Alpha-1 antitrypsin, often shortened to A1AT or AAT, is a protective protein made mainly by the liver and released into the bloodstream. Its best-known job is to protect lung tissue from enzymes released during inflammation, especially neutrophil elastase. The A1AT blood test measures how much of this protein is circulating. A low result can point to alpha-1 antitrypsin deficiency, an inherited condition that can raise the risk of emphysema, chronic obstructive pulmonary disease, liver scarring, cirrhosis, and, less commonly, skin inflammation called panniculitis. A1AT testing is different from many routine liver blood tests because it can uncover a genetic reason for lung or liver disease. The number alone is helpful, but it is not always enough. Inflammation can temporarily raise A1AT, and some people with risky gene variants may have levels that look only mildly low or even near normal.
- A1AT is a liver-made protein that protects the lungs from inflammation-related tissue damage.
- Low A1AT can suggest inherited alpha-1 antitrypsin deficiency, especially when results are well below the lab range.
- Many labs list a typical adult reference range near 100–220 mg/dL, but ranges vary by method and laboratory.
- A low or suspicious result is usually followed by A1AT phenotype testing, SERPINA1 genetic testing, or both.
- A normal A1AT level does not always rule out a carrier state because A1AT can rise during inflammation, infection, pregnancy, or estrogen therapy.
Table of Contents
- What the A1AT Blood Test Measures
- When A1AT Testing Is Used
- Normal, Low, and High A1AT Results
- Phenotype, Genotype, and Confirmation
- Liver Disease and A1AT Deficiency
- Lung Risk and A1AT Deficiency
- Factors That Can Change A1AT Levels
- Next Steps After an Abnormal A1AT Test
What the A1AT Blood Test Measures
The A1AT blood test measures the concentration of alpha-1 antitrypsin in serum or plasma. Alpha-1 antitrypsin belongs to a group of proteins called serine protease inhibitors, or serpins. In everyday terms, it acts like a brake on enzymes that can digest tissue if inflammation gets out of balance.
The main enzyme involved in alpha-1 antitrypsin deficiency is neutrophil elastase. Neutrophils are white blood cells that help fight infection and respond to irritation. When they release elastase in the lungs, A1AT helps limit collateral damage to the delicate elastic structure of the air sacs. Without enough working A1AT, elastase can damage alveoli over time. That damage can lead to emphysema, shortness of breath, chronic cough, and airflow obstruction.
A1AT is made mostly in liver cells. In the most common severe form of A1AT deficiency, the abnormal protein is produced but folds incorrectly. Instead of being released efficiently into the bloodstream, much of it gets trapped inside liver cells. This creates two different problems at the same time: the lungs may not receive enough protective A1AT, and the liver may be injured by protein buildup.
The blood level answers one part of the story: “How much A1AT is present?” It does not fully answer: “Which genetic variant is present?” or “How well does this person’s A1AT work?” That is why clinicians often combine the A1AT level with phenotype or genotype testing.
A1AT testing is not the same as routine liver enzyme testing. A liver function test panel can show liver irritation, bile duct patterns, bilirubin changes, and protein production, but it cannot identify A1AT deficiency by itself. A person can have A1AT deficiency with normal liver enzymes, abnormal liver enzymes, lung symptoms, no symptoms, or a family history that prompts testing before disease appears.
When A1AT Testing Is Used
A1AT testing is commonly ordered when lung disease, liver disease, or family history raises suspicion for inherited deficiency. It is also used when a person has COPD or emphysema at a younger age than expected, especially if they never smoked or smoked only lightly.
Many guidelines recommend testing all adults with COPD at least once, because A1AT deficiency can be missed for years. Some people are first treated as if they have asthma, chronic bronchitis, or smoking-related COPD before the genetic cause is recognized. Testing is especially relevant when emphysema affects the lower parts of the lungs or appears out of proportion to smoking history.
A clinician may order an A1AT test for:
- COPD, emphysema, or fixed airflow obstruction, especially before age 45–50
- Unexplained bronchiectasis, which means damaged or widened airways
- Chronic liver enzyme elevation without a clear cause
- Fatty liver, fibrosis, cirrhosis, or portal hypertension that seems unusual for the person’s risk factors
- Newborn or childhood jaundice that lasts longer than expected
- A family history of A1AT deficiency, emphysema, unexplained liver disease, or liver transplant
- Unexplained panniculitis, a painful inflammatory condition of the fat under the skin
- Granulomatosis with polyangiitis or vasculitis-like illness when A1AT deficiency is part of the differential diagnosis
A1AT testing can also be useful when liver tests show a pattern that does not fit the usual causes. For example, if ALT and AST remain mildly elevated and viral hepatitis, alcohol-related injury, medication injury, and metabolic causes have been considered, an A1AT level may be part of a broader workup. Interpreting ALT and AST patterns alongside A1AT results can help separate liver inflammation from an inherited protein-processing problem.
