⚠️ High-Yield Board Point: PSGN: Acute nephritic syndrome 1–3 weeks post-strep; child/young adult; low C3 (classic), normal C4; most recover completely. IRGN (IgA-dominant): Elderly, diabetic, immunocompromised; staphylococcal infection more common; IgA-dominant on biopsy; poor prognosis (30–50% progress to ESRD). Both: hematuria + proteinuria + AKI; supportive care.
Epidemiology and Epidemiologic Shift
Classic PSGN (Historical)
- Predominantly children (age 3–12)
- Post-streptococcal pharyngitis (Group A Strep)
- Endemic in developing regions
Modern Epidemiology
- Shift to adults, particularly elderly
- S. aureus most common (30–80% of adult cases)
- IgA-dominant IRGN now recognized (17% of IRGN)
- Associated with: diabetes, CKD, IV drug use, healthcare-associated infections
Pathophysiology and Pathology
Kidney Biopsy Findings
| Modality | Finding |
|---|
| Light Microscopy | Endocapillary proliferation (most characteristic); neutrophil-rich exudative lesions |
| Immunofluorescence | C3-dominant staining (hallmark); IgA-dominant pattern in IRGN subset |
| Electron Microscopy | Subepithelial "humps" (classic PSGN finding) |
Clinical Presentation
Classic PSGN (Children)
- Recent streptococcal infection 1–3 weeks prior
- Hematuria: Gross ("cola-colored") in ~50%; microscopic in remainder
- Proteinuria: Usually <3.5 g/day (non-nephrotic)
- Hypertension: ~50% of children; reflects volume expansion
- Edema: Periorbital most common
Adult-Onset IRGN (Often Indolent)
- Preceding infection often non-apparent or chronic staphylococcal
- Diabetes, CKD, or immunocompromised often present
- Nephrotic-range proteinuria in 30–50% (more common than PSGN)
- AKI present in ~98%
📚 Key Point: Adult-onset IRGN often presents with nephrotic syndrome (heavy proteinuria) in contrast to pediatric PSGN (typically nephritic, non-nephrotic proteinuria). This difference reflects IgA-dominant IRGN pathology vs. classic PSGN.
Diagnosis
Serologic Markers
- ASO titer: Elevated in ~80% of PSGN; peaks 3–5 weeks post-infection
- Anti-DNase B: More sensitive for streptococcal skin infection (pyoderma)
- Serial titers (2-week interval) more diagnostic than single elevated titer
Complement Levels
- Classic: low C3, normal C4 (alternative pathway activation)
- C3 normalizes over 6–8 weeks in ~90% of cases
- Persistent low C3 (>12 weeks): Suggests alternative diagnosis (lupus, MPGN, C3 glomerulopathy)
📚 Clinical Pearl: Low C3 that normalizes is reassuring for PSGN prognosis; persistent low C3 warrants additional evaluation for alternative diagnoses.
PSGN vs. IRGN: Key Differences
| Feature | PSGN (Child) | IRGN (Adult, esp. IgA-dominant) |
|---|
| Age | 3–12 years | >50 years |
| Infection type | Streptococcal | Staphylococcal (chronic) |
| Presentation | Acute nephritic | Nephritic or nephrotic |
| C3 level | Low, normalizes <12 weeks | Normal or persistent low |
| IF pattern | C3-dominant | IgA-dominant |
| Recovery rate | >95% complete | 40–50% complete |
| CKD progression | <1% | 20–30% |
Management
1. Treat Underlying Infection (Critical First Step)
- Streptococcal: Penicillin G or amoxicillin x 10 days
- Staphylococcal: Nafcillin/oxacillin (or vancomycin if MRSA); 4–6 weeks if endocarditis
2. Supportive Care (Mainstay)
- Sodium restriction (<2 g/day)
- Diuretics for edema/hypertension
- ACE-I/ARB for proteinuria reduction (target BP <130/80)
- Avoid nephrotoxins (NSAIDs, aminoglycosides, contrast)
3. Immunosuppression (NOT Routine)
- Pediatric PSGN: NOT recommended (excellent prognosis)
- Adult IRGN: Individualized; not established standard
- RPGN with crescents: Some experts treat with steroids +/- cyclophosphamide
📚 Clinical Pearl: Do not assume adult-onset IRGN will recover completely like childhood PSGN. Adult patients, especially if elderly/diabetic/with baseline CKD, require close long-term follow-up (6–12 months minimum) with serial Cr, urinalysis, and proteinuria measurement.
Monitoring and Follow-Up
| Population | Schedule | Tests |
|---|
| Pediatric PSGN | Monthly x 3, then q3 months x 1 year | UA, Cr/eGFR, BP. Full resolution expected by 12 months. |
| Adult IRGN | Baseline, 2 weeks, 1 month, then q3 months x 1 year | UA, UACR, Cr/eGFR, BP, complement at 6 & 12 weeks. Consider 2–5 year follow-up. |
References
- KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases. Kidney Int. 2021;100(4S):S1-S276. DOI
- Nasr SH, et al. IgA-dominant acute poststaphylococcal glomerulonephritis complicating diabetic nephropathy. Hum Pathol. 2003;34(12):1235-1241. PubMed
- Nasr SH, et al. Postinfectious glomerulonephritis in the elderly. JASN. 2011;22(1):187-195. PubMed
- Rodriguez-Iturbe B, Musser JM. The current state of poststreptococcal glomerulonephritis. JASN. 2008;19(10):1855-1864. PubMed
- Sethi S, et al. Infection-related glomerulonephritis: changing demographics and outcomes. Adv Chronic Kidney Dis. 2012;19(2):68-75. PubMed Search
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