A new assay format that is able to accurately measure the level of functionally active alpha-1 antitrypsin (AAT) was reported, according to a new study published in the Journal of Pharmaceutical and Biomedical Analysis.

“The data obtained demonstrated the [elastase complex formation immunosorbent assay] as an accurate, precise, selective, and very sensitive method for AAT activity measurement at low levels previously inaccessible for direct measurement,” the authors said.

Measuring the activity of functional AAT is crucial for the refinement of AAT augmentation therapy, a treatment approach that consists of infusing purified pooled human plasma AAT into the body of patients with AAT deficiency (AATD).

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The aim of AAT augmentation therapy is to raise the concentration of AAT in the serum above the protective threshold to prevent alveolar destruction by neutrophil elastase.

The current tests available to measure levels of functionally active AAT rely on chromogenic elastase inhibition, which does not allow the detection of less than 10 µg per mL of functionally active AAT.

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Elastase complex formation immunosorbent assay uses plate-bound elastase that is still proteolytically active. This elastase attacks functionally active AAT and forms a complex, which is then detected using an anti-AAT peroxidase conjugate. 

“Using three different approaches for the preparation of functionally inactive AAT – heating, oxidation, and complex formation with elastase – we confirmed beyond doubt that the [elastase complex formation immunosorbent assay] exclusively measures functionally active AAT and that these measurements are unimpaired by the presence of high concentrations of functionally inactive AAT,” the researchers wrote.

They then validated the functional activity of AAT that they determined using the elastase complex formation immunosorbent assay with a chromogenic elastase inhibition assay. The results matched well and the bioanalytical assay validation corresponded with the acceptance criteria for ligand-binding assays that current guidelines dictate.


Engelmaier A, Weber A. Sensitive and specific measurement of alpha1-antitrypsin activity with an elastase complex formation immunosorbent assay (ECFISA). J Pharm Biomed Anal. 2021;23:114476. doi:10.1016/j.jpba.2021.114476