The “30-min rule” that states red blood cells must be discarded after being out of refrigeration for 30 minutes can be safely extended to 60 minutes, UK authorities say.
Exposure of red cell units to temperatures of 30 degrees C for up to 60 minutes had no significant impact on the growth of cold-tolerant or mesophile bacteria linked to sepsis, a study by the NHS Blood and Transplant Service found.
The findings, published by the UK’s National Bacteriology Laboratory, would allow blood transfusion services to markedly reduce wastage of red cell units discarded due to being out of controlled temperature storage (CTS), the authors of the study suggest.
Writing in Vox Sanguinis they say the NHS discards more than 10,000 red cell units a year at a cost of more than $2 million, much of which was due to breaches of the 30-min rule.
The rule was based on research from the 1970s which showed that it took about 30 minutes for the surface temperature of red cell units to reach 10 degrees C after being taken out of refrigeration at 2-6 degrees. The 30-min rule was set as a safeguard to minimise the proliferation of bacterial contaminants that may be present in the red cell unit.
However the researchers said subsequent research had suggested this rule was excessively conservative and there was minimal risk of bacterial proliferation, particularly given the very low risk of bacterial contamination of whole blood of 0.29%-0.39%.
Therefore in a laboratory study they assessed the effects of temperature on growth of bacterial species previously implicated in rare cases of red cell transfusion sepsis.
Samples of red cell units were spiked with cold-tolerant species such as Pseudomonas putida, Yersinia enterocolitica and Serratia liquefaciens, and mesophile species Enterobacter cloacae, Bacillus cereus and Staphylococcus epidermidis.
Following exposure of units to 30 degrees for 60 minutes, no evidence was found for significant growth of any of the species after 28 days compared to exposure for 30 minutes. Bacterial counts remained broadly similar to those of units in cold storage, regardless of temperature excursions.
There was some suggestion of deterioration in quality markers of red cell units following repeated 60 minute exposures.
“It is clear from the published Canadian studies and the work presented here that the rule governing out of temperature-controlled storage of red cells can be safely extended to 60 minutes without compromising patient safety,” they concluded.
“Up to 60 min out of controlled temperature is acceptable providing the unit is refrigerated for at least 6 hours prior to reissue to allow it to return to 4°C; such units should not be out of controlled temperature for between 30-60 minutes on more than three occasions,” they added.
However, they also suggested that each blood service conduct its own validation exercise of the 60-min rule to take into account local factors such as manufacturing process, anticoagulants, complement and residual plasma content.