glycerol or other cryoprotectants, rbcs can be frozen and thus stored for much longer (this is not common). frozen rbcs are typically assigned a ten-year expiration date, though older units have been transfused successfully. the freezing process is expensive and time-consuming and is generally reserved for rare units such as ones that can be used in patients that have unusual antibodies. since frozen rbcs have glycerol added, the added glycerol must be removed by washing the red blood cells using special equipment, such as the ibm 2991 cell processor in a similar manner to washing rbcs. the processing (often termed "manufacture", since the result is deemed a biologic biopharmaceutical product) and the storage can occur at a collection center or a blood bank. rbcs are mixed with an anticoagulant and storage solution which provides nutrients and aims to preserve viability and functionality of the cells (limiting their so-called "storage lesion"), which are stored at refrigerated temperatures for up to 42 days (in the us), except for the rather unusual long-term storage in which case they can be frozen for up to 10 years. the cells are separated from the fluid portion of the blood after it is collected from a donor, or during the collection process in the case of apheresis. the product is then sometimes modified after collection to meet specific patient requirements. red blood cell rejuvenation is a method to increase levels of 2,3-diphosphoglycerate (2,3-dpg) and atp in stored prbc. this process requires incubating the packed red blood cells with a rejuvenation solution and subsequent washing. for a particular combination of preservation fluid and rejuvenation solution, the fda allows prbc up to 3 days past the 42-day expiration period to be rejuvenated and used. 2,3-dpg levels in prbc greatly affects oxygen-release characteristics. society and culture economics in the united kingdom they cost about £120 per unit. names the product is typically abbreviated rbc, prbc, prbc, and sometimes strbc or even lrbc (the latter being to indicate those that have been leukoreduced, which is now true for the vast majority of rbc units). the name "red blood cells" with initial capitals indicates a standardized blood product in the united states. without capitalization, it is simply generic without specifying whether or not the cells comprise a blood product, patient blood, etc. (with other generic terms for it being "erythrocyte" and "red cell").