URL of this page: https://medlineplus.gov/lab-tests/alpha-1-antitrypsin-test/

Alpha-1 Antitrypsin Test

What is an alpha-1 antitrypsin (AAT) test?

This test measures the amount of alpha-1 antitrypsin (AAT) in the blood. AAT is a protein that is made in the liver. It helps protect your lungs from damage and diseases, such as emphysema and chronic obstructive pulmonary disease (COPD).

AAT is made by certain genes in your body. Genes are the basic units of heredity passed down from your parents. They carry information that determines your unique traits, such as height and eye color. Everyone inherits two copies of the gene that makes AAT, one from their father and one from their mother. If there is a mutation (change) in one or both copies of this gene, your body will make less AAT or AAT that doesn't work as well as it should.

  • If you have two mutated copies of the gene, it means you have a condition called AAT deficiency. People with this disorder have a higher risk of getting lung disease or liver damage before the age of 45.
  • If you have one mutated AAT gene, you may have lower than normal amounts of AAT, but mild or no symptoms of disease. People with one mutated gene are carriers of AAT deficiency. This means you don't have the condition, but you could pass the mutated gene on to your children.

An AAT test can help show if you have the genetic mutation that puts you at risk for disease.

Other names: A1AT, AAT, alpha-1-antiprotease deficiency, α1-antitrypsin

What is it used for?

An AAT test is most often used to help diagnose AAT deficiency in people who develop lung disease at an early age (45 years or younger) and do not have other risk factors such as smoking.

The test may also be used to diagnose a rare form of liver disease in infants.

Why do I need an AAT test?

You may need an AAT test if you are under the age of 45, are not a smoker, and have symptoms of lung disease, including:

  • Wheezing
  • Shortness of breath
  • Chronic cough
  • Faster than normal heartbeat when you stand up
  • Vision problems
  • Asthma that doesn't respond well to treatment

You may also get this test if you have a family history of AAT deficiency.

AAT deficiency in babies often affects the liver. So your baby may need an AAT test if his or her health care provider finds signs of liver disease. These include:

What happens during an AAT test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for an AAT test.

Are there any risks to the test?

There is very little risk to a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If your results show a lower than normal amount of AAT, it probably means you have one or two mutated AAT genes. The lower the level, the more likely it is you have two mutated genes and AAT deficiency.

If you are diagnosed with AAT deficiency, you can take steps to reduce your risk of disease. These include:

  • Not smoking. If you are a smoker, quit smoking. If you don't smoke, don't start. Smoking is the leading risk factor for life-threatening lung disease in people with AAT deficiency.
  • Following a healthy diet
  • Getting regular exercise
  • Seeing your health care provider regularly
  • Taking medicines as prescribed by your provider

If you have questions about your results, talk to your health care provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about an AAT test?

Before agreeing to be tested, it may help to speak with a genetic counselor. A genetic counselor is a specially trained professional in genetics and genetic testing. A counselor can help you understand the risks and benefits of testing. If you are tested, a counselor can help you understand the results and provide information on the condition, including your risk of passing the disease on to your children.


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The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.