The importance of sampling site in the measurement of whole-blood platelet flow cytometry

Abstract

Purpose: Flow cytometry is an emerging technology that may be of use in clarifying the defects of platelet function after cardiopulmonary bypass. However, the technique used for platelet sampling may affect results. The objective of this study was to evaluate the influence of the sampling site on the degree of expression of a variety of platelet-associated proteins.Methods: Whole-blood flow cytometric assays for the detection of platelet glycoprotein (GP) lb, guanosine monophosphate (GMP)-140, thrombospondin, activated GPIIb/llla, and platelet-associated factor (FXllla) were developed. These markers were then measured in samples taken simultaneously from a peripheral vein, radial artery, and the side port of the central venous catheter, in eight patients about to undergo surgery.Results: When multiple samples from individual patients were assessed, the degree of activation with all of the activation assays (GMP-140, thrombospondin, activated GPIIb/IIIa, FXIIIa) was significantly greater in samples taken from the arterial catheter (p < 0.05) compared with the central venous catheter or the peripheral vein. The mean difference between sample sites was calculated in the study patients. Percent activation of FXllla from arterial blood was significantly greater than from the central vein and the peripheral vein (arterial-peripheral venous, 18.7 ± 8.6; central venous-peripheral venous, 3.7 ± 3.6; p = 0.005). There was no site-related difference in the detected expression of platelet GPlb.Conclusion: The site of platelet sampling significantly affects the degree of activation detected by flow cytometry. To approximate results that would be obtained from peripheral blood, samples should be taken from the side port of the central venous catheter and not from the arterial catheter in patients studied during surgery.