Alpha1-Antitrypsin (AAT, Alpha-1 Trypsin Inhibitor, Alpha-1 Proteinase Inhibitor)


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Subject: Alpha1-Antitrypsin (AAT, Alpha-1 Trypsin Inhibitor, Alpha-1 Proteinase Inhibitor)

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  • AAT is a member of the serpin family of protease inhibitors, produced mostly in the liver. It protects the lungs from damage caused by the proteolytic enzyme, neutrophil elastase. The normal AAT allele is the M allele. Over 100 allelic variants have been described, of which the most common severely deficient variants are the S and Z alleles. It is normally the major constituent of the alpha-1 band on routine serum electrophoresis. AAT deficiency is severely underrecognized, with long intervals between the first symptom and diagnosis. Clinical manifestations of severe deficiency of AAT typically involve the lung (e.g., early-onset emphysema with a basilar predominant pattern on imaging), the liver (e.g., cirrhosis), and, rarely, the skin (e.g., panniculitis).

  • Normal range: 88–174 mg/dL.


  • Workup of individuals with suspected disorders such as familial chronic obstructive lung disease, emphysema, asthma, bronchiectasis

  • Diagnosis of AAT deficiency

  • Diagnosis of juvenile and adult cirrhosis of the liver


Increased In

  • Inflammation (acute-phase reacting protein)

  • Infection, tissue injury or necrosis, rheumatic disease, and some malignancies

  • Estrogen administration (oral contraceptives, pregnancy, especially third semester)

Decreased In

  • Deficiency states (hereditary)

  • Hepatic disease (hepatitis, cholestasis, cirrhosis, or hepatic cancer)

  • Pulmonary emphysema, COPD


  • Phenotypic studies are recommended to confirm a suspected hereditary deficiency.

  • False-positive results can occur if rheumatoid factor present.