In vivo platelet retention in human bleeding-time wounds. I. Normal subjects and patients with platelet dysfunction

PRB was measured in standardized skin puncture wounds. Platelets in wound blood samples collected in EDTA-heparin-containing micropipettes were counted electronically following gravity separation of plasma. The relationship between the wound platelet count (expressed as percent of the venous blood platelet count) and time was found to be linear during the first 3 min of bleeding. The slope of the linear regression line for percent of venous blood platelet count vs. time was 20.8 ± 8.9 (mean ± S.D.) in 31 normal subjects. Nine of 10 patients with significant, nonpharmacologic platelet dysfunction were found to have markedly decreased PRB. The determination of PRB was found to be reproducible, and control studies excluded platelet clumping and sedimentation of platelets as factors which significantly influenced the results. In contrast to previous observations, the results of this study indicate that platelets are removed from circulating blood at an increasing rate during the first 3 min of bleeding in normal subjects. Furthermore, a significant degree of EDTA-reversible clumping of platelets normally occurs during bleeding. The method described permits an accurate assessment of the quantitative and dynamic aspects of platelet participation in the arrest of bleeding. The determination of PRB holds promise in the evaluation of the biological significance of in vitro evidence of platelet dysfunction, and it may be useful in the evaluation of patients with hemorrhagic and thromboembolic disorders.