Clinicopathological Spectrum of Adult Glomerulonephritis With Predominant C3 Deposition: A Four-Case Series Favoring Infection-Related Glomerulonephritis

Infection-related glomerulonephritis (IRGN) in adults is a heterogeneous clinicopathological entity with generally less favorable renal outcomes than classic post-streptococcal glomerulonephritis in children.Predominant C3 deposition on kidney biopsy can pose a diagnostic challenge because it may closely mimic C3 glomerulopathy (C3G), particularly when the infectious trigger is remote, partially treated, or not well documented.We report a series of four adults with biopsy-proven glomerulonephritis showing predominant C3 deposition and clinicopathological features favoring an infection-related process.Clinical presentations were heterogeneous, ranging from acute kidney injury with nephrotic syndrome and crescentic glomerulonephritis to persistent microscopic hematuria and subnephrotic proteinuria with preserved kidney function.Kidney biopsy demonstrated diverse histopathological patterns, while immunofluorescence consistently showed predominant C3 deposition with absent or trace immunoglobulin staining.Renal function improved substantially in two patients and remained preserved in two patients, although longterm follow-up was incomplete in one patient.Cases 2 and 4 represented the main diagnostic challenge because of persistent urinary abnormalities in the absence of a documented active infection and incomplete complementary investigations, and C3G could not be definitively excluded.This case series highlights the heterogeneous clinicopathological spectrum of adult glomerulonephritis with predominant C3 deposition and emphasizes the importance of integrating clinical history, microbiological investigations, complement evaluation, kidney biopsy findings, and clinical evolution to distinguish IRGN from C3G. Accurate clinicopathological correlation is essential because this distinction has important therapeutic and prognostic implications.