Cumulative incidence of venous thrombosis in 163 patients with PNH clones. The 10-year cumulative incidence of thrombosis in the whole group of 163 patients was 23%. This includes patients on primary thromboprophylaxis with warfarin. The curve starts at 5.4%, reflecting the incidence of patients presenting with thrombotic events. One episode of hepatic vein thrombosis was excluded from the analysis because when the diagnosis was established by abdominal ultrasound scan it was clearly extremely longstanding (probably years previously) and an accurate estimate of the timing of thrombosis could not be made.