An alpha-1 antitrypsin deficiency genetic test examines the SERPINA1 gene for variants that lower the amount or function of alpha-1 antitrypsin, often shortened to AAT. The test helps explain unexplained emphysema, chronic obstructive pulmonary disease, bronchiectasis, liver disease, or a low AAT blood level. It can also identify relatives who carry a high-risk genotype before organ damage becomes obvious. The most familiar variants are the Z and S alleles, but rare deficiency and “null” variants are important, so limited testing can miss clinically meaningful results. Diagnosis usually combines three kinds of evidence: the serum AAT concentration, protein phenotype or targeted genotyping, and full SERPINA1 sequencing when results do not agree. Lung disease mainly results from too little protective AAT in the airways, while liver disease mainly results from abnormal protein accumulating inside liver cells. Smoking, dust exposure, alcohol, metabolic liver disease, and other factors strongly influence whether a genetically susceptible person becomes ill.
- A low serum AAT level suggests deficiency but should be confirmed because inflammation, pregnancy, and estrogen can raise the level.
- The Pi*ZZ genotype carries the highest common risk for emphysema and AAT-related liver disease, but disease severity varies widely.
- PiMZ and PiSZ results usually confer lower risk than Pi*ZZ, yet smoking and other liver or lung stressors can make the risk clinically important.
- A normal or near-normal AAT level does not exclude a dysfunctional or rare SERPINA1 variant when clinical suspicion is strong.
- Genetic testing does not show whether lung or liver damage is already present; spirometry, imaging, liver tests, and fibrosis assessment answer that question.
- New jaundice, vomiting blood, severe breathlessness, bluish lips, confusion, or coughing blood requires urgent medical care.
Table of Contents
- What SERPINA1 testing detects
- Who should be tested
- AAT blood level, genotype, and phenotype
- Understanding common SERPINA1 results
- Lung risk and follow-up
- Liver risk and follow-up
- Family testing and inheritance
- Next steps after testing
What SERPINA1 testing detects
SERPINA1 provides instructions for making alpha-1 antitrypsin, a protein produced mainly in the liver. The protein travels through the bloodstream to the lungs, where it limits damage from neutrophil elastase and other enzymes released during inflammation. Without enough functional AAT, lung tissue can break down faster, leading to emphysema and airflow obstruction.
The same gene can cause liver disease through a different mechanism. The common Z protein folds abnormally and becomes trapped inside liver cells. This accumulation can trigger inflammation, fibrosis, cirrhosis, and liver cancer risk. In other words, the lungs are injured by a lack of circulating protection, while the liver may be injured by a toxic buildup of abnormal protein.
People inherit one SERPINA1 allele from each parent. Alleles are often described with the protease inhibitor, or “Pi,” naming system:
- M usually represents normal production and function.
- Z causes severe retention of abnormal protein and markedly reduced blood levels.
- S causes a milder reduction in circulating AAT.
- Null variants produce little or no AAT protein and can create severe lung risk, but usually do not cause the same liver protein-accumulation injury as Z variants.
- Dysfunctional variants may produce a measurable protein that does not work normally.
A genetic test may be limited to S and Z genotyping, or it may sequence the entire SERPINA1 coding region and assess deletions or duplications. Targeted S/Z testing identifies many common cases, but it can miss rare alleles. Full sequencing is especially useful when the AAT level, protein phenotype, and targeted genotype do not match.
A result should be described by the exact alleles and, when available, standardized DNA and protein notation. Saying only “alpha-1 carrier” can be misleading because an MZ carrier, an SZ compound heterozygote, and a person with an M/null genotype have different expected risks.
Who should be tested
Current guidance supports testing in several clinical situations because AAT deficiency remains underdiagnosed. Testing is reasonable for adults with chronic obstructive pulmonary disease, emphysema, or persistent airflow obstruction, even when smoking appears to explain the disease. The diagnosis can affect exposure counseling, family screening, and eligibility for specialist therapies.
Testing should also be considered for people with:
- Emphysema at a young age or with little smoking exposure
- Basilar-predominant emphysema on chest imaging
- Unexplained bronchiectasis
- Adult-onset asthma with fixed airflow obstruction
- Necrotizing panniculitis, a painful inflammatory skin disorder
- Granulomatosis with polyangiitis in selected clinical settings
- Unexplained elevated liver enzymes, fibrosis, cirrhosis, or liver cancer
- Neonatal cholestasis or childhood liver disease without another explanation
- A first-degree relative with AAT deficiency or a high-risk SERPINA1 genotype
Testing only people who look “classic” misses many cases. A person with Pi*ZZ can have no lung symptoms into later adulthood, and a person with severe COPD may not have the expected lower-lung distribution. Likewise, liver disease can appear in infancy, childhood, or adulthood.
