We sample each platelet component at 24 hours after collection.
Samples are then screened on the bioMerieux BacT/ALERT Automated Microbial Detection System, which uses both aerobic and anaerobic culture bottles.
After sampling, we issue platelets as ‘negative to date’ but we continue to incubate cultures over the full shelf life of the components.
We incubate beyond the expiry by 3 days (eg, 7 day incubation after 24 hours/5 days expiry of platelets).
If a culture becomes positive, the screening equipment automatically flags this as ‘initial machine positive’ (IMP).
An IMP is not conclusive evidence that the component is contaminated and many eventually turn out as false positives.
As a sample could potentially flag as a positive at any time during the day, we have set up remote monitoring of the testing system 24 hours a day, 7 days a week (24/7). We also have 24/7 recall with a National Recall Office.
If the platelets and/or their associated components (eg, red cell or plasma) have already been issued at the time of the IMP, our National Recall Office notifies the relevant transfusion laboratory so that recall of the platelet unit and any associated component can be arranged.
If the component has been transfused, the transfusion laboratory shall contact the treating clinician for them to manage the patient with the knowledge of the preliminary result.
We send all IMPs to an external laboratory to have a Gram stain and culture performed. All organisms seen at microscopy in the Gram stain are notified to the relevant transfusion laboratory.
Gram stain results are generally available several hours after the IMP is obtained. Negative Gram stain results are not notified as they are a poor predictor of the absence of contamination and are unlikely to change the management of the patient.
As relevant additional information becomes available, we forward a progress report to the transfusion laboratory, such as donor information that might assist in the therapeutic management of the patient or further information from the culture including bacterial identification.
In all cases where components have been transfused, a final report is forwarded to the transfusion laboratory when all laboratory investigations are complete. Every attempt is made to provide the identification of cultured bacteria. Antibiotic sensitivity testing is also performed, where possible.