Patients with nephrotic syndrome are at increased risk for lower extremity, pulmonary, and renal vein thromboses (see Plate 4-35) because of urinary losses of anticoagulant proteins, such as antithrombin and plasminogen, as well as increased hepatic production of procoagulant proteins, such as fibrinogen and other clotting factors. Among the nephrotic syndromes, thromboses are most often seen in patients with membranous nephropathy, but any patient with proteinuria above 10 g/day and albumin levels below 2 g/dL should be considered at risk.