DefinitionRenal vein thrombosis is a blood clot that develops in the vein that drains blood from the kidney.Alternative NamesClot in the renal vein; Occlusion - renal veinCauses, incidence, and risk factorsRenal vein thrombosis is a fairly uncommon situation that may happen after trauma to the abdomen or back, or it may occur due to:Scar formationStrictureTumorIt may be associated with nephrotic syndrome.In some children, it occurs after severe dehydration and is a more serious condition than in adults. Dehydration is the most common cause of renal vein thrombosis in infants.SymptomsBloody urineDecreased urine outputFlank pain or low Back painSigns and testsAn examination may not reveal the specific problem, but may indicate nephrotic syndrome or other causes of renal vein thrombosis.Abdom