Alpha-1 Antitrypsin (AAT) Testing: Normal & Low

Alpha-1 antitrypsin (AAT) is a protein in the blood that protects the lungs from damage caused by activated enzymes. 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.

This test measures the level of AAT in the blood to help diagnose the cause of early onset emphysema and/or liver dysfunction, establish the risk of emphysema and/or liver disease due to AAT deficiency and determine the likelihood that children might inherit the risk.

Reference Range

100 – 190 mg/dL


Low alpha-1-antitrypsin levels may result from liver disease, and AAT proteotyping should be done to confirm AAT deficiency disease.

  • It is thought that levels less than 57 mg/dL predispose to accelerated lung damage.

  • Patients with serum levels less than 70 mg/dL may have a homozygous deficiency and are at risk for early lung disease. Alpha-1-antitrypsin proteotyping should be done to confirm the presence of homozygous deficiency alleles.

  • If clinically indicated, patients with serum levels less than 125 mg/dL should be proteotyped in order to identify heterozygous individuals. Heterozygotes do not appear to be at increased risk for early emphysema.

Keywords: Alpha-1 antitrypsin; AAT.

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