SERPINA1 and alpha 1-antitrypsin deficiency: In addition, as AAT deficiency only has 1 International Classification of Diseases code (E88.01), it may potentially include carriers of the Z allele (allele associated with very low AAT levels in the blood; homozygous ZZ patients are at high risk of developing emphysema and liver disease) who are then documented as receiving a transplant due to a diagnosis of AAT deficiency.