Testing platelet components for bacterial contamination

Bacteria in transfused platelets can cause serious morbidity and, rarely, death. Most contaminating bacteria enter the blood at the time of venepuncture. While many of these contaminants fail to grow in the platelet unit, storage of platelets at 20–24 °C facilitates growth of some organisms, and the cumulative risk of severe sepsis increases with the storage age of platelet components. Several methods have been developed or adapted to attempt to detect contaminating bacteria with high sensitivity and specificity, but the perfect test has yet to be found. Testing early in the platelet component’s shelf life, even using exquisitely sensitive culture-based tests, is compromised by major problems of sample error – there may be too few bacteria present at this stage to ensure that any practical sample volume contains even one of them. Culture techniques are too slow to be useful as a release test. On the other hand, available rapid tests are too insensitive to use early in the shelf life, and have yet to show convincingly that they are sensitive enough for testing close to the time of transfusion. Nevertheless testing for bacteria in platelet components represents a significant advance in blood transfusion safety, and prevents the transfusion of many hundreds of bacterially-contaminated platelet units each year.