Why would someone blood clog a dialysis machine?

See below: Dialysis involves the patients blood to run against the dialysis fluids in a artificial kidney or dialyser, both have seperate circuits and the blood ciruit may clot and block the circuit.The reasons are because it is running externally through a plastic. Many times a anticoagulant like Heparin is mixed with the blood artificially to prevent it clotting.

Flow rate?: Blood may clot in the dialysis circuit if it isn't flowing fast enough. Blood has a tendency to clot if it 'stands still' or slows down enough. The quality of the 'access' ( i.e., usually a fistula) may be a factor here. Additionally, the position of the needles within the fistula may also impact the flow rate. And needless to say, a crimped line will result in clotting if not corrected. Lgromkomd.