Post-streptococcal glomerulonephritis (PSGN)
Also known as: PSGN, acute poststreptococcal glomerulonephritis
Post-streptococcal glomerulonephritis (PSGN) is an immune complex-mediated kidney disease that follows infection with group A Streptococcus, classically presenting with dark urine, edema, and hypertension. It most often affects children weeks after strep throat or a skin infection.
Post-streptococcal glomerulonephritis is a type III hypersensitivity reaction in which immune complexes formed after infection with nephritogenic strains of group A Streptococcus (Streptococcus pyogenes) deposit in the glomeruli, triggering complement activation and inflammation. It classically appears about 1–3 weeks after streptococcal pharyngitis or 3–6 weeks after a streptococcal skin infection such as impetigo, most commonly in children.
The presentation is a nephritic syndrome: cola- or tea-colored urine from hematuria, periorbital and peripheral edema, hypertension, oliguria, and mild proteinuria. Laboratory findings include depressed serum C3 complement with normal C4, elevated anti-streptolysin O (ASO) and anti-DNase B titers confirming recent strep infection, and red blood cell casts on urinalysis. On biopsy, immunofluorescence shows a granular "starry sky" pattern of IgG and C3, and electron microscopy shows the characteristic subepithelial electron-dense humps.
Prognosis differs sharply by age: children usually recover completely with supportive management of blood pressure and fluid status, while adults face a higher risk of persistent renal impairment. PSGN sits alongside acute rheumatic fever as one of the two major post-streptococcal sequelae — and unlike rheumatic fever, prior antibiotic treatment of the strep infection does not reliably prevent it.
The USMLE Step 1 tests PSGN in both the renal pathology and microbiology contexts — know the timeline after pharyngitis versus impetigo, the low C3, the subepithelial humps, and how PSGN is distinguished from other nephritic syndromes such as IgA nephropathy, which recurs within days of infection rather than weeks.
Key takeaways
- PSGN is an immune complex (type III hypersensitivity) glomerulonephritis following group A strep infection.
- It appears about 1–3 weeks after strep pharyngitis or 3–6 weeks after strep skin infection, most often in children.
- Classic findings: cola-colored urine, periorbital edema, hypertension, low serum C3, and elevated ASO or anti-DNase B titers.
- Electron microscopy shows subepithelial humps; immunofluorescence shows a granular starry-sky pattern.
- Children usually recover fully, while adults have a higher risk of lasting renal impairment.