Bacterial screening of outdated buffy coat platelet pools using a culture system and a rapid immunoassay

BACKGROUND: Canadian Blood Services performs bacterial screening of buffy coat platelet pools (BCPs) using aerobic BacT/ALERT cultures. This study aimed to determine the rate of detection failures during initial platelet (PLT) screening and evaluate the introduction of anaerobic cultures and immunoassay testing to assess the safety of extending PLT storage beyond 5 days. STUDY DESIGN AND METHODS: Outdated (7- to 10-day-old) BCPs that tested negative during initial screening were assayed with BacT/ALERT and the Verax PLT Pan Genera detection (PGD) test, an immunoassay that detects Gram-positive (GP) and Gram-negative (GN) bacteria. BacT/ALERT aerobic and anaerobic culture bottles were inoculated with 8 to 10 mL of BCP and incubated for up to 6 days. The PGD test was performed following manufacturer's instructions. Positive results were confirmed using the BacT/ALERT and PGD tests, blood agar culture, and Gram staining. Invalid PGD results were investigated. RESULTS: A total of 4002 BCPs were tested with one (0.025%) true positive (Staphylococcus epidermidis) found by both the BacT/ALERT and the PGD assays. Fifty-four (1.35%) false-positive BacT/ALERT cultures were obtained mainly due to instrument errors involving anaerobic cultures. Eleven (0.27%) false-positive PGD tests were observed in the GP window of the strip. Forty-nine (1.2%) invalid PGD results were obtained mostly before implementation of a humidity chamber. CONCLUSION: Testing of outdated BCPs suggests that introducing anaerobic cultures would result in significant PLT wastage due to a high rate of false positives. Contaminated BCPs still escape detection during initial testing; therefore, extension of PLT storage may be possible if repeat screening is performed before transfusion.