As a type of enzyme inhibitor, it protects tissues from enzymes of inflammatory cells, especially neutrophil elastase, and has a reference range in blood of 0.9–2.3 g/L (in the US the reference range is expressed as mg/dL or micromoles), but the concentration can rise manyfold upon acute inflammation.
The level of A1AT in serum is most often determined by adding an antibody that binds to A1AT, then using turbidimetry to measure how much A1AT is present.
Other detection methods include the use of enzyme-linked-immuno-sorbent-assays and radial immunodiffusion.
A low level of AAT in blood indicates that the person tested may have alpha-1 antitrypsin deficiency. The lower the level of AAT, the greater the risk of developing emphysema and other disorders related to AAT deficiency.
In people with an abnormal form of AAT, the risk of developing disease depends on how much is produced and which variant is present. A variant with very low activity may lead to both emphysema (because it does not protect the lungs) and liver disease (because of the buildup of abnormal AAT inside liver cells).