Family testing has a different purpose. If one person has confirmed A1AT deficiency, close relatives may choose testing to learn whether they have severe deficiency, carrier status, or ordinary-risk results. This can affect smoking avoidance, occupational exposure choices, liver follow-up, and reproductive counseling.
Normal, Low, and High A1AT Results
A1AT results are usually reported in mg/dL, g/L, or micromoles per liter. The reference range depends on the laboratory method, so the lab’s own interval should be used first. Many adult lab ranges fall roughly around 100–220 mg/dL, or about 1.0–2.2 g/L. Some laboratories use different cutoffs.
A low A1AT result means the blood contains less alpha-1 antitrypsin than expected. The lower the value, the stronger the concern for clinically important deficiency. Very low levels are more consistent with severe deficiency genotypes such as PiZZ, PiSZ, or rare null variants. Mildly low levels can occur in carriers, some less severe genetic patterns, protein loss, or lab-method differences.
A normal result lowers the chance of severe deficiency, but it does not always exclude a carrier state. A1AT is an acute-phase reactant, meaning the body can make more of it during inflammation. If someone has a respiratory infection, inflammatory disease, recent surgery, pregnancy, or estrogen exposure, the A1AT level may be higher than their baseline.
A high A1AT level usually reflects inflammation or hormone-related changes rather than “too much protection.” High A1AT is not usually the main diagnostic concern. It may appear with infection, inflammatory disorders, pregnancy, estrogen-containing medications, some cancers, or recent tissue injury. A high result can also hide an inherited deficiency if the person’s usual level would otherwise be low.
| Result pattern | Possible meaning | Common follow-up |
|---|---|---|
| Within the lab range | Severe deficiency is less likely, but carrier status is still possible in some settings | Consider phenotype or genotype testing if clinical suspicion or family history is strong |
| Mildly low | Possible carrier state, less severe variant, or non-genetic factor lowering protein level | Repeat when well; check phenotype or SERPINA1 genotype |
| Clearly low | Higher concern for inherited A1AT deficiency | Confirm with phenotype and/or genotype; assess liver and lung health |
| Very low | Possible severe deficiency, especially with lung disease, liver disease, or family history | Specialist evaluation, family testing discussion, lung and liver staging |
| High | Often an inflammatory or hormonal response | Interpret with symptoms, CRP or other inflammation markers, and timing |
The most important mistake is treating the A1AT number as a final diagnosis. The number should be interpreted with symptoms, family history, liver tests, lung tests, and confirmatory genetic or protein-typing results.
Phenotype, Genotype, and Confirmation
A low A1AT level is usually followed by tests that identify the inherited pattern. These tests are often described with terms such as phenotype, genotype, Pi type, or SERPINA1 testing.
The phenotype test looks at the A1AT protein pattern in the blood. The “Pi” label stands for protease inhibitor. A common normal pattern is PiMM. The M variant is the usual form. The S and Z variants are the most common clinically relevant abnormal forms, although many rare variants exist.
Genotype testing looks directly for changes in the SERPINA1 gene. Many panels check for the common S and Z variants. More complete sequencing may be needed if the A1AT level is very low but common-variant testing does not explain the result.
The most common patterns include:
| Pattern | Typical interpretation | General risk pattern |
|---|---|---|
| PiMM | Usual normal pattern | Typical A1AT level and ordinary inherited risk |
| PiMS | Carrier of one S variant | Usually enough A1AT for lung protection |
| PiMZ | Carrier of one Z variant | Often moderately lower A1AT; risk rises with smoking, liver cofactors, and family context |
| PiSS | Two S variants | Usually mild to moderate reduction; severe disease is less common than with Z patterns |
| PiSZ | One S and one Z variant | Intermediate to sometimes significant lung risk, especially with smoking |
| PiZZ | Most common severe deficiency pattern | Higher risk of emphysema and liver disease |
| Null variants | Little or no A1AT production from the affected gene | High lung risk when severe; liver buildup may be less prominent with pure null variants |
A1AT inheritance is often described as codominant. This means both copies of the gene can influence the amount and type of protein made. A person with PiMZ usually has less A1AT than a person with PiMM, but more than a person with PiZZ. The pattern is not as simple as “carrier means no risk.” Many carriers stay healthy, but PiMZ status can become more relevant when combined with smoking, heavy alcohol use, metabolic syndrome, obesity, viral hepatitis, or another liver condition.
