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

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Abstract

BACKGROUND

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

STUDY DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

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