Development of proficiency testing for detection of bacterial contamination of platelet products

Accrediting agencies now require quality control for minimizing platelet (PLT) bacterial contamination (PBC). A proficiency testing (PT) strategy for PBC testing was developed.

During Phase 1, validation of the pH meter and an enhanced bacteria detection system (Pall eBDS)--methods used in our blood bank--was accomplished with two aliquots of an apheresis PLT unit inoculated with Escherichia coli (ATCC 25922, 70 CFU/mL) or Staphylococcus aureus (ATCC 27217, 46 CFU/mL) with an uninoculated aliquot serving as a negative control. Quantitative plate culture was the reference method. PLTs were stored on a rotator at 22 degrees C. Units were sampled in duplicate at 0, 24, and 48 hours. pH testing was considered positive when the pH value was less than 6.6. eBDS was positive when the oxygen concentration was less than 9.4 percent. During Phase 2, synchronized PT of pH and eBDS was performed at four independent sites. PLT samples were inoculated and incubated as above, and aliquots were removed at Time 0 for eBDS testing and at 48 hours for pH testing.

In Phase 1, on inoculated bags eBDS was positive at all time periods but pH was positive only at 48 hours. In Phase 2, synchronized results showed positive eBDS at Time 0 and positive pH at 48 hours on inoculated bags with agreement between paired sites.

This strategy may serve as a useful model for developing PT materials for PBC detection. eBDS was able to identify low levels of PBC, and pH testing, only much higher levels. It is important to carefully coordinate and standardize handling of PT materials and reporting of results.