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Alpha-1 Antitrypsin

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Also known as: Alpha1-antitrypsin; A1AT; AAT
Formal name: Alpha1 Antitrypsin; α1-antitrypsin

At a Glance

Why Get Tested?

To help diagnose the cause of early onset emphysema and/or liver dysfunction; to establish the risk of emphysema and/or liver disease due to alpha-1 antitrypsin deficiency and determine the likelihood that children might inherit the risk

When to Get Tested?

When your infant or young child show signs of liver disease; when you develop emphysema before age 40; when you have a close relative with alpha-1 antitrypsin deficiency

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

Alpha-1 antitrypsin (AAT) is a protein in the blood that protects the lungs from damage caused by activated enzymes. This test measures the level of AAT in blood. Related tests can determine which of the abnormal forms of AAT a person has inherited.

AAT helps to inactivate several enzymes, the most important of which is elastase. Elastase is an enzyme produced by white blood cells called neutrophils and is part of the body's normal response to injury and inflammation. Elastase breaks down proteins so that they can be removed and recycled by the body. If its action is not regulated by AAT, elastase will also begin to break down and damage lung tissue.

Each individual inherits two copies of the gene that codes for AAT. It is called the protease inhibitor (SERPINA1) gene. This gene is co-dominant, which means that each SERPINA1 gene copy is responsible for producing half of the body's AAT. If there is a change or mutation in one or both of the gene copies, then less AAT and/or AAT with reduced function is produced.  When AAT production drops below 30% of normal, the affected person will experience a disorder called alpha-1 antitrypsin deficiency. People with this disorder are at a considerable risk of developing emphysema, a progressive lung disease, in early adulthood. If they smoke or are exposed to occupational dust or fumes, the lung damage tends to occur sooner and be more severe.

Certain types of dysfunctional AAT accumulate in the liver cells, where it is produced. As AAT builds up in these cells, it forms abnormal protein chains and begins to destroy the cells and damage the liver. About 10% of newborns with AAT deficiency have liver damage and are jaundiced. In severe cases, these infants may require a liver transplant to survive. AAT deficiency is currently the most common genetic cause of liver disease in the pediatric population. About 15% of adults with AAT deficiency will develop cirrhosis due to the scarring caused by liver damage and some have a higher risk of developing liver cancer (hepatocellular carcinoma).

The amount and function of the AAT depends on the gene mutation that is inherited. While there are more than 75 different alleles in the SERPINA1 gene, only a few are common. Most people in the U.S., about 90%, have two copies of the normal "wild type" M gene (MM). The most common abnormal genes are labeled S and Z.

Types of AAT Tests
Different types of tests can be used to evaluate an individual:

  • Alpha-1 Antitrypsin measures the blood level of AAT.
  • Alpha-1 Antitrypsin phenotype determines the different types of AAT protein produced.
  • Alpha-1 Antitrypsin DNA testing is genetic testing that can be done to identify which gene mutations (SERPINA1 gene alleles) are present. Only the normal M allele and the most common mutations (S and Z) are usually evaluated.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

(Updated 2012 September 17). Alpha1-Antitrypsin Deficiency. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/295686-overview through http://emedicine.medscape.com. Accessed May 2013.

Dugdale, D. (Updated 2013 March 22). Alpha-1 antitrypsin test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003715.htm. Accessed May 2013.

Grenache, D. et. al. (Updated 2013 March). Alpha-1-Antitrypsin Deficiency – AAT. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/AAT.html?client_ID=LTD through http://www.arupconsult.com. Accessed May 2013.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 40-41.

Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 234-235.

(February 2003) American Thoracic Society/European Respiratory Society Statement: Standards for the Diagnosis and Management of Individuals with Alpha-1 Antitrypsin Deficiency. PDF available for download at http://www.thoracic.org/statements/resources/respiratory-disease-adults/alpha1.pdf through http://www.thoracic.org. Accessed May 2013.

(2006) American Thoracic Society. Patient Information series: What is alpha-1-antitrypsin deficiency? PDF available for download at http://patients.thoracic.org/information-series/en/resources/what-is-alpha-1-antitrypsin-deficiency.pdf through http://patients.thoracic.org. Accessed May 2013.

