Interestingly, this threshold level was first described by radial immunodiffusion, which suggests that that AAT levels ≤50 mg/dL are associated with a high risk for the development of emphysema, levels between 50 and 80 mg/dL confer an uncertain risk, and levels >80 mg/dL confer no increase in risk above the background risk [8]. Here, SERPINA1 is linked to pulmonary emphysema.