can be collected by similar methods. these products generally have the same shelf life and storage conditions as their conventionally-produced counterparts. donors are sometimes paid; in the u.s. and europe, most blood for transfusion is collected from volunteers while plasma for other purposes may be from paid donors. most collection facilities as well as hospital blood banks also perform testing to determine the blood type of patients and to identify compatible blood products, along with a battery of tests (e.g. disease) and treatments (e.g. leukocyte filtration) to ensure or enhance quality. the increasingly recognized problem of inadequate efficacy of transfusion is also raising the profile of rbc viability and quality. notably, u.s. hospitals spend more on dealing with the consequences of transfusion-related complications than on the combined costs of buying, testing/treating, and transfusing their blood. storage and management whole blood is often separated, using a centrifuge, into components for storage and transportation. routine blood storage is 42 days or 6 weeks for stored packed red blood cells (also called "strbc" or "prbc"), by far the most commonly transfused blood product, and involves refrigeration but usually not freezing. there has been increasing controversy about whether a given product unit's age is a factor in transfusion efficacy, specifically on whether "older" blood directly or indirectly increases risks of complications. studies have not been consistent on answering this question, with some showing that older blood is indeed less effective but with others showing no such difference; nevertheless, as storage time remains the only available way to estimate quality status or loss, a first-in-first-out inventory management approach is standard presently. it is also important to consider that there is large variability in storage results for different donors, which combined with limited available quality testing, poses challenges to clinicians and regulators seeking reliable indicators of quality for blood products and storage systems. transfusions of platelets are comparatively far less numerous, but they present unique storage/management issues. platelets may only be stored for 7 days, due largely to their greater potential for contamination, which is in turn due largely to a higher storage temperature. rbc storage lesion insufficient transfusion efficacy can result from red blood cell (rbc) blood product units damaged by so-called storage lesion—a set of biochemical and biomechanical changes which occur during storage. with red cells, this can decrease viability and ability for tissue oxygenation. although some of the biochemical changes are reversible after the blood is transfused, the biomechanical changes are less so, and rejuvenation products are not yet able to adequately reverse this phenomenon. current regulatory measures are in place to minimize rbc storage lesion—including a maximum shelf life (currently 42 days), a maximum auto-hemolysis threshold (currently 1% in the us), and a minimum level of post-transfusion rbc survival in vivo (currently 75% after 24 hours). however, all of these criteria are applied in a universal manner that does not account for differences among units of product; for example, testing for the post-transfusion rbc survival in vivo is done on a sample of healthy volunteers, and then compliance is presumed for all rbc units based on universal (gmp) processing standards. rbc survival does not guarantee efficacy, but it is a necessary prerequisite for cell function, and hence serves as a regulatory proxy. opinions vary as to the best way to determine transfusion efficacy in a patient in vivo. in general, there are not yet any in vitro tests to assess quality deterioration or preservation for specific units of rbc blood product prior to their transfusion, though there is exploration of potentially relevant tests based on rbc membrane properties such as erythrocyte deformability and erythrocyte fragility (mechanical). many physicians have adopted a so-called "restrictive protocol"—whereby transfusion is held to a minimum—due in part to the noted uncertainties surrounding storage lesion, in addition to the very high direct and indirect costs of transfusions, along with the increasing view that many transfusions are inappropriate or use too many rbc units. platelet storage lesion platelet storage lesion is a very different phenomenon from rbc storage lesion, due largely to the different functions of the products and purposes of the respective transfusions, along with different processing issues and inventory management considerations. alternative inventory and release practices although as noted the primary inventory-management approach is first in, first out (fifo) to minimize product expiration, there are some deviations from this policy—both in current practice as well as under research. for example, exchange transfusion of rbc in neonates calls for use of blood product that is five days old or less, to "ensure" optimal cell function. also, some hospital blood banks will attempt to accommodate physicians' requests to provide low-aged rbc product for certain kinds of patients (e.g. cardiac surgery). more recently, novel approaches are being explored to complement or replace fifo. one is to balance the desire to reduce average product age (at transfusion) with the need to maintain sufficient availability of non-outdated product, leading to a strategic blend of fifo with last in, first out (lifo). long-term storage "long-term" storage for all blood products is relatively uncommon, compared to routine/short-term storage. cryopreservation of red blood cells is done to store rare units for up to ten years. the cells are incubated in a glycerol solution which acts as a cryoprotectant ("antifreeze") within the cells. the units are then placed in special sterile containers in a freezer at very low temperatures. the exact temperature depends on the glycerol concentration.