A 46-year-old man with biopsy-proven primary membranous nephropathy (proteinuria 9 g/day, serum albumin 2.1 g/dL) suddenly develops left flank pain and gross haematuria. Doppler ultrasound shows absence of flow in the left renal vein. What is the most likely explanation for this complication?

• A Loss of antithrombin III and other anticoagulant proteins in urine ✓
• B Direct invasion of the renal vein by immune deposits
• C Reactive thrombocytosis secondary to hypoalbuminaemia
• D Activation of protein C by circulating PLA2R antibodies

Explanation

Nephrotic syndrome causes a hypercoagulable state because anticoagulant proteins (antithrombin III, protein C, protein S) are lost in urine while hepatic fibrinogen synthesis increases. Renal vein thrombosis is the classic complication and occurs most often in membranous nephropathy. Prophylactic anticoagulation is considered when albumin falls below about 2.5 g/dL. The other options describe mechanisms that do not operate in this setting.

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.