Platelet Sample Characterization
Platelet concentrates are primarily comprised of plasma (the medium), platelets, and microparticles (small pieces of platelets that have fractured from the cells over time). Historically, platelet concentrates were evaluated by the platelet content to make sure that the dose was high enough, or in other words, that there were enough platelets in a given volume. Samples would be taken from the platelet concentrate and analyzed using automated cell counters to determine the platelet count. However, the platelet count method does not address sample heterogeneity, the viability or the functionality of the platelets. The presence of microparticles is an indicator of platelet viability. Microparticles are fragments shed from platelets in response to various types of stress and stimulation. Thus, lower microparticle content in a sample suggests that the platelets have not previously been stressed, are intact and have not broken down.
In addition, platelets respond to temperature variation, and when cooled they “activate” to extend pseudopods, radial tentacles emanating from the cell, and form microaggregates. Functional platelets will activate readily when heated or cooled, whereas non-functional platelets will not respond to temperature stress.
The overall characterization of the platelet sample can therefore be determined by considering the platelet count, the temperature response of the platelets, and the ratio of microparticles to platelets.