Platelet Collection
The separation of individual blood components is done with a specialized centrifuge (see apheresis). The earliest manual forms of thrombapheresis are done by the separation of platelets from multiple bags of whole blood collected from donors or blood sellers. Since each blood bag (usually 250 mL or 500 mL) contains a relatively small number of platelets, it can take as many as a dozen blood bags (usually from 5 to 10 bags, depending on the size of the blood bags and each donor's platelet count) to accumulate a single unit of platelets (enough for one patient). This greatly increases the risks of the transfusion. Each unit of platelets separated from donated whole blood is called a "platelet concentrate".
Modern automatic thrombapheresis allows blood donors to give a portion of their platelets, while keeping their red blood cells and at least a portion of blood plasma. Therefore, no more than three units of platelets are generally harvested in any one sitting from a donor. Most donors will donate a "single" or "double" unit, however the occurrence of "triples" has been increasing as more suitable donors are recruited.
Because platelets have a shelf life of just 5 days, more platelet donors are always needed. Some centers are experimenting with 7 day platelets, but this requires additional testing and the lack of any preservative solutions means that the product is far more effective when fresh.
Even though red blood cells can also be collected in the process, most blood donation organizations do not do so because it takes much longer for the human body to replenish their loss. If the donor donates both red blood cells and platelets, it takes months, rather than days or weeks, before they are allowed to donate again (the guidelines regarding blood donation intervals are country-specific).
In most cases, blood plasma is returned to the donor as well. However, in locations that have plasma processing facilities, a part of the donor's plasma can also be collected in a separate blood bag (see plasmapheresis).
Read more about this topic: Plateletpheresis
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