<P> Platelets are either isolated from collected units of whole blood and pooled to make a therapeutic dose, or collected by platelet apheresis: blood is taken from the donor, passed through a device which removes the platelets, and the remainder is returned to the donor in a closed loop . The industry standard is for platelets to be tested for bacteria before transfusion to avoid septic reactions, which can be fatal . Recently the AABB Industry Standards for Blood Banks and Transfusion Services (5.1. 5.1) has allowed for use of pathogen reduction technology as an alternative to bacterial screenings in platelets . </P> <P> Pooled whole - blood platelets, sometimes called "random" platelets, are separated by one of two methods . In the US, a unit of whole blood is placed into a large centrifuge in what is referred to as a "soft spin ." At these settings, the platelets remain suspended in the plasma . The platelet - rich plasma (PRP) is removed from the red cells, then centrifuged at a faster setting to harvest the platelets from the plasma . In other regions of the world, the unit of whole blood is centrifuged using settings that cause the platelets to become suspended in the "buffy coat" layer, which includes the platelets and the white blood cells . The "buffy coat" is isolated in a sterile bag, suspended in a small amount of red blood cells and plasma, then centrifuged again to separate the platelets and plasma from the red and white blood cells . Regardless of the initial method of preparation, multiple donations may be combined into one container using a sterile connection device to manufacture a single product with the desired therapeutic dose . </P> <P> Apheresis platelets are collected using a mechanical device that draws blood from the donor and centrifuges the collected blood to separate out the platelets and other components to be collected . The remaining blood is returned to the donor . The advantage to this method is that a single donation provides at least one therapeutic dose, as opposed to the multiple donations for whole - blood platelets . This means that a recipient is not exposed to as many different donors and has less risk of transfusion - transmitted disease and other complications . Sometimes a person such as a cancer patient who requires routine transfusions of platelets will receive repeated donations from a specific donor to further minimize the risk . Pathogen reduction of platelets using for example, riboflavin and UV light treatments can also be carried out to reduce the infectious load of pathogens contained in donated blood products, thereby reducing the risk of transmission of transfusion transmitted diseases . Another photochemical treatment process utilizing amotosalen and UVA light has been developed for the inactivation of viruses, bacteria, parasites, and leukocytes that can contaminate blood components intended for transfusion . In addition, apheresis platelets tend to contain fewer contaminating red blood cells because the collection method is more efficient than "soft spin" centrifugation at isolating the desired blood component . </P> <P> Platelets collected by either method have a very short shelf life, typically five days . This results in frequent problems with short supply, as testing the donations often requires up to a full day . Since there are no effective preservative solutions for platelets, they lose potency quickly and are best when fresh . </P>

Which of the following plasma proteins is(are) required for the formation of a platelet plug