When is a functional assay of alpha1-antiprotease indicated in the workup of alpha1-antitrypsin deficiency (AATD)?

Updated: Sep 11, 2020
  • Author: Dora E Izaguirre Anariba, MD, MPH; Chief Editor: John J Oppenheimer, MD  more...
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Answer

In rare circumstances, a third test is used to evaluate a patient with clinical features that are highly suggestive of alpha1-antitrypsin deficiency but whose serum levels are within the reference range.

Specialized laboratories can perform a functional assay of alpha1 antiprotease, which measures the ability of the patient's serum to inhibit human leukocyte elastase. Such a defect is extremely rare.

Diagnosis at a molecular level (ie, genotyping) uses DNA extracted from circulating mononuclear blood cells. This genotyping is accomplished using DNA amplification techniques with melt-curve analysis. [9] Greene et al. established a reference compendium of known AAT phenotypes that can be used as a resource for interpreting AAT phenotypes. Test kits capable of detecting S and Z alleles on samples from mouth swabs have made genetic testing easier. The presence of rare null alleles can be inferred by genotyping, because null alleles do not produce protein that can be identified by a band of isoelectric focusing field. These tests will, however, miss the rare null alleles.

Evaluate hepatic function in patients with low or borderline levels of alpha1-antitrypsin. Measure serum transaminases, bilirubin, albumin, and routine clotting function (activated partial thromboplastin time and international normalized ratio).


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