What does the kidney biopsy show in SAAG?
By light microscopy it may be difficult to distinguish PSGN from SAAG, as both present with a diffuse exudative glomerulonephritis with extensive neutrophilic infiltrate.
The key histologic finding in SAAG is seen on immunofluorescence, which demonstrates predominant IgA staining at the site of the deposits.
IgG may also be present, but it is often overshadowed by the IgA staining. Other infections causing glomerulonephritis may be associated with a predominant IgA response, but S. aureus accounts for the vast majority of these cases.
In some instances, only C3 is present on immunofluorescence, which can confuse the differential diagnosis by adding C3 glomerulopathy.
Electron microscopy shows subepithelial deposits similar to PSGN as well as scattered sub-endothelial and mesangial deposits.
Both SAAG and PSGN share similar findings on electron microscopy.
