Post-Streptococcal Glomerulonephritis

Key points

• Post-streptococcal GN classically occurs after a nephritogenic group A streptococcal infection; the typical latency is about 7–15 days after pharyngitis and about 4–6 weeks after impetigo .
• Evidence of recent streptococcal infection may include raised ASO and/or anti-DNase B titres; the appropriate antibody depends partly on the preceding site of infection. Low C3 is characteristic during the acute phase.
• Histology: acute endocapillary proliferative/exudative GN with inflammatory cells; the classic lesion is not simply 'endothelial proliferation'.
• Electron microscopy: subepithelial electron-dense 'humps' are a classic finding.
• Immunofluorescence: granular IgG/C3 deposition, classically described as a 'starry sky' or 'lumpy-bumpy' pattern.
• Prognosis: generally excellent in children, but adults—especially older or comorbid patients—can have a worse outcome.
• MRCP distinction from IgAN: post-streptococcal GN follows a latent interval and usually has low C3; IgAN is typically synpharyngitic with normal complement.
• MRCP discriminator: child with oedema + hypertension + cola urine 1–3 weeks after sore throat, low C3 and raised streptococcal antibodies → post-streptococcal GN.
• High-yield: persistent low C3 beyond the expected recovery period should prompt reconsideration of the diagnosis and possible further investigation.