PROTEINURIA SELECTIVITY INDEX BASED UPON ALPHA(2)-MACROGLOBULIN OR IGM IS SUPERIOR TO THE IGG BASED INDEX IN DIFFERENTIATING GLOMERULAR-DISEASES - TECHNICAL NOTE

Background. The proteinuria selectivity index (SI) may be used to desc ribe changes of the glomerular permeability for macromolecules in glom erular diseases. Proteins the size of alpha(2)-macroglobulin (alpha(2) M) or IgM cannot normally pass the glomerular barrier, whereas IgG can pass through the large pores of glomerular basement membrane. Compari son of the clearance of the three high-molecular-weight proteins to th at of albumin may be useful in characterization and diagnosis of diffe rent glomerular diseases as well as in understanding of the permeabili ty characteristics of the glomerular filter. Methods. Three types of S I, each calculated as a ratio of clearance of either IgG, alpha(2)M or IgM to that of albumin, were measured in 199 proteinuric patients. Th e patients were subdivided into eight different biopsy-verified glomer ular diseases. Results. Two diagnoses could be clearly distinguished u sing SI based on alpha(2)M (alpha(2)M SI) or IBM (IgM SI). Both alpha( 2)M SI and IgM SI were significantly lower in minimal change nephropat hy and higher in crescentic necrotizing glomerulonephritis than in all the other diagnoses. The SI based on IgG (IgG SI) was less useful in determining specific diagnoses, since patients with minimal change nep hropathy could not be distinguished from those with other types of pri mary glomerulonephritis and patients with crescentic necrotizing glome rulonephritis did not differ from those with diabetic nephropathy. Con clusions. The findings of this study indicate that alpha(2)M SI and Ig M SI are superior to IgG SI in characterization of glomerular disorder s and might replace the Ige SI for this purpose.