During the actual blood donation process, your blood is drawn through a needle placed in a vein in one arm. A special machine separates the plasma and often the platelets from your blood sample. This process is called plasmapheresis. The remaining red blood cells and other blood components are then returned to your body, along with a little saline (salt) solution.
People with the blood type AB are in the greatest demand for plasma donation. They make up just 2 in 50 people, their plasma is universal. This means their plasma can be used by anyone. People can donate plasma every 28 days, up to 13 times a year.