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Alpha-1 Antitrypsin

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

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.