Confirmation matters because the result affects relatives. If a person has PiZZ, PiSZ, a rare severe variant, or a null variant, first-degree relatives may benefit from targeted testing. Testing children raises additional counseling issues, especially when the child is healthy, so families should discuss timing and implications with a clinician or genetic counselor.
Liver Disease and A1AT Deficiency
A1AT deficiency can affect the liver because abnormal A1AT may accumulate inside liver cells. This is most strongly associated with the Z variant, especially PiZZ. The trapped protein can irritate liver cells, trigger inflammation, and contribute to fibrosis, which means scarring.
Liver disease from A1AT deficiency can appear at different ages. Some infants develop prolonged jaundice or cholestasis. Some children improve after infancy and remain stable. Some adults are diagnosed only after years of mild liver enzyme elevation, fatty liver, fibrosis, cirrhosis, or an evaluation for abnormal imaging.
The liver risk is not fully predicted by the A1AT blood level. Two people with the same PiZZ pattern can have different outcomes. Other factors can increase strain on the liver, including alcohol, obesity, insulin resistance, viral hepatitis, and certain medications or toxins. A person with A1AT deficiency may need the same careful review used for other chronic liver conditions: alcohol intake, metabolic risk, medication exposures, viral hepatitis screening, autoimmune markers when appropriate, iron studies, and imaging.
Routine blood tests can miss early fibrosis. ALT, AST, ALP, GGT, bilirubin, albumin, platelet count, and INR provide useful clues, but they do not measure liver scarring directly. A clinician may combine blood tests with ultrasound, elastography, fibrosis scores, or specialist evaluation. When scarring is a concern, comparing FIB-4 and APRI liver fibrosis scores may help decide whether more direct assessment is needed.
A1AT-related liver disease can show different blood test patterns:
- Mild ALT or AST elevation
- A cholestatic pattern with higher ALP or GGT in some cases
- Low albumin, high INR, or low platelets when cirrhosis is advanced
- Normal enzymes even when some fibrosis is present
Albumin and INR deserve special attention in advanced disease because they reflect the liver’s ability to make proteins involved in fluid balance and clotting. If cirrhosis is suspected, albumin and INR patterns can provide more information than liver enzymes alone.
There is no standard medication that removes Z-A1AT buildup from the liver in routine clinical care. Treatment focuses on monitoring, reducing liver stress, managing complications, and evaluating for transplant if liver failure or decompensated cirrhosis develops. Liver transplant can replace the liver source of abnormal A1AT production, but it is reserved for severe cases.
Lung Risk and A1AT Deficiency
A1AT deficiency raises lung risk because the lungs need A1AT to counter enzymes released during inflammation. When A1AT is severely low or poorly functioning, lung tissue becomes more vulnerable to injury. Over time, this can cause emphysema, COPD, reduced exercise capacity, chronic cough, wheezing, and shortness of breath.
Smoking is the strongest avoidable risk factor. Cigarette smoke increases inflammation and can chemically inactivate A1AT. This means a person with severe deficiency who smokes faces both lower protection and higher inflammatory injury. Vaping, occupational dust, fumes, biomass smoke, and repeated respiratory infections may also add stress, although cigarette smoking remains the clearest major risk.
A1AT-related emphysema often affects the lower lung zones more than typical smoking-related emphysema, though patterns vary. Symptoms can overlap with asthma or chronic bronchitis. Some people notice breathlessness during hills, stairs, sports, or heavy work years before they receive a diagnosis.
Lung evaluation after confirmed deficiency may include:
- Spirometry to measure airflow obstruction
- Bronchodilator testing to see whether airflow improves after medication
- Diffusing capacity testing, often called DLCO, to assess gas transfer
- Chest CT when emphysema, bronchiectasis, or other structural disease is suspected
- Oxygen testing during rest, sleep, or exertion when symptoms suggest low oxygen
- Review of exposures at home and work
Treatment depends on the person’s lung findings, symptoms, genotype, and A1AT level. Standard COPD care may include inhalers, pulmonary rehabilitation, exercise planning, vaccination, prompt treatment of infections, and oxygen when medically needed. Selected people with severe deficiency and established emphysema may be considered for intravenous A1AT augmentation therapy. This therapy aims to raise blood and lung A1AT levels; it is not used to treat A1AT-related liver disease.
A normal breathing test does not mean A1AT deficiency can be ignored. It may mean there is an opportunity to protect lung function before damage appears. Avoiding smoke, reducing dust and fume exposure, staying current with vaccinations, and treating respiratory infections promptly can make a major difference over time.
Factors That Can Change A1AT Levels
A1AT is an acute-phase protein. The liver makes more of it during inflammation, infection, injury, and some hormone-related states. Because of this, a single result can be misleading when the person is not at their usual baseline.
