IgA Staining Patterns Differentiate Between IgA Nephropathy and IgA-Dominant Infection-Associated Glomerulonephritis

Background: Differential diagnosis of primary IgA nephropathy (IgAN) and IgAdominant infection-related glomerulonephritis, particularly Staphylococcus infectionassociated glomerulonephritis (SAGN), on a kidney biopsy can be challenging because of similar morphologic findings by light microscopy, immunofluorescence and electron microscopy. Clinical management approach however, is very different. Immunosuppressive therapy is contraindicated in SAGN because it can lead to sepsis and even death. Antibiotics constitute the first line of therapy. In contrast to that, primary IgAN is treated either with conservative management or with immunosuppression. There are no specific biomarkers to distinguish between these two diseases. Methods: Kidney biopsies from patients with IgAN or SAGN were analyzed. Immunofluorescence with an antibody to IgA was performed on sections of frozen and paraffin embeded tissue. Results: In total, 75 biopsies (45 with IgAN and 30 with SAGN) were evaluated. All 75 biopsies showed distinct granular staining for IgA in the non-sclerotic glomeruli (Figure 1). Globally sclerosed glomeruli were identified in 47 biopsies (29 with IgAN and 18 with SAGN). Among the 29 biopsies of IgAN, 20 (69%) had positive granular staining for IgA in the globally sclerosed glomeruli and 9 (31%) cases did not. Among the 18 kidney biopsies with SAGN, only one case (5.6%) showed positive staining for IgA in globally sclerosed glomeruli, whereas the remaining 17 (94.4%) did not (Table 1). The sensitivity of positive IgA staining in globally sclerosed glomeruli for kidney biopsies with IgAN was 68.97%, specificity was 94.44%.Table 1.: Distribution of staining for IgA in sclerotic glomeruli between cases with IgAN and SAGNConclusions: Evaluation of IgA staining in sclerosed glomeruli can help to differentiate between primary IgAN and SAGN in the right clinical context, and aid in patient management in most cases