A family history may be absent because relatives were never tested, died before diagnosis, or had their disease labeled as smoking-related COPD, fatty liver, or cryptogenic cirrhosis. Small families and adoption can also hide inheritance patterns.
For a person with a low AAT blood level, genetic confirmation clarifies whether the reduction is inherited and which relatives are at risk. For a person with a known family variant, targeted testing is usually the simplest approach. A broader clinical genetic diagnostic test may be appropriate when results are discordant or a rare allele is suspected.
Testing should not be used as a stand-alone screening for current organ damage. A genetically high-risk person still needs clinical evaluation to determine whether the lungs or liver are affected.
AAT blood level, genotype, and phenotype
A complete evaluation often uses three complementary tests. Each answers a different question.
| Test | What it shows | Main limitation |
|---|---|---|
| Serum AAT concentration | The amount of AAT circulating in blood at that moment | Inflammation, pregnancy, and estrogen can raise the level and hide deficiency |
| Protein phenotype | The migration pattern of AAT protein variants, often reported as Pi type | May not identify null alleles well and can be affected by transfusion or liver transplant |
| SERPINA1 genotype or sequencing | The inherited DNA variants that explain production or function | Limited panels miss rare variants; some findings remain uncertain |
Laboratories use different units and methods for serum AAT. A frequently cited severe-deficiency threshold is about 11 micromolar, which corresponds roughly to 57 mg/dL by nephelometry, but the conversion depends on the assay. The laboratory’s own reference interval and method must be used. A value slightly above a cutoff does not automatically mean low risk.
AAT is an acute-phase reactant. Infection, inflammation, pregnancy, and estrogen therapy can increase the measured concentration. Measuring C-reactive protein at the same time can help identify an inflammatory state. Testing may need to be repeated after an acute illness.
Discordance deserves investigation. Examples include:
- A very low AAT level with an MM phenotype
- An MZ genotype but a level much lower than expected
- A normal level in someone with a strong family history and severe early emphysema
- A phenotype showing an unusual band not explained by S/Z genotyping
In these situations, full SERPINA1 sequencing and deletion/duplication analysis can identify rare deficiency, null, or dysfunctional alleles. Recent respiratory guidance increasingly supports sequencing as an initial or reflex test when clinical suspicion is high.
Blood transfusion can temporarily alter phenotype results. After liver transplantation, the circulating AAT phenotype reflects the donor liver because the liver makes most of the protein. The recipient’s germline DNA genotype remains unchanged, so genetic testing from blood or another tissue may still identify inherited variants.
Understanding common SERPINA1 results
SERPINA1 results describe a spectrum rather than a simple positive or negative state. Clinical risk depends on both alleles, the measured AAT level, and environmental exposures.
Pi*MM
MM is the usual genotype and generally produces normal AAT levels. It makes classic inherited AAT deficiency unlikely. Rare variants can occasionally be missed if testing looked only for S and Z, so a strongly discordant clinical picture may justify sequencing.
Pi*MZ
MZ carriers have one normal M allele and one Z allele. AAT levels are often moderately reduced. Most never develop severe AAT-related disease, but smoking markedly increases COPD risk. Liver risk is also higher than in MM individuals when other stressors such as metabolic dysfunction, obesity, heavy alcohol use, or viral hepatitis are present.
Pi*MS
MS usually causes little or no clinically important deficiency by itself. It can matter for reproductive counseling because the S allele may combine with a partner’s Z, null, or other deficiency allele in a child.
Pi*SZ
SZ often produces intermediate deficiency. Lung risk is higher than in MZ or MS and rises substantially with smoking. Liver risk exists but is generally lower than in ZZ. Some SZ individuals have AAT levels near or below the severe-deficiency threshold, so the actual concentration and clinical phenotype matter.
Pi*ZZ
ZZ is the most common severe genotype. Circulating AAT is markedly reduced, and the abnormal Z protein accumulates in hepatocytes. Lung and liver outcomes remain variable. Some nonsmokers retain good lung function into older age, while others develop emphysema. Only a subset develops advanced liver disease, but risk increases with age and metabolic or alcohol-related injury.
Null and rare variants
Two null alleles can produce almost no circulating AAT and severe lung susceptibility. Because no abnormal protein is retained, null-null genotypes usually lack the Z-related liver accumulation mechanism. A Z/null combination can create both severe lung deficiency and liver risk from the Z allele.
