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.
Use
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
Interpretation
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
Limitations
Phenotypic studies are recommended to confirm a suspected hereditary deficiency.
False-positive results can occur if rheumatoid factor present.