Serum levels of alpha1-antitrypsin predict phenotypic expression of the alpha1-antitrypsin gene.

We conducted a retrospective analysis to determine if both alpha1-antitrypsin serum level and phenotype need be studied when evaluating children for alpha1-AT deficiency. We collected data from patients less than 19 years old who had both serum alpha1-AT level and phenotype determined over a 9-year period (January 1992-December 2000). Eighty-eight patients were identified and 15 had the PiZZ phenotype. The serum alpha1-AT level was below normal (normal 85-215 mg/dl) in all 15 PiZZ patients. Seventy-two of 73 non-PiZZ patients had normal or above normal serum levels. The sensitivity of the serum alpha1-AT level was 100%, and the specificity was 99%. The serum alpha1-AT level had a positive predictive value of 94% and a negative predictive value of 100%. We conclude that serum alpha1-AT levels are highly predictive of the PiZZ phenotype. Determination of the serum alpha1-AT level alone should be the initial test when evaluating for alpha1-AT deficiency.