A1AT may rise with:
- Recent infection, including respiratory infections
- Active inflammatory or autoimmune disease
- Recent surgery, trauma, or tissue injury
- Pregnancy
- Estrogen-containing medication
- Some cancers or chronic inflammatory states
A1AT may be lower because of inherited deficiency, but non-genetic factors can also influence protein levels. Severe protein loss through the kidneys or gut, advanced liver failure with reduced protein production, and some rare nutritional or inflammatory states may affect interpretation. These situations do not usually create the classic PiZZ pattern, but they can complicate the meaning of a low number.
Timing matters. If A1AT is checked during pneumonia, a COPD flare, a major inflammatory illness, or pregnancy, the result may look more reassuring than it should. A clinician may repeat the test when the person is well and may order C-reactive protein, often called CRP, to see whether inflammation was present at the time of sampling.
The lab method also matters. Different assays can produce slightly different values. Older literature may use protective thresholds expressed in micromoles per liter, while many clinical labs report mg/dL. The often-cited severe-deficiency threshold of 11 micromoles per liter is not identical across every assay conversion. For patients, the safest approach is to read the result against the lab’s own reference interval and ask whether confirmatory phenotype or genotype testing is needed.
Do not use A1AT level to monitor ordinary liver inflammation the way ALT, AST, ALP, GGT, or bilirubin are used. If the concern is liver injury, the A1AT test helps identify a cause; it does not replace follow-up with liver enzymes, bilirubin, imaging, fibrosis assessment, or clinical evaluation. In some cases, pairing A1AT results with GGT and ALT patterns helps clinicians see whether other liver stressors are present.
Next Steps After an Abnormal A1AT Test
An abnormal A1AT result should be handled in stages. The first stage is confirming whether the result reflects inherited deficiency. The second is checking whether the lungs or liver have already been affected. The third is prevention, monitoring, and family counseling.
For a low result, common next steps include repeating the A1AT level if the timing was unusual, checking phenotype or SERPINA1 genotype, and reviewing family history. If the level is clearly low, confirmation should not be delayed only because the person feels well. Many people with A1AT deficiency have no symptoms for years.
For confirmed deficiency, lung follow-up usually includes baseline spirometry and exposure counseling. A person who smokes should receive direct support to stop, not just general advice. Avoiding secondhand smoke, vaping, dusty workplaces without protection, and repeated high-irritant exposures is especially important.
Liver follow-up may include a hepatic panel, platelet count, INR, albumin, ultrasound, elastography, and fibrosis risk assessment. People with cirrhosis need standard cirrhosis care, which may include screening for varices and liver cancer. The exact plan depends on age, genotype, symptoms, alcohol use, metabolic health, and previous results.
Family members may need targeted testing rather than only a basic A1AT level. A relative can carry a clinically relevant variant even if their level is not dramatically low. Genetic counseling can help families understand carrier status, reproductive implications, and whether testing children is appropriate.
Medical care should also include routine prevention:
- Avoid smoking and vaping, and reduce secondhand smoke exposure
- Stay current with influenza, COVID-19, pneumococcal, and other recommended vaccines
- Discuss hepatitis A and hepatitis B vaccination if not immune
- Limit alcohol, especially with confirmed liver involvement
- Manage weight, diabetes risk, cholesterol, and fatty liver risk factors
- Review medications and supplements that may affect the liver
- Seek care promptly for worsening shortness of breath, jaundice, abdominal swelling, vomiting blood, black stools, confusion, or severe right upper abdominal pain
A1AT deficiency is not defined by one blood number alone. A low level starts the investigation, but the most useful interpretation combines the protein level, inherited variant, lung function, liver health, and the person’s exposures. When those pieces are put together, the result can guide prevention long before advanced lung or liver disease develops.
References
- Alpha1-Antitrypsin Deficiency 2020 (Review)
- Alpha-1 Antitrypsin Deficiency 2023 (GeneReviews)
- The Diagnosis and Management of Alpha-1 Antitrypsin Deficiency in the Adult 2016 (Guideline)
- Liver fibrosis and metabolic alterations in adults with alpha-1-antitrypsin deficiency caused by the Pi*ZZ mutation 2019 (Cohort Study)
- Intravenous alpha-1 antitrypsin augmentation therapy for treating patients with alpha-1 antitrypsin deficiency and lung disease 2016 (Systematic Review)
Disclaimer
A1AT results should be interpreted by a qualified healthcare professional, especially when lung disease, liver disease, pregnancy, inflammation, or family history is involved. This information is for education and cannot diagnose alpha-1 antitrypsin deficiency or replace individualized medical advice. Seek urgent care for severe breathing trouble, coughing blood, confusion, fainting, black stools, vomiting blood, or rapidly worsening jaundice.
