Diagnosis: Acute Post-Streptococcal Glomerulonephritis (APSGN)
This clinical presentation is classic for acute post-streptococcal glomerulonephritis (APSGN), also known as postinfectious glomerulonephritis following streptococcal pharyngitis. The constellation of recent strep pharyngitis, hematuria, elevated creatinine, and proteinuria with blood on urinalysis defines this diagnosis 1.
Diagnostic Criteria and Confirmation
The diagnosis of APSGN is established when a patient presents with:
- Acute glomerulonephritis (hematuria + proteinuria, as in this case)
- Recent streptococcal infection (pharyngitis, as documented here)
- Transient hypocomplementemia (low C3 levels) 1
Essential Laboratory Workup
To confirm APSGN and assess severity, obtain 2, 1:
- Complement C3 and C4 levels - C3 will be low; C4 typically normal
- Anti-streptolysin O (ASO) titers or anti-DNAse B antibodies - elevated in streptococcal infection 2, 3
- Complete urinalysis - assess for glomerular hematuria and red blood cell casts 2
- Serum creatinine and eGFR - quantify kidney injury
- Serum albumin - assess for nephrotic-range proteinuria 1
- Complete blood count - evaluate for anemia
- Blood pressure measurement - hypertension is common 1
Timing and Pathophysiology
APSGN typically presents 1-2 weeks after pharyngitis or 4-6 weeks after skin infection (impetigo) 2. This latent period reflects the immune-mediated nature of the disease, where immune complex deposition in glomeruli causes the kidney injury 4.
When Kidney Biopsy is Required
Kidney biopsy is NOT routinely needed for typical APSGN but is indicated for 2, 1:
- Persistently low C3 beyond 12 weeks (suggests alternative diagnosis like C3 glomerulonephritis)
- Nephrotic syndrome (massive proteinuria with hypoalbuminemia)
- Rapidly progressive glomerulonephritis (RPGN) with rapid creatinine rise
- Atypical features that raise diagnostic uncertainty
- Persistent proteinuria ≥2+ for more than 2 weeks with creatinine >100 μmol/L 5
Histological Findings When Biopsy is Performed
If biopsy is done, expect diffuse proliferative glomerulonephritis with immunofluorescence showing IgG and C3 deposition 5. Crescents may be present in severe cases (<50% in most, but >50% indicates crescentic GN requiring different management) 5.
Clinical Pitfalls and Red Flags
Critical caveat: If C3 remains low beyond 12 weeks, this is NOT typical APSGN and requires kidney biopsy to exclude C3 glomerulonephritis or other complement-mediated diseases 2. Normal C3 recovery within 6-8 weeks is expected in true APSGN 5.
High-degree proteinuria (≥2+) is significantly associated with elevated serum creatinine (>100 μmol/L) and may indicate more severe disease requiring closer monitoring 5. These patients are more likely to have atypical histological findings including crescents 5.
Prognosis
The prognosis is generally excellent with early diagnosis and supportive treatment 2. Most children experience complete recovery 1, 4. However, patients with crescentic GN or rapidly progressive disease require long-term monitoring of serum creatinine, urinalysis, and blood pressure 1.
Differential Considerations to Rule Out
Before finalizing the diagnosis, exclude 2:
- IgA nephropathy (can present similarly but different immunofluorescence pattern)
- ANCA-associated vasculitis (check ANCA if atypical features)
- Anti-GBM disease (check anti-GBM antibodies if rapidly progressive)
- Other infection-related GN (endocarditis, shunt nephritis - assess based on clinical context)