Pre-analytical and analytical issues in the analysis of blood microparticles

Results of plasma microparticles (MPs) measurements reported in the literature vary widely. This is clearly not only related to the lack of well-standardised MP assays, but also to variations in pre-analytical conditions. In this review we will discuss the pre-analytical variables related to plasma and MP preparation which may affect MP analysis. Additionally we will address several analytical issues in commonly used MP assays and briefly discuss some novel approaches for the detection and characterisation of MPs. Ideally MP measurements should be performed in plasma, freshly prepared directly after blood withdrawal. As platelet contamination seems to be one of the major pre-analytical problems in processing plasma for MP measurement, the use of platelet-free plasma may be preferred. When frozen-thawed plasma is used, especially PMP and annexinV-positive MP counts should be interpreted with caution. When flow cytometry is chosen as a method for quantification of MPs, some analytical conditions should be standardised, e.g. settings of the flow cytometer, quality of the antibodies, and use of counting beads. Fluorescence-nanoparticle tracking analysis and atomic force microscopy can accurately count nanosized MPs, but unfortunately the operational procedures of both methods are still time consuming and they give no information on the functional properties of MPs. The MP-TF activity assay provides information on MPs carrying active TF, regardless of their parental origin. Ultimately, standardisation of pre-analytical procedures and the introduction of reliable and rapid methods for the measurement of MPs are urgently needed to facilitate their use as biomarker in the pathophysiology of diseases.