A variant of uncertain significance should not be treated as a confirmed deficiency allele without supporting biochemical or functional evidence. The laboratory may use serum level, phenotype, family segregation, and experimental studies to clarify it. Reinterpretation is appropriate as new data emerge.
Lung risk and follow-up
The most effective lung protection is complete avoidance of smoking. This includes cigarettes, cigars, vaping products that irritate the airways, and significant secondhand smoke. Smoking accelerates elastin destruction and can move severe lung disease decades earlier.
Occupational exposure also matters. Dust, fumes, combustion products, and aerosolized chemicals can worsen airway inflammation. People with high-risk genotypes should discuss respiratory protection and job exposure with an occupational-health clinician.
Baseline evaluation may include:
- Symptom review for breathlessness, wheeze, cough, sputum, and exercise limitation
- Spirometry before and after a bronchodilator
- Full pulmonary function testing, including diffusing capacity, when indicated
- Chest CT when symptoms or physiology warrant imaging
- Oxygen assessment in advanced disease
Follow-up frequency depends on genotype, symptoms, smoking history, and prior results. Spirometry is often repeated annually in severe deficiency, though clinicians may adjust the interval. A normal initial test does not guarantee lifelong protection.
Treatment for established COPD generally follows standard care, including inhaled bronchodilators, pulmonary rehabilitation, vaccination, exercise, and prompt treatment of exacerbations. Intravenous AAT augmentation therapy may be considered for selected adults with severe deficiency and emphysema. Eligibility varies by country and insurer and usually depends on genotype, serum level, airflow limitation, smoking status, and specialist assessment.
Augmentation increases circulating AAT but does not reverse existing emphysema. It is not used to treat AAT-related liver disease because adding more circulating protein does not remove the abnormal Z protein trapped in liver cells.
Lung transplantation can be considered for advanced disease using standard transplant criteria. After transplantation, the person’s liver still produces the same AAT level, but the new lungs are protected through avoidance of smoking, exposure control, and transplant care.
Liver risk and follow-up
AAT-related liver disease can be silent. Normal symptoms do not exclude fibrosis, and routine liver enzymes may remain normal despite clinically important scarring. Pi*ZZ adults deserve structured liver assessment even when the original diagnosis was made because of lung disease.
Evaluation may include alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, bilirubin, albumin, platelet count, and international normalized ratio. Ultrasound can assess liver texture, spleen size, and portal hypertension. Elastography estimates liver stiffness and is increasingly preferred for noninvasive fibrosis staging.
Recent expert guidance for adult Pi*ZZ disease emphasizes fibrosis assessment rather than relying on enzymes alone. A liver stiffness value around 8 kPa or higher may indicate clinically significant fibrosis, but device, technique, inflammation, congestion, and body habitus affect interpretation. A hepatologist should interpret borderline or elevated results.
Risk reduction includes:
- Avoiding heavy alcohol use; complete abstinence may be advised with fibrosis or cirrhosis
- Maintaining a healthy weight and treating diabetes, high triglycerides, and metabolic liver disease
- Vaccination against hepatitis A and B when not immune
- Reviewing medicines and supplements for liver toxicity
- Avoiding raw shellfish in advanced liver disease because of severe infection risk
People with cirrhosis need standard surveillance for hepatocellular carcinoma, usually liver ultrasound with or without alpha-fetoprotein every six months, and evaluation for portal-hypertension complications. Liver transplantation can cure the hepatic production defect because the donor liver makes normal AAT. It does not reverse established lung damage, so both organs require assessment.
Children with neonatal cholestasis often improve, but a minority progress to significant fibrosis or liver failure. Long-term follow-up remains important even after jaundice resolves.
Family testing and inheritance
AAT deficiency follows an autosomal codominant pattern: both inherited alleles influence the amount and type of protein. Risk for a child depends on both parents’ genotypes.
For example, if one parent is MZ and the other is MM, each child has a 50% chance of being MZ and a 50% chance of being MM. If both parents are MZ, each pregnancy has a 25% chance of ZZ, a 50% chance of MZ, and a 25% chance of MM.
First-degree relatives of a person with severe deficiency should be offered testing. Testing serum AAT alone is less reliable for family screening because levels overlap between genotypes and can rise during inflammation. Genotyping or sequencing identifies the inherited alleles directly.
Testing children can provide immediate health benefits through smoke avoidance, exposure counseling, liver follow-up, and family planning later. Communication should avoid stigmatizing a child as destined for disease. A genotype identifies susceptibility, not a fixed outcome.
