CRP (C-Reactive Protein) is run on all patients concurrently with A1AT at no additional charge. CRP is an indicator of infection, inflammation or necrosis, all of which may cause a spurious A1AT elevation. If CRP positive, it is recommended that A1AT be retested in 10-14 days. Alpha-1 antitrypsin (A1AT) is a glycoprotein synthesized in the liver and is the main component of the alpha-1 globulins. A1AT deficiency may be associated with a characteristic lung disease which occurs early in life (i.e., juvenile emphysema). A1AT deficiency is one of the most frequent inborn metabolic errors. A1AT should be considered a positive "acute phase protein" because it rises whenever there is tissue injury, necrosis, inflammation, or infection. In acute phase reactions, A1AT increases within 12-24 hours, reaching maximum levels in 72-96 hours. Therefore, patients with A1AT deficiency who suffer from bronchitis, pneumonia, or similar respiratory inflammation are likely to have falsely normal levels during acute illness. A-1 antitrypsin quantitation should be run when alpha-1 globulin in serum protein electrophoresis is low. Heterozygous recessive A1AT patients exhibit A1AT levels which are commonly about 60% of normal. Homozygous recessive A1AT patients exhibit levels at about 10% of normal. Phenotyping is desirable on patients with low values, with abnormal alpha-1 globulin migration on serum protein electrophoresis, and on all patients being worked up for A1AT deficient liver disease. The most pathologic A1AT variant is homozygous ZZ.