- Apheresis. Whole blood is collected through an arm vein (similar to donating blood), and circulated through a cell separator machine, where it is spun to separate the components. The red cells are then returned to the patient either through the same needle or through a needle in the other arm, and the plasma and white cells are extracted for study. The procedure, which takes 1 to 2 hours, may be repeated up to 3 times.