It is likely that the 30 minute rule originated as a result of the 1971 publication of Pick and Fabijanic¹ who investigated the time taken for a unit of cooled blood to reach 10 °C when removed from the refrigerator. They found that, whether the unit was handled or not, the surface temperature reached 10 °C between 15 and 30 minutes after removal into ambient conditions, whereas the core temperature took 45 to 60 minutes to reach 10 °C . Thirty minutes thus would appear to be a reasonable cut-off to ensure that the core temperature did not rise above 10 °C.
It is not clear why Pick and Fabijanic chose 10 °C as the upper limit, it may have been on the basis of data published by Hughes-Jones² that showed reduced, but acceptable, recovery of red cells following transfusion when stored at 10 °C for 34 days. In addition, 10 ºC may have been chosen as a practical limit based on the wet ice type of transit containers that were available at that time. The relevance of short-term exposures to 10 °C, and thus the relevance of the 30 minute rule, is therefore worthy of review.
If a patient is not ready to receive a planned transfusion, and red cells are out of controlled storage for more than 30 minutes they cannot be returned to stock for issue to that or another patient. Furthermore, red cells sent to a location remote from a blood refrigerator or off-site in case a transfusion is needed, cannot be returned to stock if not transfused within 30 minutes of removal from controlled storage.
There is general concern among blood services and hospitals that a considerable number of RCC are lost unnecessarily as a result of the 30 minute rule. Data from the UK Blood Stocks Management Scheme (BSMS) repeatedly shows approximately 10,000 RCC are discarded every year due to out of temperature control excursions outside of the laboratory, and this represents almost one quarter of all red cell wastage.³ In a recent survey of hospitals by the BSMS, over 96% of respondents indicated that extending the 30 minute rule to 60 minutes would enable most of their out of temperature control units to be re-issued.
A systematic review published by Brunskill et al in 2011⁴, concluded that
“It is possible that the 30-minute rule could be extended to a “60-minute rule,” but the main concern remains bacterial growth in any contaminated units that are returned to clinical stock… and further studies are required before that question is answered.” The papers reviewed by Brunskill et al are summarised below, along with those subsequently published and recent reports from NHSBT in response to the call for “robust, modern studies using multiple combinations of blood, current anticoagulant and additive solutions, and with defined temperatures and times of exposure that are relevant to current clinical practice.”