Partners may consider testing when one person carries Z, S, null, or another deficiency allele and the couple wants to understand reproductive risk. Prenatal diagnosis and preimplantation genetic testing are technically possible when familial variants are known, but severity is variable and decisions are personal.
Relatives should receive the exact laboratory report. Phrases such as “positive for alpha-1” or “carrier” do not provide enough information for accurate targeted testing.
Next steps after testing
After a result, the clinician should reconcile the genotype with the serum level and phenotype. A high-risk genotype warrants organ-specific baseline testing; an uncertain or discordant result warrants laboratory review rather than guesswork.
Useful questions include:
- Did the test examine only S and Z, or was the full SERPINA1 gene sequenced?
- What was the AAT concentration, unit, assay, and inflammatory status at collection?
- Does the genotype explain the measured protein level?
- Do I need spirometry, full pulmonary function tests, chest CT, liver elastography, or hepatology referral?
- Am I a candidate for augmentation therapy, and what evidence supports it in my case?
- Which relatives should receive targeted testing?
- Should my partner be tested before pregnancy?
- How often should the genetic classification and organ surveillance plan be reviewed?
Keep copies of the DNA report, phenotype, serum level, lung tests, and liver assessments. Results from different laboratories may use different naming systems, so the original documentation helps future clinicians compare them correctly.
A diagnosis can be useful even before symptoms develop. Avoiding smoke and harmful exposures, recognizing liver risk, vaccinating appropriately, and testing relatives can change the course of disease. At the same time, many people with susceptibility alleles never develop severe illness, so follow-up should be proportionate and individualized.
How genotype affects augmentation-therapy discussions
Intravenous AAT augmentation is intended to raise circulating protective protein in selected adults with emphysema caused by severe deficiency. A high-risk SERPINA1 result can establish biological plausibility, but genotype alone is not enough to prescribe treatment. The decision usually requires a severely reduced AAT level, objective airflow obstruction or emphysema, appropriate age and clinical context, and confirmation that ongoing tobacco exposure has been addressed. Local eligibility rules, product access, lung-function range, and payer requirements also differ.
Augmentation replaces circulating protein; it does not remove polymerized Z protein from liver cells. It is therefore not a treatment for AATD-related liver disease and should not be offered solely because liver enzymes, elastography, or imaging are abnormal. Liver management focuses on fibrosis assessment, avoidance of additional injury, metabolic and alcohol risk reduction, vaccination, surveillance when advanced disease is present, and transplantation evaluation for end-stage disease. A person can require hepatology follow-up even when lung function is normal.
The reverse is also true: a person with severe biochemical deficiency and emphysema may be evaluated for augmentation even without clinically significant liver disease. Pulmonary rehabilitation, inhaled therapy when indicated, vaccination, prompt treatment of exacerbations, exercise, and exposure avoidance remain necessary because augmentation is not a substitute for standard COPD care. Lung transplantation may be considered for advanced respiratory failure, while liver transplantation replaces the source of abnormal AAT and can correct the circulating deficiency in recipients with end-stage liver disease.
Rare and null alleles require particular care. A null genotype can produce profound circulating deficiency without the hepatocyte polymer accumulation typical of the Z allele, so lung risk may be high while intrinsic liver risk differs. Conversely, some rare polymerizing variants can threaten both organs. This is why full variant identification, rather than a generic “low AAT” label, can change counseling even when the immediate treatment plan is based on the measured phenotype.
References
- Alpha-1-Antitrypsin Deficiency Targeted Testing and Augmentation Therapy: A Canadian Thoracic Society Meta-Analysis and Clinical Practice Guideline 2025 (Guideline)
- Multi-Society Expert Panel Consensus Guidance on the Diagnosis and Management of Alpha-1 Antitrypsin Deficiency-Associated Liver Disease 2025 (Consensus Guidance)
- Alpha-1 Antitrypsin Deficiency 2023 (GeneReviews)
- Recommendations for the diagnosis and treatment of alpha-1 antitrypsin deficiency 2024 (Guideline)
- Population genetic testing and SERPINA1 sequencing in a large cohort of patients with liver disease 2023
- Alpha-1-Antitrypsin Deficiency 2022 (Review)
Disclaimer
This article is educational and does not replace interpretation by a pulmonologist, hepatologist, genetic counselor, or other qualified clinician. Serum AAT values, genotypes, organ testing, and treatment eligibility must be interpreted together. Severe breathing difficulty, bluish lips, confusion, vomiting blood, black stools, or sudden jaundice requires urgent medical care.
