Diagnosis: Acute Postinfectious Glomerulonephritis
• The classic presentation of acute postinfectious glomerulonephritis (APIGN) includes acute nephritis (i.e., acute renal failure, hematuria, hypertension, fluid overload) and hypocomplementemia approximately 2 weeks after an upper respiratory tract infection.
• The most common etiology of APIGN in children is streptococcal pharyngitis resulting from group A β-hemolytic streptococcal infection. Most children have a complete recovery.
• On light microscopy, APIGN typically manifests a diffuse proliferative glomerulonephritis with numerous infiltrating neutrophils.
• The deposits of APIGN stain dominantly or codominantly for C3 on immunofluorescence, with weaker and more variable staining for IgG.
• The most characteristic finding in APIGN on ultrastructural evaluation is subepithelial “hump-shaped” electron-dense deposits. Compared with the subepithelial deposits seen in membranous nephropathy, the subepithelial deposits in APIGN are larger, are less numerous, have a “hump-shaped” appearance, and are not associated with intervening glomerular basement membrane (GBM) spikes.
