Background: Eleven laboratories participated in a study investigating whether swirling can be used in monitoring platelet discoid morphology in platelet concentrates (PCs). Study Design and Methods: In each laboratory, two readers observed the swirling pattern in 1- or 5-day-old PCs, in PCs containing spherical platelets obtained by 4 degrees C storage (spherical PCs), and in PCs containing known proportions of spherical and discoid platelets. Swirling was reported as positive, intermediate, or negative. Moreover, platelet morphology was evaluated by oil-phase microscopy. Results: Swirling of spherical PCs was found to be positive and negative in 5 and 68 percent of cases, respectively. Conversely, swirling of fresh PCs was positive and negative in 83 and 2 percent of cases, respectively. Results in PCs containing known amounts of added spherical platelets were intermediate between those in fresh and spherical PCs. The observed agreement between the two readers (number of concordant readings/total readings) was 67 percent. Most disagreements concerned positive versus Intermediate or intermediate versus negative evaluations, whereas a positive versus negative disagreement was observed in only 1 percent of cases. The percentages of discs found by microscopy showed greater variation among the different laboratories, indicating that this measurement should be better standardized. Conclusion: Evaluation of swirling seems promising for large-scale quality control of PCs. Further studies are needed to confirm this hypothesis.
