Master USMLE Podcast – IgA Nephropathy: A High-Yield Case

A 22-year-old male wakes up in the morning and notices his urine is dark-colored. No pain. No fever. No dysuria. Just tea-colored urine. He recently had a mild sore throat and nasal congestion a few days ago. No antibiotics. Just ibuprofen as needed. No history of kidney disease. No significant past medical history. Blood Pressure: 145/90 mmHg Heart Rate: 80/min Temperature: 37.7°C (99.9°F) Respiratory Rate: 14/min No periorbital edema No rash or joint pain No tenderness on abdominal or flank palpation Hematuria (Large blood on dipstick, >50 RBCs per high-power field) Proteinuria (1+) RBC Casts: Present Serum Creatinine: 1.4 mg/dL (Mildly elevated) Blood Urea Nitrogen (BUN): Normal Complement Levels (C3, C4): Normal This is glomerular hematuria, not a lower urinary tract issue. The presence of RBC casts and proteinuria confirms glomerular involvement. Two diagnoses need to be considered: Appears 1-3 weeks after a Group A Strep infection Low C3 complement Periorbital edema, hypertension, and cola-colored urine Subepithelial immune complex deposits ("humps") on kidney biopsy Appears within days of an upper respiratory infection Normal complement levels (C3, C4) Recurrent episodes of gross hematuria Mild hypertension Mesangial IgA deposition on kidney biopsy Key Differentiation: If hematuria occurs within days of an upper respiratory infection and complement levels are normal, IgA nephropathy is the most likely diagnosis. IgA nephropathy is the most common primary glomerulonephritis worldwide, caused by IgA immune complex deposition in the mesangium, leading to inflammation and glomerular damage. Risk Factors for Progression to CKD: Persistent proteinuria (>1 g/day) Uncontrolled hypertension Progressive increase in serum creatinine Most cases remain stable, but some progress to end-stage renal disease (ESRD). Urinalysis → Proteinuria, hematuria, RBC casts Serum Creatinine → Elevated in progressive disease Complement Levels (C3, C4) → Normal in IgA nephropathy Definitive Test: Kidney Biopsy Mnemonic: "IgA – Immediate Gross hematuria After infection." ACE inhibitors or ARBs – Reduce proteinuria and control BP Supportive care – Monitor kidney function Corticosteroids – Reduce mesangial inflammation Immunosuppressants – In select cases Dialysis Kidney transplant (IgA nephropathy may recur post-transplant) A 20-year-old male presents with recurrent episodes of gross hematuria that begin a day or two after viral infections. Proteinuria: 1+ RBC casts present C3 and C4 complement levels: Normal Which of the following is the most likely diagnosis? A) Subepithelial immune complex deposits B) Mesangial IgA deposition C) Linear IgG deposition along the glomerular basement membrane D) Fibrin deposits with crescent formation