Diagnostic and prognostic significance of proteinuria selectivity index in glomerular diseases

The proteinuria selectivity index (SI) describes changes of the glomerular permeability for macromolecules. In the present study, we examine the implications of SI as a diagnostic (199 patients) and a prognostic (49 patients) marker in glomerular diseases. Using SI based on α₂-macroglobulin (α₂-M-SI) or on IgM (IgM-SI) we found that minimal change nephropathy could be discriminated by low SI values and crescentic necrotizing glomerulonephritis by high SI values compared to other diseases. SI based on IgG (IgG-SI) was less useful in determining specific diagnoses. During a follow-up of 46 months creatinine clearance (Cr cl) decreased 36% in a group of patients with high IgG-SI (>0.2) and 38% in a group of patients with high IgM-SI (>1.5^-3) compared to only 8% in patients with low IgG-SI (≤0.2) or low IgM-SI (≤1.5^-3). Furthermore, Cr cl decreased more than 30% in 12 (92%) out of thirteen patients with high baseline levels of both IgG-SI and IgM-SI compared to three out of thirteen patients with low baseline values of both the indexes. The decline rate of Cr cl correlated significantly to the SI levels but not to the degree of albuminuria. The findings of the study indicate that urinary excretion of high-molecular-weight proteins, and not of albumin, is a potential prognostic marker in proteinuric glomerulopathies and it may also serve as valuable diagnostic aid in these disorders. (C) 2000 Elsevier Science B.V.