Alpha-1 antitrypsin (AAT) is an enzyme inhibitor made in the liver. Its primary function is to protect lung tissue from breakdown. Alpha-1 antitrypsin deficiency (AATD) is a genetic condition in which variant alleles lead to decreased serum levels of AAT. This causes decreased enzyme inhibition, which leads to lung tissue destruction and emphysema. Recognition of AATD is imperative, as it is treatable for some patients who can receive augmentation therapy to increase serum AAT levels. Serum AAT levels quantify the amount of AAT protein present in blood serum and can be assessed using nephelometry or latex-enhanced immunoturbidimetric assay. Different genetic variants of AATD produce a unique range of serum levels of AAT proteins. Quantification of AAT serum level alone is insufficient to assess AATD. Studies have shown that AAT levels have higher sensitivity for people with homozygous ZZ genotype, while sensitivity is lower for those with heterozygous genotypes.