A COMPARISON OF THE EFFECTS OF ASPIRIN ON BLEEDING-TIME MEASURED USING THE SIMPLATE(TM) METHOD AND CLOSURE TIME MEASURED USING THE PFA-100(TM), IN HEALTHY-VOLUNTEERS

Aims The aim of this study was to compare the effects of aspirin on pl atelet function as measured by the 'classical' template bleeding time with a new ex viva method measuring closure times using the PFA-100(TM ) machine. Platelet aggregation in response to arachidonic acid was al so measured ex vivo. Methods The trial was a randomized, double-blind, placebo-controlled crossover design, with each volunteer taking 750 m g aspirin (BP) or placebo, three times a day for 5 days, with an 18 da y wash-out period between treatments. Bleeding times and closure times were measured before the first dose on the first day and 0.5 h after the last dose on the fifth day of each treatment period. They were als o measured 2 weeks after the last day of the trial. Results Baseline b leeding times (pre-placebo) were 415 s using the Simplate, whilst base line closure times were 115 s using the PFA-100(TM). Aspirin treatment caused an increase of both the template bleeding time (61%) and the c losure time of the PFA-100(TM) (79%) when compared with the effects of placebo. The platelet aggregatory response to arachidonic acid was co mpletely inhibited following aspirin treatment and was unaffected foll owing placebo. Two weeks after the end of the trial, all values had re turned to pre-treatment levels. The template bleeding time was unalter ed in 1 of the 12 volunteers during aspirin treatment and was signific antly prolonged in 3 of the 12 volunteers during placebo treatment. Th e PFA-100(TM) closure time was unaltered in 1 of the 12 volunteers dur ing aspirin treatment and was prolonged in 1 subject during placebo tr eatment. Conclusions The change in closure time using the PFA-100(TM) is as sensitive and reproducible to the effects of aspirin on platelet function as is the template bleeding time test. However, the PFA-100( TM) produced less variable effects with fewer false positive results.