Post-Streptococcal Glomerulonephritis (PSGN)
Immune complex GN 1-3 weeks after group A strep pharyngitis or impetigo.
Also known as: PSGN, post-streptococcal GN, acute post-infectious GN
Overview
An immune complex-mediated glomerulonephritis occurring 1-3 weeks after infection with nephritogenic strains of group A beta-hemolytic streptococcus (GAS), typically pharyngitis or skin infection (impetigo). Presents with classic nephritic syndrome.
Epidemiology
Most common cause of acute glomerulonephritis in children worldwide. Peak age 4-12 years. Incidence has declined in developed countries with early antibiotic treatment of strep infections. Adults can be affected, with worse prognosis. Outbreaks may follow skin infection epidemics.
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Risk factors
- Recent group A streptococcal pharyngitis (latency 1-2 weeks)
- Recent streptococcal skin infection — impetigo, pyoderma (latency 3-6 weeks)
- Crowded living conditions
- Pediatric age (school-aged children)
- Tropical/subtropical climates (impetigo predominant)
Pathophysiology
Nephritogenic strains of GAS (M types 1, 4, 12 in pharyngitis; M types 47, 49, 55 in impetigo) produce antigens (notably streptococcal pyrogenic exotoxin B and nephritis-associated plasmin receptor) that form circulating immune complexes or deposit in situ in subepithelial glomerular sites. Complement activation (alternative pathway predominantly) drives inflammation, mesangial and endothelial proliferation.
Clinical presentation
Symptoms
- Abrupt onset of tea-colored or cola-colored urine (gross hematuria) 1-3 weeks after pharyngitis or 3-6 weeks after impetigo
- Periorbital edema, especially in the morning
- Decreased urine output
- Headache and malaise from hypertension
- Children may have nonspecific symptoms initially
Signs / physical exam
- Hypertension (50-90% of children)
- Periorbital and dependent edema
- Tea-colored or smoky urine
- Mild tenderness over flanks (uncommon)
- Healed strep infection — pharyngeal exam often normal at presentation
Classic findings
Cola-colored urine + periorbital edema + hypertension in a child 1-3 weeks after sore throat or impetigo = classic PSGN.
Differential diagnosis
- IgA nephropathy — Synpharyngitic hematuria (within 1-3 days, not 1-3 weeks); normal complement; recurrent episodes
- Lupus nephritis — Systemic SLE features; ANA, anti-dsDNA; low C3 AND C4
- Membranoproliferative GN — Persistent low complement; hepatitis C, cryoglobulinemia
- ANCA vasculitis — Constitutional symptoms, sinopulmonary involvement; positive ANCA; normal complement
- Henoch-Schönlein purpura (IgA vasculitis) — Palpable purpura, arthralgia, abdominal pain; normal complement
- Other post-infectious GN — After staph, gram-negative, or viral infections; similar pathology
Diagnostic workup
Diagnostic criteria
Clinical diagnosis: nephritic syndrome + recent strep infection + low C3 + positive streptococcal serology. Biopsy reserved for atypical presentations (persistent low C3 >8 weeks, severe AKI, RPGN features) and shows endocapillary proliferative GN with subepithelial 'humps' on EM and granular IgG/C3 on IF.
Labs
- Urinalysis: hematuria with dysmorphic RBCs and RBC casts, mild-moderate proteinuria (typically subnephrotic), pyuria
- BMP: elevated creatinine, sometimes hyperkalemia
- Low C3 (90%), normal C4 — pathognomonic complement pattern
- Streptococcal serologies: ASO (positive in 60-80% after pharyngitis but less so after skin infection), anti-DNase B (more sensitive after impetigo), anti-hyaluronidase, anti-streptokinase
- Throat culture or skin culture (often negative by time of GN presentation)
- Streptozyme test combines multiple antibodies
Imaging
- Renal ultrasound usually unnecessary; normal or mildly enlarged kidneys
Diagnostic algorithm
| Feature | PSGN | IgA Nephropathy |
|---|---|---|
| Latency after infection | 1-3 wk (pharyngitis); 3-6 wk (skin) | 1-3 days (synpharyngitic) |
| Age | Children 4-12 yr (mainly) | Young adults |
| Complement C3 | Low (resolves in 6-8 wk) | Normal |
| Serology | ASO, anti-DNase B positive | Elevated IgA (~50%) |
| Course | Self-limited (children); residual in adults | Chronic, relapsing |
| Biopsy IF | Granular IgG/C3, 'humps' on EM | Mesangial IgA deposits |
| Prognosis | >95% recovery in children | 20-40% ESRD over 20 yr |
Treatment
First-line
- Supportive care — most cases resolve spontaneously
- Sodium and fluid restriction for volume overload
- Loop diuretic — furosemide — for edema and hypertension
- Antihypertensives: CCB (amlodipine) or ACEi (if renal function stable); hydralazine or nicardipine for hypertensive emergency
- Antibiotics (penicillin V, amoxicillin, or erythromycin if allergic) if active strep infection still present — does NOT alter renal course but limits transmission
Second-line / adjunct
- Dialysis temporarily if severe AKI with hyperkalemia, uremia, or refractory volume overload (rare)
- Glucocorticoids only if biopsy shows crescents (atypical RPGN course)
- Monitor C3 — should normalize within 6-8 weeks; persistent low C3 should prompt alternative diagnosis (MPGN, lupus)
- Family screening of household contacts for active strep infection
- Long-term BP and proteinuria monitoring
Complications
- Hypertensive emergency, posterior reversible encephalopathy syndrome (PRES)
- Volume overload, pulmonary edema, congestive heart failure
- Acute kidney injury requiring temporary dialysis (rare)
- Rapidly progressive crescentic GN (atypical)
- Adults: 25-50% may have persistent abnormalities (proteinuria, hypertension, CKD)
- Children: excellent prognosis with >95% complete recovery
PANCE pearls
- Low C3 + normal C4 is the classic complement signature; should normalize within 6-8 weeks. Persistent low C3 → consider MPGN or lupus.
- ASO titer rises after pharyngitis but not reliably after skin infection — order anti-DNase B for impetigo-associated cases.
- Antibiotics for the strep infection do NOT prevent or alter PSGN (unlike rheumatic fever, which IS prevented by antibiotics).
- Children have excellent prognosis; adults have worse outcomes with 25-50% having residual abnormalities.
- Hematuria can persist for months; proteinuria may persist longer. Hypertension and edema typically resolve within 1-2 weeks.
References
- KDIGO 2021 — KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases
- Eison 2011 — Post-streptococcal acute glomerulonephritis in children (Eison et al., Pediatr Nephrol 2011)
- Rodríguez-Iturbe — Pathogenesis of poststreptococcal glomerulonephritis (Rodríguez-Iturbe and Musser, JASN 2008)
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