Acute Post-Streptococcal Glomerulonephritis (APSGN)
In a patient presenting with facial (especially periorbital) edema 1–3 weeks after a streptococcal infection, you should strongly suspect acute post-streptococcal glomerulonephritis and immediately initiate a focused diagnostic workup including urinalysis, serum complement levels, and streptococcal antibody titers. 1, 2
Clinical Presentation and Timing
The hallmark latency period is critical for diagnosis:
- 1–2 weeks after pharyngeal streptococcal infection 3
- 2–6 weeks after skin infection (impetigo) 3
- Concurrent infectious and nephritis symptoms should raise suspicion for alternative diagnoses, not APSGN 3
The classic presentation includes:
- Periorbital or facial edema (often the presenting complaint) 1, 2, 4
- Tea-colored or cola-colored urine (gross hematuria) 2, 4
- Hypertension 2, 5, 3
- Oliguria in severe cases 2
Essential Diagnostic Workup
First-Line Laboratory Tests (Order Immediately):
Urinalysis with microscopy:
- Hematuria (microscopic or gross) 2, 5, 3
- Proteinuria (may range from mild to nephrotic-range) 2, 3
- Red blood cell casts (highly specific for glomerulonephritis) 2
Serum complement levels:
- Low C3 level (present in >90% of APSGN cases and typically appears earlier than antibody titers) 3
- Normal or mildly decreased C4 (helps differentiate from other causes of glomerulonephritis) 3
- C3 typically normalizes within 6–8 weeks; persistent hypocomplementemia beyond 8–12 weeks suggests alternative diagnosis 1, 2
Streptococcal antibody titers:
- Antistreptolysin O (ASO) titer (elevated in pharyngeal infections) 5, 4
- Anti-DNAase B titer (more sensitive for skin infections) 5
- At least one should be elevated to support the diagnosis 1, 5
Renal function tests:
- Serum creatinine and BUN (assess for acute kidney injury) 2, 3
- Electrolytes, particularly potassium (risk of hyperkalemia) 3
Additional Workup:
Blood pressure measurement (essential, as hypertension is common and may be severe) 2, 3
Complete blood count (may show mild anemia) 4
Throat or skin culture (if active infection suspected, though often negative by time of presentation) 1
When to Consider Renal Biopsy
Kidney biopsy is not routinely required for typical APSGN but should be strongly considered in: 1, 2
- Diagnostic uncertainty (atypical presentation or course) 2
- Rapidly progressive glomerulonephritis with crescents 1, 2
- Persistent hypocomplementemia beyond 8–12 weeks 1
- Severe acute kidney injury requiring dialysis 2
- Adults (who have higher risk of progression to chronic kidney disease) 5, 6
Critical Pitfalls to Avoid
Do not delay workup waiting for streptococcal culture results, as the infection is often resolved by the time nephritis presents 1, 3
Do not assume normal complement rules out APSGN, though low C3 is present in >90% of cases 3
Do not overlook hypertensive emergencies or congestive heart failure, which require immediate intervention and represent the most dangerous complications in the first 7–10 days 2, 3
Recognize that children under 3 years rarely develop APSGN due to immature immune systems, so consider alternative diagnoses more strongly in this age group 4
Antibiotic Treatment Considerations
Even if the streptococcal infection has clinically resolved, treat with penicillin (or erythromycin if penicillin-allergic) to decrease antigenic load, though this does not prevent glomerulonephritis once it has developed 1
The guideline recommendation is clear: appropriate treatment of the infectious disease is suggested, but antibiotics do not alter the course of established APSGN 1
Age-Related Prognostic Differences
Children: Excellent prognosis with complete recovery in >90% of cases; persistent microscopic hematuria or proteinuria in <10% 3
Adults: Higher incidence of progression to hypertension and chronic renal failure, with incomplete histological resolution possible even years later 5, 6