Post-streptococcal Acute Glomerulonephritis

An immune-mediated glomerular disease that occurs 1–3 weeks after infection with nephritogenic strains of group A β-hemolytic Streptococcus

Aetiology

  • Causative Organism
    • Group A β-hemolytic Streptococcus (Streptococcus pyogenes)
  • Nephritogenic Strains
    • M protein types:
      • Pharyngitis: M types 12, 4, 1
      • Impetigo: M types 49, 55, 57

Pathophysiology

  1. Streptococcal infection triggers immune response
  1. Formation of circulating immune complexes containing streptococcal antigens (e.g., nephritis-associated plasmin receptor, streptococcal pyrogenic exotoxin B)
  1. Deposition of immune complexes in the glomeruli
  1. Activation of complement (mainly alternative pathway)
  1. Glomerular inflammation → ↓ GFR → hematuria, hypertension, edema
Key feature: Low serum C3 levels, which typically normalize within 6–8 weeks

Clinical presentation

Latent Period

  • 1–2 weeks after streptococcal pharyngitis
  • 3–6 weeks after streptococcal skin infection

Renal Manifestations (Nephritic Syndrome)

  • Cola-colored or smoky urine
  • Oliguria
  • Mild to moderate proteinuria
  • Periorbital and dependent edema
  • Hypertension

Systemic Features

  • Malaise
  • Headache
  • Nausea and vomiting
  • Features of fluid overload (pulmonary edema in severe cases)

Investigations

A. Urinalysis

  • Hematuria with dysmorphic RBCs
  • Red blood cell casts
  • Mild to moderate proteinuria

Blood Tests

  • Elevated serum creatinine and urea
  • Low C3 complement levels (hallmark)
  • Elevated antistreptococcal antibodies:
    • ASO titer (post-pharyngitis)
    • Anti-DNase B (post-impetigo)
  • Mild normocytic normochromic anemia

Imaging

  • Renal ultrasound: normal or mildly enlarged kidneys

Renal Biopsy (Rarely Required)

Indicated if:
  • Atypical presentation
  • Persistent hypocomplementemia (>8 weeks)
  • Rapidly progressive renal failure
Histology:
  • Light microscopy: diffuse endocapillary proliferative GN
  • Immunofluorescence: granular (“starry sky”) IgG and C3 deposits
  • Electron microscopy: subepithelial humps (pathognomonic)

Management

Supportive Treatment (Mainstay)

  • Salt and fluid restriction
  • Loop diuretics for edema
  • Antihypertensive therapy (e.g., calcium channel blockers)
  • Careful monitoring of renal function and urine output

Antibiotic Therapy

  • Amoxicillin 50mg/kg/day divided in 3 doses for 7-10 days
  • Erythromycin 30mg/kg/day divided in 3 doses for 7-10 days
  • Does not alter renal course, but prevents transmission and rheumatic fever

Renal Replacement Therapy

  • Indicated in severe cases with:
    • Refractory hyperkalemia
    • Severe acidosis
    • Fluid overload
    • Uremic complications