Inferior vena cava thrombosis as a possible cause of nephrotic-range proteinuria: two case reports.

Nephrotic-range proteinuria is a common reason for nephrological consultation in clinical practice. The differential diagnosis is wide, and generally focuses on different forms of glomerulonephritis, but other causes should not be overlooked, as illustrated in this article. We report two female patients with nephrotic-range proteinuria. In the first case, a 46 year old Caucasian patient who suffered from extreme obesity (Body mass index (BMI) 77 kg/m <sup>2</sup> ), acute kidney injury and nephrotic-range proteinuria were discovered during an emergency consultation for acute abdominal pain. The second patient (aged 52, also Caucasian) developed stage 4 chronic kidney disease and nephrotic proteinuria (protein/creatinine ratio 1821 g/mol) after accidental rupture of the inferior vena cava during a gastric bypass operation. On split-urine collection, both had a much higher degree of proteinuria during the day than during the night, compatible with orthostatic proteinuria. At further work-up, inferior vena cava thrombosis was diagnosed in both patients, whereas renal veins were patent. After simple anticoagulation in the first case, and anticoagulation plus endovascular recanalization in the second, there was almost complete resolution of the orthostatic proteinuria and a strong improvement of the estimated glomerular filtration rate in both patients. These cases highlight that nephrotic-range proteinuria can be linked to inferior vena cava thrombosis, and that a split-urine collection may also be very useful in the diagnostic work-up of proteinuria in adults