A 40-year-old woman known to have biopsy proven membranous nephropathy develops sudden left flank pain, gross hematuria, and a fall in urine output. Contrast CT shows a filling defect extending into the left renal vein. What is the most likely underlying mechanism of her baseline disease that predisposed her to this event?
- A Loss of antithrombin III in urine producing a hypercoagulable state ✓
- B Direct invasion of the renal vein by subepithelial immune complexes
- C Granulomatous inflammation of the renal venous wall
- D Activation of the contact pathway by free hemoglobin
Correct answer: A. Loss of antithrombin III in urine producing a hypercoagulable state
Explanation
Urinary loss of antithrombin III along with other small proteins creates a hypercoagulable state in nephrotic syndrome, and membranous nephropathy carries the highest reported risk of renal vein thrombosis among the glomerular diseases. The presentation of flank pain, hematuria, and falling output in a nephrotic patient should prompt imaging for this complication. Immune complexes do not invade veins, making the other options mechanistically implausible.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.