A young man of East Asian descent presents with sudden gross hematuria 1-2 days after a viral URI with normal complement; most likely diagnosis?

• A. Berger disease
• B. Buerger disease
• C. Postinfectious glomerulonephritis
• D. Pseudoephedrine

Answer: (A)

The pattern being tested is IgA nephropathy (Berger disease): sudden gross hematuria that occurs soon after a mucosal infection, especially in young men, with normal complement levels. After a viral upper respiratory infection, an abnormal IgA immune response leads to deposition of IgA immune complexes in the glomerular mesangium, triggering hematuria that often appears within a day or two of the URI. The fact that the complement level is normal supports this diagnosis, because postinfectious glomerulonephritis typically shows reduced C3 due to immune-complex–mediated complement consumption and usually occurs 1–3 weeks after infection, not immediately after.

Other choices don’t fit this presentation as well: a vascular inflammatory disease affecting medium and small arteries would cause systemic vascular symptoms rather than isolated glomerular bleeding; a postinfectious glomerulonephritis would fit timing and complement findings but the delayed onset after infection and demographic pattern are less typical; a drug like pseudoephedrine isn’t a disease causing sudden gross hematuria in this context.