Why/how does a clot form in a fistula? Is there any way to avoid it?

Hi Jane,

You might benefit from reading the Vascular Access module of the Core Curriculum for the Dialysis Technician (you can download it from the MEI website –, which has a good explanation of this with some illustrations that may help you understand it better.

Blood vessels are lined with a smooth tissue called intima that allows blood cells to flow by without snagging. Because a fistula (or graft) has anastomoses–spots where the vessels were sewn together–the intima is already disturbed, and there is a built-in risk for clotting. Plus, each needle stick creates a tiny point of damage (more so if the needles are placed against the flow of blood).

Any time there is damage to the body (intima or elsewhere), white blood cells are attracted to the site. A network of fibrin forms to trap the white blood cells and hold them in place so they can do their job. This fibrin net also catches red blood cells.

If blood flow slows down inside the fistula–such as from an episode of low blood pressure–it creates a chance for this healing process to occur. Unfortunately, a side effect can be a clot.

How to avoid it?
1). Place both fistula needles antegrade (with the flow of blood) NOT retrograde (against it)
2). Do a type of dialysis–like daily or nocturnal–that make episodes of low blood pressure much less likely
3). Don’t squeeze your fistula arm; it could slow blood flow through

TY I will check it out.