Final answer:
The shelf life of stored blood is extended with nutrient supplements and controlled freezing with protectants such as glycerol. The blood is cooled slowly and stored at ultra-low temperatures.
Step-by-step explanation:
The shelf life of stored blood is extended primarily through the addition of nutrient supplements, not by repeated freezing and thawing, inverted storage freezers, or constant centrifugation. These nutrient supplements provide the energy source necessary for the preservation of blood during storage. It's also crucial to maintain blood at low temperatures to ensure long-term storage and post-preparative stability.
While freezing is a common method to preserve biological materials, the process for blood is carefully controlled to avoid damage to the cells. Typically, a protectant such as glycerol is used in conjunction with a slow cooling process before storage at ultra-low temperatures, which can be as low as -196°C when liquid nitrogen is used.