Reproducibility of two in vivo tests of platelet function

We correlated repeat determinations of platelet aggregate ratios (PAR) and plasma beta-thromboglobulin (BTG) in the right and left arms of thirty-four subjects in order to measure test reproducibility and to evaluate the effects of venipuncture. The reproducibility of PAR on the same blood samples was relatively low but similar to that obtained when the right arm and left arm values were compared, thus indicating little variation secondary to venipuncture. For BTG, the reproducibility on identical blood samples was quite high, but fell significantly when plasma samples from the two sides were correlated. This finding and increased BTG values when obvious blood collection problems occurred, indicated that plasma BTG levels are quite sensitive to venipuncture technique.