Platelet function is critically important in the acute-care settings of cardiopulmonary bypass surgery and percutaneous coronary intervention, which are commonly associated with the adverse vascular events of hemorrhage and thrombosis, respectively. To improve outcomes, it has been suggested that patients should be screened for platelet count and function periprocedurally, and therapeutic intervention including the possible use of thrombolytics and adequate anticoagulation or administration of antiplatelet agents, should be utilized. Antiplatelet therapy including aspirin (acetylsalicylic acid), the thienopyridines (clopidopgrel), and parenteral anti-glycoprotein (GP) IIb/IIIa agents (abciximab, tirofiban, and eptifibatide) are recognized as clinically important in patients at risk of developing thrombotic events. Recently, it has been recognized that empiric therapeutic administration of these agents may be suboptimal in clinical environments because of interpatient variability with regard to platelet count, platelet response, receptor concentration on the platelet, and other factors. Hence there is a clinical need to monitor such therapies on an individual basis. Traditional platelet tests including light transmission aggregometry (LTA) are inconvenient for acute diagnostic testing because of the complexity of the test and the requirement for specialty training. Hence, 'near-patient' test systems have recently been introduced. Plateletworks is an in vitro diagnostic, point-of-care test platform that has demonstrated utility in monitoring platelet response to all current antiplatelet agents including aspirin and clopidogrel.

SummaryAn improved method for the isolation of highly purified active human Hageman factor has been described. An overall recovery of 25% with a purification of 106 has been achieved. