A method for the quantitative assessment of platelet-induced clot retraction and clot strength in fresh and stored platelets

Background and Objectives: The changes that occur in platelets as they unde rgo storage have been documented by aggregometry as well as by flow cytomet ry. However, one of the most essential platelet functions, the induction of clot retraction, has not been quantitatively assessed in stored platelets. We describe two potentially useful methods, platelet-induced clot retracti on and clot strength, to assess effect of storage of platelets in blood ban ks or of platelet preparations subjected to freezing or freeze-drying. Thes e methods have previously been developed for bedside monitoring of patients receiving c7E3 (Reopro(R)). Materials and Methods: Platelet-induced clot r etraction (PICR) and clot strength were measured with the Hemodyne(TM) and Thromboelastograph(R), respectively. Paired Study: Fresh platelet concentra tes (n = 3) were obtained from leukapheresis donors and divided into two eq ual units; one unit was tested within 4 h of collection and the other store d for 5 days at 22 degrees C in a platelet incubator and tested. Unpaired S tudy: Fresh platelet concentrates (n = 15) were obtained from leukapheresis donors and tested within 4 h of collection and compared to outdated platel ets (n = 30; random or single donor) that had been stored for 5 days at 22 degrees C in a platelet incubator. Alternative Presevation Methods: Lyophil ized platelets, platelets chilled to 4 degrees C, platelets frozen at -70 d egrees C in 5% dimethyl sulfoxide (DMSO) or in the absence of a cryoprotect ant. Results: Paired Study: Stored platelets demonstrated an increase in PI CR; the difference was not significant (p = 0.55). There was no difference in clot strength between fresh and outdated platelets (p = 0.90). Unpaired Study: When compared to fresh platelets, stored platelets demonstrated a 2- fold higher PICR (p = 0.0011), On the other hand, there was no difference i n the time to onset of PICR (p = 0.08) and there was no difference in clot strength between fresh and outdated platelets (p = 0.14). Alternate Preserv ation Methods: In contrast, PICR and clot strength were reduced in platelet s frozen at -70 degrees C in 5% DMSO and absent in lyophilized platelets, i n platelets frozen at -70 degrees C in the absence of cryoprotectants or st ored at 4 degrees C. Conclusion: The data indicate that the ability of plat elets to induce clot retraction and to enhance clot strength is not altered by storage, despite functional abnormalities in aggregation and agglutinat ion. These data suggest that quantitative measurements of PICR and clot str ength may be simple, useful tools for assessing the function of stored plat elet concentrates, platelets that have undergone freezing or exposure to al ternative buffers and for evaluating platelet functions relevant to PICR.