Chapter 8 – Laboratory Diagnosis

Alpha1-antitrypsin (AAT) deficiency (AATD) should be suspected in any person who presents with early onset COPD (especially emphysema), regardless of her/his smoking history, in those individuals with unexplained liver disease at any age, including obstructive jaundice of infancy, and in patients with severe bronchial asthma, systemic vasculitis, or neutrophilic panniculitis. Definitive diagnosis involves a quantification of the serum AAT concentration. If serum AAT concentration is below the reference value, two strategies for laboratory testing can be used: (1) plasma AAT phenotyping by isoelectric focusing (IEF) which allows identification of the most common AAT variants, and (2) genotyping by allele-specific PCR method which allows identification of the most common AATD alleles: Pi*S and Pi*Z. Molecular analysis with direct sequencing of the whole SERPINA1 gene (genotyping) is the reference method for identifying rare and null deficiency allelic variants. The dried blood spot specimens are now being successfully used for large-scale AATD diagnostics, as an easy to collect and transport alternative to plasma/serum that provides enough sample to measure serum AAT and to perform IEF, as well as sufficient quantity and quality of DNA to detect Pi*S and Pi*Z alleles in a single real-time PCR and direct sequencing.