Alpha-1-Antitrypsin (AAT) blood test is used to diagnose Alpha-1-Antitrypsin Deficiency (AATD). Alpha-1-Antitrypsin protein is produced in the liver, and protects the lungs against certain infections. The symptoms of AATD are associated with lung and liver diseases, with signs like breathing difficulty, sudden weight loss, fatigue, recurrent respiratory infections, pale skin, elevated liver enzymes, abdominal swelling, and jaundice.