PLASMA TISSUE FACTOR ANTIGEN LEVELS IN CAPILLARY WHOLE-BLOOD AND VENOUS-BLOOD - EFFECT OF TISSUE FACTOR ON PROTHROMBIN TIME

To measure the amount of tissue factor released during specimen collec tion and its potential effect of shortening the prothrombin time, we m easured tissue factor and prothrombin time in twenty-three paired veno us and capillary blood samples from anticoagulated patients and in ten paired samples from controls. We also compared venous prothrombin tim e determined by a plasma-based assay with venous and capillary prothro mbin time determined with a whole blood assay. Venous specimens were o btained using a two-syringe technique; capillary specimens were obtain ed by fingerstick after wiping the first drop of blood. Plasma tissue factor was determined by an enzyme-linked immunoabsorbant assay. The p atients' mean venous tissue factor (235 +/- 101 pg/ml) and capillary t issue factor (268 +/- 106 pg/ml) were higher than those of the control s (161 +/- 42 pg/ml and 187 +/- 63 pg/ml, respectively, P < 0.05). The se differences disappeared after adjusting for age. Capillary tissue f actor levels were higher than venous tissue factor (244 +/- 102 pg/ml vs. 213 +/- 93 pg/ml), with a mean difference of 31 pg/ml (P = 0.0001) . In addition, whole blood prothrombin time was lower in the capillary than in the venous samples (17.7 +/- 5 sec vs. 18.3 +/- 5.4 sec, P = 0.004). However, there was no correlation between capillary-venous dif ferences in tissue factor and capillary-venous differences in the whol e blood prothrombin time. Whole blood capillary and venous prothrombin times highly correlated with the plasma-based venous prothrombin time (r = 0.98, P < 0.0001). These results demonstrate that obtaining bloo d by fingerstick does not result in a clinically significant release o f tissue factor. In addition, we did not observe any interference of p lasma tissue factor with the whole blood prothrombin time assay. A dir ect relationship between tissue factor and age was observed. (C) 1997 Wiley-Liss, Inc.