Background: Previous studies have shown that cooling whole blood to 22 degrees C immediately after collection allows it to be held for up to 16 hours before component preparation (overnight-hold method) without a significant decrease in the quality of components obtained. A study was designated to evaluate the effect of the overnight-hold method on the growth of bacteria in experimentally contaminated blood units.
Study design and methods: Twenty whole-blood units were inoculated with Staphylococcus epidermidis (300 colony-forming units [CFU]/mL; n = 10) or Escherichia coli (50 CFU/mL; n = 10) immediately after collection. Half the units of each group were fractionated 6 hours after collection and the other half after storage for 16 hours at 22 degrees C. Twenty additional whole-blood units were divided in two equal parts, one of which was white cell reduced before inoculation. These 40 half-units were inoculated with S. epidermidis or E. coli and processed by the overnight-hold method. The growth of bacteria was assessed in platelet concentrates on the second and fifth days of storage, in packed red cells on Day 35, and in fresh-frozen plasma after 60 days.
Results: No bacteria growth was detected in plasma or red cell units. On the second day of storage, both bacteria strains grew more slowly in platelet concentrates obtained from blood processed by the overnight-hold method. This difference disappeared for S. epidermidis on the fifth day. When white cell-reduced and non-white cell-reduced whole-blood units were compared, platelet concentrates from the latter showed a delayed growth of both bacterial strains on the second and fifty days of storage.
Conclusion: Prolonged storage of whole-blood units at 22 degrees C before component preparation delays bacteria growth. This effect seems to be mediated by white cells.