Plasmapheresis is a process in which the liquid part of the blood, or plasma, is separated from the blood cells. Typically, the plasma is replaced with another solution such as saline or albumin, or the plasma is treated and then returned to your body. If you’re sick, your plasma can contain antibodies that attack the immune system. A machine can be used to remove the affected plasma and replace it with good plasma or a plasma substitute. This is also known as plasma exchange. The process is similar to kidney dialysis. Plasmapheresis also can refer to the plasma donation process, where the plasma is removed and the blood cells are returned to your body.