Bacterial growth in red blood cell units exposed to uncontrolled temperatures: challenging the 30‐minute rule

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Abstract
Background and Objectives: The ‘30‐min rule’ requires discarding red blood cells (RBCs) exposed to uncontrolled temperatures for >30 min to ensure safe RBC transfusion. This study was aimed at determining whether multiple room temperature (RT) exposures promote bacterial growth.Materials and Methods: Pooled and split RBC units were inoculated with ~1 CFU/ml of Serratia marcescens, Yersinia enterocolitica, Escherichia coli or Staphylococcus epidermidis. Control units remained in storage, while test units were exposed to RT for six 30‐min or three 60‐min intervals. Bacterial concentrations and endotoxin levels were determined after each exposure and at 42 days of storage. RBC core temperature and RT were monitored in mock units with Escort iLog temperature loggers. A mixed model was used for statistical analyses.Results: Red blood cell core temperature reached 10·7 ± 0·4°C and 14·2 ± 0·2°C during 30‐ and 60‐min exposures, respectively. Staphylococcus epidermidis and E. coli did not grow in either control or exposed RBCs. Yersinia enterocolitica concentration and endotoxin levels were similar in both control and test units. Serratia marcescens concentration and endotoxin levels were higher in exposed units; however, differences between units exposed for 30 min or 60 min were not observed.Conclusion: There is no added risk to RBC safety by increasing RT exposures to 60 min with each removal from storage for up to a total of 3 h during RBC shelf life. Therefore, extending the 30‐min limitation in RBCs exposed to uncontrolled temperatures to 60 min should be considered by regulatory agencies.

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