 - Automated pheresis Blood is drawn through a needle placed in an arm vein and circulated through a cell separator machine. The plasma liquid part of the blood and white cells are extracted, and the red cells are re-infused into the donor through the same needle or a needle in the other arm. An anticoagulant medication to prevent blood from clotting is usually added to the blood while in the machine to prevent it from clotting during processing. 