These data indicate that HPA-15 alloimmunization needs only to be considered in subjects with suspected FNAITP if no other platelet-specific antibody is detectable. The presence of panreactive or autoreactive antibodies should also be considered in neonatal thrombocytopenia.

Flow cytometric evaluation of platelet function extends our understanding of platelets' role in various clinical conditions associated with either bleeding disorders, thrombosis, or monitoring of antiplatelet therapy. The use of suboptimal concentrations of various agonists may allow assessing the "activatability" of platelets. We determined platelet responsiveness to thrombin-receptor-activating peptide-6, arachidonic acid, adenosine 5c-diphosphate (ADP), epinephrine, collagen, and ristocetin at suboptimal concentrations by determination of P-selectin expression and binding of PAC-1 in 26 healthy male individuals. The response varied considerably from one individual to the next. However, within individuals, responses to all agonists except collagen correlated strongly (p<0.05), suggesting a global variability of platelet responses. Moreover, P-selectin expression and PAC-1 binding were strongly correlated (p<0.05). Interestingly, with epinephrine, PAC-1 positive events outnumbered P-selectin positive events, while this was not seen with the other agonists. Thus, epinephrine may specifically affect the conformational switch mechanism and receptor clustering. Our data indicate that the in vitro response to suboptimal concentrations of agonists varies, but individuals with selective platelet defects may still be identified based on data obtained with the various agonists.

BACKGROUND: Platelet (PLT) collection and storage affect the functional capacity of PLTs in PLT concentrates (PCs). Therefore, PLTs' functional quality should be studied before transfusion. STUDY DESIGN AND METHODS: PCs (n = 15) were collected by a standard apheresis procedure (Trima, Gambro BCT) and were stored for 7 days. Samples were taken to assess PLT adhesion and aggregate formation by a cone and plate analyzer (Impact-R, DiaMed) on Days 1, 3, 5, and 7 after harvesting. This device allows testing PLT function under high-shear stress close to physiologic conditions. Concomitantly, P-selectin expression and the residual responsiveness to TRAP-6 were determined by flow cytometry. RESULTS: PLT adhesion, as measured by surface coverage, decreased during the entire observation period; likewise, the size of aggregates was significantly lower on Days 5 and 7 compared to Day 1 (p < 0.02). P-selectin expression increased from Day 5 to Day 7 (p < 0.04), whereas TRAP-6-inducible expression remained stable until Day 5 of storage and decreased significantly on Day 7 (p = 0.04). CONCLUSIONS: Our results show that high-shearinduced PLT adhesion and aggregation on the polystyrene surface deteriorate upon storage, suggesting decreased PLT function in vivo. Thus, the Impact-R may be a useful tool to assess the functional capacity of PLTs under various PLT harvesting and storage procedures. P latelet (PLT) transfusions are used to prevent or treat bleeding episodes in patients with thrombocytopenia, for example, after high-dose chemotherapy. The process of PLT collection and storage may affect the functional capacity of PLTs in PLT concentrates (PCs). Therefore, a variety of in vitro methods have been extensively investigated for their validity and feasibility to test and guarantee the function of PLTs that were prepared for their transfusion.1 Results from in vitro tests were correlated with the corrected count increment (CCI) of PLTs 1 or 24 hours after transfusion to estimate the validity of these tests clinically. 2-4Although the CCI is most often used to estimate the success of PLT transfusions, it does not always correlate with PLT survival.1 Very few in vitro tests performed on PLTs from PCs, however, correlate with PLT viability after their transfusion to healthy individuals, 4,5 and these tests have not been further validated after transfusion to thrombocytopenic patients. Further, the CCI does not evaluate PLTs' hemostatic activity. Thus, in vitro evaluation of PLT function in PCs is desirable before transfusion. According to the European guidelines, only the pH must be measured (6.4-7.4) and the swirling phenomenon must be demonstrated after 5 days of storage. This device allows evaluation of PLT function under close to physiologic conditions in a whole-blood assay. PLT adhesion and aggregation can be determined in anticoagulated blood under arterial flow conditions wherein a cone and plate viscometer induces laminar flow with a uniform shear stress over a plastic plate by the rotating cone. Results can then be e...

Agonist-inducible activation of platelets in cAITP is affected mainly by their in vivo activation.

Transfused PLTs were detectable by flow cytometry, and their functional activity was demonstrated by the Impact.