Renal Vein Thrombosis

Renal vein thrombosis is thrombus formation in one or both renal veins, which may extend into the inferior vena cava.

• Causes: nephrotic syndrome (especially membranous nephropathy, with serum albumin below 25 g/L), renal cell carcinoma (tumour thrombus), hypercoagulable states (antiphospholipid syndrome, inherited thrombophilia, oral contraceptives, pregnancy and puerperium), trauma, dehydration in neonates and infants, renal transplantation, and surgical complications.
• Neonates and infants are affected with dehydration, sepsis and maternal diabetes; adults mainly with nephrotic syndrome.
• Chronic thrombosis may be silent, discovered by pulmonary embolism or incidental imaging.

Acute: flank pain, haematuria, fever, nausea, an enlarged tender kidney, oliguria, acute kidney injury, sudden worsening of proteinuria.

• Chronic: often silent; proteinuria, collateral venous circulation, slowly deteriorating function; pulmonary embolism may be the first sign.
• Infants: haematuria, palpable flank mass, thrombocytopenia, hypertension, renal failure.
• Differential diagnosis: renal colic, pyelonephritis, renal infarction, renal tumour, nephrotic syndrome progression, glomerulonephritis, renal arterial thrombosis.
• Complications: pulmonary embolism, acute kidney injury, kidney infarction and atrophy, renovascular hypertension, extension into the inferior vena cava, chronic kidney disease and death.

Creatinine, urea, electrolytes, urinalysis (haematuria, proteinuria), albumin, lipids, full blood count, coagulation, D-dimer (nonspecific), antithrombin level, antiphospholipid antibodies, thrombophilia tests, lactate dehydrogenase.

• Doppler ultrasound shows enlarged kidney, absent venous flow and echogenic thrombus; contrast-enhanced CT venography (filling defect, enlarged kidney, delayed nephrogram) or magnetic resonance venography are definitive; renal venography is reserved for interventions.
• Evaluate for renal cell carcinoma (CT chest, abdomen and pelvis), nephrotic syndrome cause (kidney biopsy), pulmonary embolism with CT pulmonary angiography when symptoms.

Supportive: hydration, analgesia, treat the underlying cause (nephrotic syndrome, dehydration, sepsis), blood pressure control, avoid diuretic excess in nephrotic patients.

Pharmacological

• Anticoagulation for all symptomatic or extending thrombi: enoxaparin 1 mg/kg twice daily (1.5 mg/kg daily; reduce to 1 mg/kg daily if creatinine clearance is below 30 mL/min) or unfractionated heparin 80 units/kg bolus then 18 units/kg/h; transition to warfarin (INR 2 to 3) for at least 3 to 6 months, or a direct oral anticoagulant (rivaroxaban 15 mg twice daily for 21 days then 20 mg daily, or apixaban 10 mg twice daily for 7 days then 5 mg twice daily) in patients with preserved function.
• Continue anticoagulation for as long as the nephrotic syndrome is active (albumin below 25 g/L) or the risk factor persists; indefinite for recurrent or unprovoked events.
• Prophylactic anticoagulation in membranous nephropathy with serum albumin below 25 g/L and low bleeding risk (enoxaparin 40 mg daily, or warfarin).
• Neonates: enoxaparin 1.5 mg/kg twice daily (preterm 2 mg/kg twice daily) titrated to anti-Xa 0.5 to 1.0 units/mL, for 6 weeks to 3 months; unfractionated heparin for the first days if renal failure.
• Nephrotic syndrome: corticosteroids and immunosuppression by cause (prednisolone 1 mg/kg daily for minimal change disease).
• Catheter-directed thrombolysis (alteplase) in bilateral thrombosis with acute kidney injury or thrombus extension if bleeding risk is acceptable.

Procedures: percutaneous mechanical thrombectomy; surgical thrombectomy or nephrectomy for tumour thrombus (renal cell carcinoma); inferior vena cava filter if anticoagulation is contraindicated and pulmonary embolism is a risk.

Special groups: pregnancy (low molecular weight heparin, avoid warfarin and direct anticoagulants), neonates (specialist care), antiphospholipid syndrome (warfarin, not direct oral anticoagulants).

Red flags: pulmonary embolism, bilateral thrombosis with oliguria, inferior vena cava extension, bleeding on anticoagulation.

Follow-up: imaging at 3 months; kidney function and proteinuria; review anticoagulation at 3 and 6 months; platelet and renal checks on heparin.