41 Validation of Thromboxane A2 Analogue U46619 in Whole Blood Platelet Aggregation to Diagnose Platelet Disorders (2024)

Thromboxane A2 analogue U46619 is conventionally used in platelet-rich plasma aggregometry (optical method) to diagnose platelet disorders. However, a significant proportion of the normal population is nonsensitive to U46619 (~10–20%). Noteworthy, a protocol for the use of U46619 in whole blood aggregometry (impedance method) is yet to be established and published. Herein we aimed to validate the use of U46619 in whole blood aggregometry, and improve its sensitive and specificity to detect secretion problems. Serial doses of U46619 (calculated based on hematocrit adjustment) where tested in whole blood from normal donors. After an optimal concentration was chosen, 45 normal donor samples were tested to establish a reference range. Also, we tested if the addition of the chemiluminescence reagents (luciferase and luciferin) to detect ATP secretion improves the sensitivity and specificity. More than 100 cases were analyzed using U46619 as part of a panel including other common platelet agonists such as ADP, collagen, arachidonic acid, thrombin, and ristocetin. The addition of the chemiluminescence reagents significantly improved the platelet aggregation response in normal donors: in the cohort without chemiluminescence reagents, approximately 10% were nonsensitive (no aggregation detected), whereas in the cohort with chemiluminescence reagents the average aggregation response (as measure in ohms) doubled. Therefore, the specificity is 98%, as determined by the number of cases diagnosed as “normal” or non-clinically significant but showed abnormal platelet aggregation response to U46619. The sensitivity was also high, 92%, as determined by the number cases with abnormal response that were diagnosed with a platelet disorder using further confirmatory testing (platelet electron microscopy or molecular testing). In summary, U46169 in whole blood aggregometry is highly sensitive and specific for detection of platelet disorders, in particular storage pool disorders. Furthermore, U46619 is extremely useful to differentiate aspirin-like defects from secretion problems. Finally, we will present examples of U46619-induced platelet aggregation and ATP secretion in a series of common platelet disorders, including Bernard-Soulier, Glanzmann thrombasthenia, aspirin-like defects, and storage pool disorders, as well as other rare platelet disorders such as Rett syndrome, Paris-Trousseau syndrome, and Noonan syndrome.