A 42-year-old man presents with acute kidney injury (creatinine 4.2 mg/dL, baseline 0.9 mg/dL over 10 days), hematuria with dysmorphic red blood cells and RBC casts, and hypertension. Renal biopsy shows the pathologic findings illustrated in the diagram. The structure marked **A** is identified on light microscopy in >50% of glomeruli. Which of the following clinical features is MOST consistent with the pathologic finding at **A** and its underlying pathogenesis?

Explanation

## Why "Rapid decline in GFR (≥50% within days to weeks)..." is right The structure marked **A** — cellular crescents in Bowman space — is the pathologic hallmark of rapidly progressive glomerulonephritis (RPGN) / crescentic glomerulonephritis. By definition, RPGN is characterized by severe glomerular capillary injury with rupture of the capillary wall, allowing fibrin and inflammatory cells to leak into Bowman space. Proliferation of parietal epithelial cells, macrophages, and fibroblasts forms a cellular crescent that physically compresses the glomerular tuft and obliterates the urinary space, resulting in rapid loss of renal function (≥50% decline in GFR within days to weeks). This is the defining clinicopathologic syndrome. The patient's presentation (AKI with creatinine rise from 0.9 to 4.2 in 10 days, dysmorphic hematuria, RBC casts) is pathognomonic for RPGN, and the biopsy finding of cellular crescents in >50% of glomeruli confirms the diagnosis. ## Why each distractor is wrong - **Gradual proteinuria and hematuria over months...**: This describes a chronic glomerulonephritis (e.g., membranoproliferative GN or chronic IgA nephropathy), not RPGN. Cellular crescents cause acute, fulminant renal failure, not gradual decline. The timeline contradicts the anchor. - **Nephrotic-range proteinuria (>3.5 g/day)...**: While RPGN can present with proteinuria, it is typically sub-nephrotic (<3 g/day). Nephrotic-range proteinuria with selective proteinuria and foot process effacement is characteristic of minimal change disease or focal segmental glomerulosclerosis, not crescentic GN. Cellular crescents do not cause podocyte foot process effacement as their primary mechanism. - **Asymptomatic microscopic hematuria with normal renal function...**: This describes IgA nephropathy (structure **D** in the diagram — mesangial IgA deposition). IgA nephropathy typically has an indolent course with preserved renal function unless it progresses to crescentic IgA nephropathy. Cellular crescents in >50% of glomeruli would cause rapid renal dysfunction, not normal renal function. **High-Yield:** Cellular crescents = RPGN = rapid GFR decline (days to weeks) + nephritic syndrome (hematuria, RBC casts, hypertension); pathogenesis is capillary rupture → crescent formation → tuft compression and urinary space obliteration. [cite: Robbins 10e Ch 20; Harrison 21e Ch 314]