Effect of tourniquet pressure and intra-individual variability on plasma fibrinogen, platelet P-selectin and monocyte tissue factor.

Small differences in levels of certain haemostatic components may be clinically significant. It is important therefore to eliminate potential sources of confounding variability. This study investigated the effect of removing tourniquet pressure prior to sample collection on plasma fibrinogen levels, platelet P-selectin and monocyte tissue factor expression. Blood was collected from the right arm under maintained tourniquet pressure and from the left arm following the release of pressure once the vein was sufficiently inflated for insertion of a needle. Whole blood was labelled within one hour of venepuncture to allow analysis of platelet P-selectin and monocyte tissue factor by flow cytometry. Plasma fibrinogen levels were analysed in samples stored at -70 degrees C, for all individuals at the end of the study using a method based on the Clauss technique. Intra-individual variability for each of the components was assessed by collecting samples under tourniquet pressure from four individuals on the same day on three consecutive weeks. Intra-individual variations were greater than assay CVs for all three components. There were no significant differences between the two tourniquet methods of collection for fibrinogen, P-selectin or tissue factor. In conclusion, there is no reason not to use a tourniquet during collection of blood for analysis of plasma fibrinogen, platelet P-selectin or monocyte tissue factor.