent alcohol exposure, and other variables can affect the result. A negative patch test doesn’t definitively rule out ALDH2 deficiency.
Flushing Questionnaires
Self-report questionnaires ask whether you experience facial flushing after drinking alcohol, how quickly it occurs, and whether it has changed over time. These are the simplest screening tool and require no equipment or medical visit.
Accuracy varies depending on the questionnaire design. A modified version tested in a clinical study achieved 95.1% sensitivity, meaning it caught nearly all deficient individuals, but specificity was only 76.5%, meaning about one in four people flagged as deficient actually had normal ALDH2 function. A different version of the questionnaire showed 78.9% sensitivity and 82.1% specificity. In practical terms, flushing questionnaires are better at ruling the condition in than ruling it out. If you flush reliably after small amounts of alcohol, there’s a strong chance you carry the variant. But some people with the deficiency, particularly those who have developed tolerance over years of drinking, may no longer flush visibly, which makes this method less reliable for regular drinkers.
Breath Testing
A newer approach measures acetaldehyde directly in breath after consuming a very small amount of alcohol. In one validated protocol, participants drink just 100 milliliters of a 0.5% ethanol solution (roughly equivalent to a few sips of very weak beer). Breath samples are then collected in special gas bags and analyzed using gas chromatography. The ratio of breath acetaldehyde to breath ethanol identifies carriers of the deficient gene with 96.4% overall accuracy.
This method bridges the gap between simple screening and full genetic testing. It’s more objective than a flushing questionnaire and more accurate than the patch test, while still being noninvasive. However, it requires specialized equipment and isn’t widely available outside of research settings or certain clinics in East Asia.
Why Testing Matters
ALDH2 deficiency isn’t just an inconvenience that makes your face turn red. It substantially increases the risk of esophageal cancer and other alcohol-related cancers. People with one deficient copy who drink heavily face a 6.5 times higher risk of esophageal cancer compared to those with normal ALDH2. Even light drinking (under 30 grams of alcohol per day, roughly two standard drinks) raises esophageal cancer risk by over 14 times in carriers compared to non-drinking individuals with normal enzyme function.
The risk pattern is counterintuitive in one respect. People with two deficient copies (AA genotype) tend to avoid alcohol altogether because it makes them so sick, which partially protects them. The greater danger falls on people with one copy (AG genotype) who can tolerate drinking despite impaired acetaldehyde clearance. They accumulate the carcinogen regularly without the body’s strongest warning signal forcing them to stop.
Knowing your ALDH2 status gives you concrete information for making decisions about alcohol. If you’re of East or Southeast Asian descent and experience any flushing with alcohol, genetic testing provides a definitive answer. If genetic testing isn’t accessible, an ethanol patch test or a validated flushing questionnaire can give you a reasonable indication, keeping in mind that neither is as conclusive as a DNA result.