What are the diagnostic criteria for post-streptococcal glomerulonephritis (PSGN)?

Diagnostic Criteria for Post-Streptococcal Glomerulonephritis (PSGN)

The diagnosis of post-streptococcal glomerulonephritis requires evidence of recent streptococcal infection (pharyngitis 1-2 weeks prior or impetigo 4-6 weeks prior), clinical features of glomerulonephritis, and laboratory findings showing low complement levels and elevated streptococcal antibodies. 1

Clinical Presentation

• Evidence of recent streptococcal infection: pharyngitis (1-2 weeks prior) or impetigo (4-6 weeks prior) 2, 1
• Acute onset of nephritic syndrome characterized by:
  • Hematuria (microscopic or macroscopic) with red blood cell casts 2, 3
  • Proteinuria (variable severity, can range from mild to nephrotic range) 3, 4
  • Hypertension (present in up to 95% of cases in acute phase) 5
  • Edema (due to fluid retention) 3
  • Decreased urine output 3
• Note: Some cases may present with minimal urinary abnormalities, so normal urinalysis does not rule out PSGN 6

Laboratory Criteria

• Urinalysis:
  • Glomerular hematuria with red blood cell casts 2
  • Proteinuria (measure albumin-creatinine ratio or protein-creatinine ratio) 2
• Serological evidence of streptococcal infection:
  • Elevated anti-streptolysin O (ASO) titers 2, 7
  • Elevated anti-DNAse B antibodies 2
  • Elevated anti-hyaluronidase antibodies 2
• Complement studies:
  • Low C3 complement levels (hallmark finding) 2, 1, 7
  • C4 typically normal (helps differentiate from other forms of glomerulonephritis) 2
  • Persistently low C3 beyond 12 weeks warrants kidney biopsy to exclude C3 glomerulonephritis 2
• Kidney function tests:
  • Elevated serum creatinine and decreased eGFR (in severe cases) 2, 3

Microbiological Criteria

• Culture of throat or skin lesions if active infection is present 2
• Positive cultures may not be obtained if presentation occurs weeks after the initial infection 2, 1

Histopathological Criteria (if biopsy performed)

• Diffuse proliferative glomerulonephritis 3
• Neutrophil infiltration 7
• Subepithelial "humps" on electron microscopy (pathognomonic) 7
• Positive immunofluorescence for C3 and IgG 7
• Presence of nephritis-associated plasmin receptor (NAPlr) in some cases 7
• Crescents may be present in severe cases (poor prognostic sign) 3, 4

Differential Diagnosis Exclusion

• Rule out other causes of nephritis:
  • Antinuclear antibody (ANA) negative 2
  • Anti-neutrophil cytoplasmic antibody (ANCA) negative 2
  • Anti-glomerular basement membrane (GBM) antibody negative 2
  • Normal rheumatoid factor and cryoglobulins 2

Special Considerations

• Kidney biopsy is indicated when:
  • Diagnosis is uncertain 2
  • Atypical presentation 2
  • Persistently low C3 beyond 12 weeks 2
  • Rapidly progressive course 4
  • Nephrotic-range proteinuria 4
• Histological diversity exists - some cases may present as membranoproliferative glomerulonephritis (MPGN) 7

Prognostic Indicators

• Poor prognostic factors include:
  • Crescent formation on biopsy 3
  • Renal insufficiency at presentation 3
  • Hypoalbuminemia 3
  • Elevated C-reactive protein 3
  • Persistent hypertension during disease evolution 5

Remember that while PSGN is typically self-limiting with supportive care, patients with severe presentations (crescentic glomerulonephritis, nephrotic syndrome) may require more aggressive management and closer monitoring 4.