To reduce red blood cell (RBC) exposure to uncontrolled temperatures during storage and transit, a 30-minute rule was devised. Furthermore, RBC units provided for transfusion should not be kept at room temperature (RT) for longer than 4 hours (4-hour rule). This allows time for the donor unit to arrive at the hospital transfusion service and be processed into its final product form. In general, RBCs stored in additive solutions can be maintained at room temperature for up to 24 hours after removal from the refrigerator. The actual length of time that they will remain viable is dependent on many factors, such as the type of operation performed, the age and health of the patient, and the specific RBCs being transfused. For example, patients who undergo major surgery where large volumes of RBCs are needed in a short period of time may need RBCs that are stable at room temperature for an extended period of time (e.g., up to 72 hours). In this case, it may be necessary to store the RBCs at colder temperatures until they are needed for treatment. The ability of RBCs to remain intact and function properly after being frozen or cooled and then subsequently thawed and refrozen depends on the method used to preserve them during transportation and storage.