Reasons for dialysis circuit clotting

We want to learn why and how some people on dialysis form blood clots in the dialysis machine or in their fistula. Most patients on dialysis receive a blood thinner called heparin to prevent these clots, but heparin can sometimes cause bleeding. We would like to know if safer medications could work in preventing these clots. This study is only about learning more information from blood samples and does not involve treatment.