(February 2011) American Lung Association. Chronic Obstructive Pulmonary Disease Factsheet: Alpha1 antitrypsin deficiency-related (AAT) emphysema. Available online at http://www.lung.org/lung-disease/copd/resources/facts-figures/COPD-Fact-Sheet.html through http://www.lung.org. Accessed May 2013.

(January 2013) Genetics Home Reference. Alpha-1 antitrypsin deficiency. Available online at http://ghr.nlm.nih.gov/condition/alpha-1-antitrypsin-deficiency through http://ghr.nlm.nih.gov. Accessed May 2013.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Barclay, L. and Lie, D. (2003 October 10). New Guidelines for Alpha-1 Antitrypsin Deficiency. Medscape Medical News [On-line News and CME]. Available online at http://www.medscape.com/viewarticle/462776 through http://www.medscape.com.

Huskey, R., Maintained (1998 November 10, Updated). Alpha-1 Antitrypsin Deficiency. From Principles of Medical Genetics by Gelehrter and Collins, 1990 (Williams & Wilkins). Available online at http://www.people.virginia.edu/~rjh9u/antitryp.html through http://www.people.virginia.edu.

Maxton, D. (2000 August 21). Alpha-1 antitrypsin deficiency. Netdoctor.co.uk [On-line information]. Available online at http://www.netdoctor.co.uk/diseases/facts/alpha1def.htm through http://www.netdoctor.co.uk.

Shaffer, E. Alpha1-Antitrypsin Deficiency. The Merck Manual – Second Home Edition [On-line information]. Available online at http://www.merck.com/pubs/mmanual_home2/sec10/ch136/ch136f.htm through http://www.merck.com.

Alpha-1 Related Emphysema. American Lung Association [On-line information]. Available online at http://www.lungusa.org/diseases/luna1ad.html through http://www.lungusa.org.

University of Utah (2003). Alpha-1-antitrypsin. Genetic Testing of Newborn Infants, Genetic Science Learning Center [On-line information]. Available online at http://gslc.genetics.utah.edu/units/newborn/infosheets/alpha.cfm through http://gslc.genetics.utah.edu.

Alpha-1 Antitrypsin Deficiency. Children’s Liver Disease Foundation [On-line information]. Available online at http://www.childliverdisease.org/aatd.html through http://www.childliverdisease.org.

Alpha-1 Antitrypsin Deficiency (A-1ATD). MedicineNet.com [On-line information]. Available online at http://www.medicinenet.com/Alpha_1_Antitrypsin_Deficiency/article.htm through http://www.medicinenet.com.

Alpha-1-Antitrypsin and Alpha-1-Antitrypsin Phenotype. ARUP's Guide to Clinical Laboratory Testing [On-line information]. Available online at http://www.aruplab.com/guides/clt/tests/clt_al38.jsp#1141235 through http://www.aruplab.com.

Kaufman, D. (2003 May 7). Alpha-1 Antitrypsin Deficiency. MEDLINEplus Health Information, Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000120.htm.

Martell, B. (2003 May 12). Alpha-1 antitrypsin. MEDLINEplus Health Information, Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003715.htm.

Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 45-46.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Pp 198-199.

Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 138-143.

Fairman P, and Malhotra R. (2008 October 29, Updated). Alpha1-Antitrypsin Deficiency. eMedicine [On-line information]. Available online at http://www.emedicine.com/med/TOPIC108.HTM through http://www.emedicine.com. Accessed March 2009.

Ohar, J. (2008 January 15). New Data on Chronic Obstructive Pulmonary Disease CME/CE. Medscape from CHEST 2007: Pulmonary Disease [On-line information]. Available online at http://www.medscape.com/viewarticle/568542 through http://www.medscape.com. Accessed March 2009.

(2007 November). What Is Alpha-1 Antitrypsin Deficiency? National Heart, Lung, and Blood Institute [On-line information]. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/aat/aat_whatis.html through http://www.nhlbi.nih.gov. Accessed March 2009.

(2007 September 28, Updated). Alpha-1 Antitrypsin Deficiency. American Liver Foundation [On-line information]. Available online at http://www.liverfoundation.org/education/info/alphaone/ through http://www.liverfoundation.org. Accessed March 2009.

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