During this process, your blood will flow into the machine and then directly back into your bloodstream through the second line. Blood will be drawn from 1 arm through a catheter (needle and tube) connected to the leukapheresis machine. Inside the machine, the white blood cells will be separated from the rest of the blood cells and collected in a sterile bag. Then, the rest of the blood cells will be returned through a catheter to your other arm. A blood thinner called citrate will be added to the blood as it enters the machine in order to lower the risk of your blood clotting in the machine.