Improved classification of proteinuria by semiautomated ultrathin SDS polyacrylamide gel electrophoresis

The quantitative and qualitative analysis of proteinuria by electrophoretic means proved to be a potent diagnostic tool for differentiation of functional renal impairment. The purpose of this study was to compare the macro scale SDS-PAGE technique, which has been used for the last two decades, with semiautomated electrophoresis using an ultrathin SDS-PAA gel with silver staining (Phast system). The new system proved to be quick and easy to handle. Separation of proteins in the range of 70-320 kD were of comparable quality to the macro scale system (unselective and selective glomerular proteinurias with 68 to 150 and 68 to 350 kD components, respectively, as well as total serum proteins), but there was considerable improvement regarding the quality and visibility of protein bands in the range of 11-70 kD. This improvement led to a new classification of micromolecular protein bands into three groups: the smallest microproteins (11-22 kD), the larger microproteins (23-40 kD) and the largest microproteins (41-68 kD). Thereby it was possible to obtain an improved definition of electrophoretic patterns of urinary proteins, which is described in detail.