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 alpha(2)-macroglobulin (alpha(2)-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.