AAT Phenotype Identification by Isoelectric Focusing.

Isoelectric focusing (IEF) electrophoresis is considered to be the gold standard test for determining an individual's AAT phenotype. IEF electrophoresis is a technique used to separate proteins by differences in their isoelectric point (pI). Testing is performed on serum that is applied to an agarose gel containing ampholytes which create a pH gradient ranging from 4.2 to 4.9. Variants of AAT are therefore separated from each other and, after visualization of the focused protein bands using immunochemical techniques, can be identified and an AAT phenotype determined.In this chapter we elaborate on IEF electrophoresis as it relates to AAT phenotyping, describe practical approaches to AAT variant identification, and discuss circumstances in which phenotype testing may be inaccurate.