Plasma donors can give far more often than blood donors, and here is why
Whole blood donors wait 56 days between donations. Plasma donors can often return within a few days, giving up to a litre at a time. The trick is that the machine hands the red cells straight back, and the body rebuilds the missing plasma volume within about 24 hours.
Plasmapheresis means taking blood out of the body, separating off the plasma, the clear liquid the cells float in, and then treating, replacing or keeping it. Its name joins Greek words for something moulded and for taking away. It was first described in animal experiments by Vadim Yurevick and Nicolay Rosenberg in Saint Petersburg in 1913 and by John Abel and Leonard Rowntree at Johns Hopkins in 1914; human results from six plasma donors were reported in 1944.
Separation can be done in batches, with about 300 millilitres centrifuged at a time through a single line, by continuous centrifugation, or by filtering through dialysis equipment, which keeps less than 100 millilitres outside the body at once. Because blood in the circuit tends to clot, one common approach adds sodium citrate, which binds calcium. That works well but can push calcium dangerously low, so calcium is often given back during the procedure.
As a treatment, the aim is usually to clear harmful antibodies quickly in autoimmune conditions such as myasthenia gravis or Guillain-Barré syndrome. In plasma exchange the patient's plasma is thrown away and replaced, commonly with a mix of about 70 percent albumin and 30 percent saline. Exchange acts fast, but drugs that damp down antibody production are still needed for lasting control. The therapy is uncommon in the United States and used more in Europe and especially Japan.
Donation is mostly about manufacturing. Collected plasma is frozen below minus 20 degrees Celsius and fractionated into components such as albumin and immunoglobulins for medicines. Donors are screened at every visit, with HIV checked both by antibody tests and by nucleic acid methods that catch recent infections. The older manual method carried a real risk of returning the wrong red cells, so donors recited their names and ID numbers over the bags; automated machines have largely replaced it. In some countries, including the United States, Austria and Germany, donors are paid.
Source: Plasmapheresis
