A 28-year-old male from rural India presents with a 10-day history of cola-coloured urine, facial puffiness, and mild dyspnea on exertion. He reports a sore throat 2 weeks prior that resolved spontaneously. On examination: BP 148/94 mmHg, mild periorbital edema, normal heart sounds. Urinalysis shows 3+ protein, RBC casts, and dysmorphic RBCs. Serum creatinine is 1.8 mg/dL (baseline ~0.9), and complement C3 is normal. Anti-streptolysin O (ASO) titre is elevated at 1:640. What is the most likely diagnosis?

Explanation

## Diagnosis: Post-Streptococcal Glomerulonephritis (PSGN) ### Clinical Presentation **Key Point:** PSGN is the most common nephritic syndrome in children and young adults worldwide, particularly in resource-limited settings. The vignette contains the classic triad: 1. **Preceding streptococcal infection** — sore throat 2 weeks prior (latency period 7–14 days post-pharyngitis, 3–6 weeks post-skin infection) 2. **Acute nephritic syndrome** — cola-coloured urine (haematuria), hypertension, oedema, dyspnea (fluid overload) 3. **Serological confirmation** — elevated ASO titre (anti-streptolysin O antibody) ### Laboratory Features | Feature | PSGN | IgAN | Lupus | MPGN-1 | |---------|------|------|-------|--------| | **RBC casts** | Present | Present | Present | Rare | | **C3 level** | ↓ (50–80% of cases) | Normal | ↓ | ↓ | | **ASO titre** | ↑ | Normal | Normal | Normal | | **ANA** | Negative | Negative | ↑ | Negative | | **Latency after infection** | 1–3 weeks (throat) | None | None | None | **High-Yield:** Normal C3 does NOT exclude PSGN — up to 20% of cases have normal complement levels. The ASO titre and clinical history are diagnostic. ### Why This Is PSGN - **Temporal relationship** — 2-week interval between pharyngitis and renal disease - **ASO titre elevation** — confirms recent streptococcal infection - **Acute nephritic presentation** — hypertension, haematuria, RBC casts, rising creatinine - **Age and geography** — common in young adults in endemic areas ### Prognosis & Management **Clinical Pearl:** Most children with PSGN recover spontaneously; adults have a worse prognosis with ~10% developing chronic kidney disease. 1. **Supportive care** — fluid restriction, salt restriction, diuretics for oedema/hypertension 2. **Antihypertensives** — ACE inhibitors (renal protective) 3. **Antibiotics** — penicillin V to eradicate residual streptococci 4. **Immunosuppression** — NOT indicated for uncomplicated PSGN; reserved for rapidly progressive GN or severe crescentic disease **Mnemonic: PSGN Diagnosis — SOAP** - **S**treptococcal infection (recent) - **O**edema, hypertension, oliguria - **A**SO titre elevated - **P**rotein + RBC casts on UA ### Differential Exclusion - **IgA nephropathy:** No preceding infection, normal ASO titre, often recurrent haematuria - **Lupus nephritis:** Requires positive ANA, anti-dsDNA; systemic features (rash, arthritis, serositis) - **MPGN-1:** Insidious onset, no clear infectious trigger, persistent C3 depression [cite:Harrison 21e Ch 279]