MEASUREMENT OF IN-VITRO P-SELECTIN EXPRESSION BY FLOW-CYTOMETRY

Measurement of in vivo platelet activation is difficult after phleboto my and during blood processing for analysis. We used flow cytometry to measure platelet surface expression of P-selectin in the presence and absence of trimethylsphingosine (a platelet activation inhibitor) and compared the results with those from the standard methods of preventi ng in vitro P-selectin expression. Percent activation was calculated a s a ratio of mean sample fluorescence to 100% mean fluorescence after phorbol myristate acetate treatment. Twenty-five micromoles per liter of trimethylsphingosine kept in vitro platelet activation below 5% up to 6 hours after collection and below 10% at 24 hours after collection . Trimethylsphingosine failed to prevent platelet activation caused by centrifugation, storage at 4 degrees C, or stimulation with common ag onists. Addition of trimethylsphingosine to whole blood was valuable i n preventing in vitro platelet activation. This compound promises to b e a useful preservative for diagnostic testing of platelet activation.