An alpha-1 antitrypsin (AAT) test measures a protective protein in your blood or checks your genes for changes that reduce how much of that protein your body makes. The test is primarily used to diagnose alpha-1 antitrypsin deficiency, a genetic condition that raises your risk of lung and liver disease. Normal levels in adults fall between 150 and 350 mg/dL.
What Alpha-1 Antitrypsin Does in Your Body
Alpha-1 antitrypsin is a protein made by your liver and released into your bloodstream. Its main job is to protect your lungs from damage caused by your own immune system. Every time your body fights off an infection or reacts to an irritant like cigarette smoke, white blood cells release enzymes that break down damaged tissue. That cleanup process is normal, but those same enzymes can also destroy healthy lung tissue if nothing keeps them in check. AAT acts as the brake, neutralizing those enzymes before they go too far.
When your body doesn’t produce enough AAT, or produces a version that doesn’t work properly, those enzymes chew through the tiny air sacs in your lungs unopposed. Over time this destroys lung structure and leads to emphysema and COPD. The deficiency also affects the liver directly: abnormal AAT protein can build up inside liver cells rather than being released into the bloodstream, gradually causing scarring and cirrhosis.
Three Types of AAT Tests
There isn’t just one AAT test. Depending on what your provider needs to know, you may get one or a combination of these:
- Blood level test: A standard blood draw that measures how much AAT protein is circulating in your blood. This is usually the first step. A result below the normal range of 150 to 350 mg/dL suggests deficiency, but a single low reading isn’t the full picture.
- Genotype test: Uses a blood sample or cheek swab to look at your DNA for the most common gene changes that cause AAT deficiency. This tells you which variant genes you carry and whether you could pass them to your children.
- Phenotype test: Examines the AAT protein itself to identify whether it has structural changes that prevent it from working normally. This helps distinguish between different forms of the deficiency.
No fasting or special preparation is needed for any of these tests. The blood draw takes a few minutes, and a cheek swab for genetic testing is painless.
Why Your Provider Ordered This Test
International guidelines, including those from the World Health Organization and the Global Initiative for Chronic Obstructive Lung Disease (GOLD), recommend AAT testing at least once for every person diagnosed with COPD, regardless of age, ethnicity, or disease severity. It’s also recommended for adults with asthma that doesn’t respond well to standard treatment, especially if lung function tests show airflow obstruction that won’t fully reverse.
Beyond COPD and asthma, your provider may order the test if you have:
- Emphysema, particularly if you’re under 45 or have never smoked
- Repeated respiratory infections like bronchitis
- Chronic liver disease with no clear cause
- Unexplained bronchiectasis (damaged, widened airways)
- Panniculitis, a skin condition causing painful hardened lumps
- A first-degree relative with known AAT deficiency
- A family history of emphysema, liver disease, or cirrhosis without an obvious explanation
In newborns and infants, the test is ordered when a baby shows signs of liver trouble, most commonly prolonged jaundice that appears in the first two months of life. Babies with AAT deficiency may also have poor weight gain, an enlarged liver or spleen, easy bruising, or abdominal swelling. Lung problems from AAT deficiency typically don’t appear until after age 30, so testing in children is almost always prompted by liver symptoms.
What Your Results Mean
A result within the 150 to 350 mg/dL range generally means your AAT levels are normal and deficiency is unlikely. Results below that range suggest your body isn’t producing enough of the protein, or is producing a form that doesn’t enter the bloodstream properly.
One important caveat: AAT is what’s known as an acute-phase protein. Your body ramps up production during infection, injury, or inflammation, sometimes to four to six times normal levels, and those elevated levels can persist for over a week. The third trimester of pregnancy and advanced age also raise AAT levels. This means a blood level test taken while you’re sick, pregnant, or dealing with significant inflammation could mask a true deficiency by pushing a low result into the normal range. If your provider suspects the timing affected your result, they may repeat the test later or go straight to genetic testing, which isn’t influenced by inflammation.
A higher-than-normal result on a blood level test, on its own, is not typically a concern. It usually reflects your body’s response to inflammation or infection rather than a separate disease.
What Happens After a Low Result
If your blood level comes back low, the next step is usually genotype or phenotype testing to identify which genetic variants you carry. AAT deficiency is inherited, and you receive one copy of the gene from each parent. The normal version is called M, so a person with two normal copies is MM. The most common variants linked to deficiency are called S and Z. Someone with two Z copies (ZZ) has the most severe form and typically produces only about 10 to 15 percent of the normal amount of AAT protein.
Carriers who have one normal copy and one abnormal copy (MZ or MS) often have mildly reduced levels. They usually don’t develop serious disease on their own, but their status matters for family planning since they can pass the variant to their children.
Once the genetic picture is clear, follow-up typically involves lung function testing to check for early signs of emphysema and liver function tests to look for scarring. For people with confirmed severe deficiency and lung disease, treatment can include infusions of AAT protein from donor blood to restore protective levels in the lungs. Avoiding smoking is critical, since tobacco smoke dramatically accelerates lung damage in people who lack this protein. Family members, especially siblings, are often encouraged to get tested as well since they have a significant chance of carrying the same genetic variants.
AAT Deficiency in Children
In adults, AAT deficiency primarily damages the lungs. In infants and young children, the liver bears the brunt. Babies with the condition often develop jaundice that lingers beyond the first few weeks of life, caused by impaired bile flow from the liver. Some infants develop more serious complications including poor nutrient absorption, failure to thrive, an enlarged liver, and in rare cases, significant liver scarring. Not every child with AAT deficiency develops liver problems, but unexplained jaundice, abnormal liver enzyme levels, or an enlarged liver in a child should prompt testing. Early identification allows closer monitoring and earlier intervention if liver disease progresses.