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Home :: Alpha1 - Antitrypsin

Alpha1 - Antitrypsin

A protein produced by the liver, alpha1 - antitrypsin (also known as AAT or -AT) is believed to inhibit the release of protease into body fluids by dying cells and is a major component of alpha1 globulin. AAT is measured using radioimmunoassay or isoelectric focusing. Congenital absence or deficiency of AAT has been linked to high susceptibility to emphysema.


  • To screen for high-risk emphysema patients.
  • As a nonspecific method of detecting inflammation, severe infection, and necrosis.
  • To test for congenital AAT deficiency.

Patient preparation

  • Explain to the patient that this test is used to diagnose respiratory or liver disease as well as inflammation, infection, or necrosis.
  • Tell the patient to avoid smoking because irritants in tobacco stimulate leukocytes in the lungs to release protease.
  • Tell the patient to avoid oral contra­ ceptives and steroids for 24 hours before the test.
  • Tell the patient to fast for at least 8 hours before the test.
  • Tell the patient who will perform the venipuncture and when.
  • Explain that he may experience slight discomfort from the needle puncture and the tourniquet but that collecting the sample usually takes less than 3 minutes

Procedure and posttest care

  • Perform a venipuncture, and collect the sample in a 7-ml red-top tube.

  • Handle the sample gently to avoid hemolysis.
  • Send the sample to the laboratory promptly.
  • If clinically indicated, patients with AAT levels lower than 125 mg/dl should be phenotyped to confirm homozygous and heterozygous deficiencies. (Heterozygous patients don't seem to be at increased risk for early emphysema.)
Reference values
AAT levels vary by age, but the normal range is 110 to 200 mg/dl.
Abnormal findings

Decreased AAT levels may occur in early-onset emphysema and cirrhosis, nephrotic syndrome, malnutrition, con­genital alpha1 -globulin deficiency and, transiently, in the neonate.

Increased AAT levels can occur in chronic inflammatory disorders, necrosis, pregnancy, acute pulmonary infections, hyaline membrane disease in infants, hepatitis, systemic lupus erythematosus, and rheumatoid arthritis.

Interfering factors

  • Oral contraceptives and steroids (possible false-high)
  • Failure to fast for 8 hours before the test (possible false-high)
  • Smoking

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