After a short physical examination, the donor is taken into the donation room and sits in a chair next to the machine. The technician cleans one or both arms with iodine, or other disinfectant, and inserts the catheter into a vein in the arm. With some procedures both arms are used, one to draw blood and the other to return it. The process takes about one to two hours while blood is pulled into the machine, mixed with an anticoagulant such as sodium citrate, spun around, and returned to the donor. "Double needle" procedures using both arms tend to be shorter since the blood is drawn and returned through different catheters; with "single needle" procedures a set volume is drawn and processed in the first part of the cycle and returned in the second part. The donor's blood undergoes repeated cycles of draw and return.