To clarify the effect of blood sampling through the indwelling catheter on indices of platelet function, we measured the levels of plasma β-thromboglobulin (βTG) and platelet factor 4 (PF4). In 12 patients with heart disease, direct sample was obtained by two-syringe technique with a 21-gauge needle inserted into the antecubital vein and catheter sample was also obtained immediately after advancing a 16-gauge Teflon catheter of 50cm length into the superior vena cava. In 4 patients (33%), catheter sample showed extremely high levels (more than 50%) of both βTG and PF4 as compared with those of direct sample. In 7 normal subjects, direct samples were obtained from the right and left antecubital veins immediately before and 45 minutes after catheterization, respectively. Catheter sample was also obtained 45 minutes after catheterization., βTG and PF4 levels of direct sample obtained 45 minutes after catheterization (21±6 and 5±1ng/ml, respectively) were similar to those before catheterization (22±8 and 5±1ng/ml), while their levels of catheter sample (66±36 and 18±10ng/ml) were significantly higher than those of direct samples. In another 4 normal subjects, catheter samples were repetitively withdrawn through a Teflon needle of 6cm length immediately after insertion to the antecubital vein and 10, 15 and 30 minutes thereafter. βTG and PF4 levels increased progressively (βTG: from 19±7 to 106±49, PF4: from 6±1 to 44±28ng/ml). Microscopy of the inner surface of the indwelling catheter disclosed massive platelet aggregates and fibrin strands. This study demonstrated that collection of blood through the catheter of any length caused an artificial elevation of plasma βTG and PF4 levels, which was derived from catheter-induced platelet α-granule release, and that catheter insertion itself had no effect of artificial increase in βTG and PF4 in vivo.
