Post-infectious glomerulonephritis (PIGN) is an immune-mediated kidney disease that develops following a systemic infection, most classically post-streptococcal glomerulonephritis (PSGN).
It is characterised by inflammation of the glomeruli due to immune complex deposition. Presentation is variable but it can lead to acute kidney injury (AKI), haematuria, proteinuria, and fluid retention. This used to be called nephritic syndrome.
Whilst historically most common in children after streptococcal infections, PIGN is increasingly seen in adults and older patients, often with more severe disease and less favorable outcomes.
Causes
Post-infectious glomerulonephritis occurs when an immune response to an infection leads to glomerular injury rather than direct infection of the kidney.
Infectious Triggers
Common causative organisms include:
- Group A beta-haemolytic Streptococcus
- Following pharyngitis or skin infections (impetigo)
- Staphylococcus aureus, especially in adults and patients with diabetes
- Other bacteria, viruses, and parasites:
- Pneumococcal species
- Gram-negative bacteria
- Hepatitis viruses
- HIV (less commonly)
Pathophysiology
- Circulating immune complexes form in response to infection
- Deposition occurs in the glomeruli
- Activation of the complement system, particularly the alternative pathway
- Resulting inflammation leads to reduced filtration and renal dysfunction
In adults, PIGN is often associated with ongoing or occult infection, rather than a fully resolved illness.
Symptoms
Symptoms of post-infectious glomerulonephritis typically develop 1–6 weeks after infection and vary significantly in severity.
Common Symptoms
- Haematuria, often gross (cola- or tea-colored urine)
- Oedema, particularly periorbital and peripheral
- Hypertension
- Decreased urine output
- Fatigue and malaise
Severe Presentations
- Acute kidney injury (AKI)
- Shortness of breath due to fluid overload
- Symptoms of hypertensive emergency
- Systemic signs of ongoing infection (more common in adults)
Children often have milder symptoms and a more benign course compared to adults.
Diagnosis
Diagnosis of post-infectious glomerulonephritis relies on clinical context, laboratory findings, and occasionally kidney biopsy.
Laboratory Tests
- Urinalysis: haematuria with red blood cell casts, mild to moderate proteinuria
- Serum creatinine: elevated in acute kidney injury
- Low complement levels, especially C3, with typically normal C4
- Elevated inflammatory markers in active infection
Evidence of Recent Infection
- Elevated antistreptolysin O (ASO) or anti-DNase B titres (streptococcal disease)
- Positive blood or tissue cultures in ongoing infections
Kidney Biopsy
- Usually reserved for atypical cases
- Shows diffuse endocapillary proliferation
- ‘Subepithelial humps’ on electron microscopy
- Granular immune complex deposition on immunofluorescence
Complement levels usually normalise within 6–8 weeks.
Treatment
Treatment of post-infectious glomerulonephritis is primarily supportive, with a focus on managing complications and treating any active infection.
Infection Management
- Appropriate antibiotic therapy for ongoing infection
- Eradication of infectious source to prevent continued immune activation
Supportive Renal Care
- Blood pressure control, often with diuretics or calcium channel blockers
- Fluid and sodium restriction
- Diuretics for oedema
- Temporary dialysis in severe cases (AKI)
Immunosuppression
- Generally not indicated
- May be considered in rare cases with rapidly progressive glomerulonephritis and biopsy-proven crescentic disease
Complications
Potential complications of post-infectious glomerulonephritis include:
- Acute kidney injury (AKI)
- Persistent hypertension (high blood pressure, BP)
- Chronic kidney disease, especially in adults
- Nephrotic-range proteinuria (uncommon but possible)
- Fluid overload and heart failure
Adults and older patients are at higher risk for incomplete recovery.
Outlook (Prognosis)
The prognosis of post-infectious glomerulonephritis depends on age, severity, and underlying health.
- Children: Excellent prognosis, with over 90% achieving full recovery
- Adults: Higher risk of persistent kidney dysfunction
- Poor prognostic indicators:
- Older age
- Severe acute kidney injury
- Persistent low complement levels
- Ongoing infection or comorbid conditions
Most patients experience gradual improvement in kidney function over weeks to months, although microscopic hematuria may persist longer.
