Alpha₁-Antitrypsin (AAT) Test

AAT is made in the liver and is the most abundant serum protease inhibitor. It inhibits trypsin and elastin as well as several other proteases. The release of proteolytic enzymes from plasma onto surface organs and into tissue spaces results in tissue damage unless inhibitors are present.

Measurement of AAT aids in the diagnosis of juvenile and adult cirrhosis of the liver. AAT deficiency has been associated with neonatal respiratory distress syndrome, severe protein-losing disorders, and pulmonary emphysema. The test is useful for individuals in whom familial chronic obstructive lung disease is suspected.

• Adults: < 60 years: 78–200 mg/dL or 0.78–2.0 g/L by nephelometry

• >60 years: 115–200 mg/dL or 1.15–2.0 g/L

• Newborns: 145–270 mg/dL or 1.45–2.70 g/L

1. Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions.

2. Label the specimen with the patient’s name, date, and test(s) ordered and place in a biohazard bag for transport to the laboratory.

1. Patients with a serum AAT <70 mg/dL (<0.70 g/L) may have a homozygous deficiency and are at risk for early lung disease. AAT phenotyping should be done to confirm the presence of the homozygous deficiency.

2. If clinically indicated, patients with serum levels <125 mg/dL (<1.25 g/L) should be phenotyped to identify heterozygous individuals. The latter do not appear to be at increased risk for early emphysema.

Pretest Patient Care

1. Explain test purpose and procedure. Follow-up testing, that is, AAT phenotyping, may be necessary if decreased levels are obtained.

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

AAT is an acute-phase reactant, and any inflammatory process will elevate serum AAT levels.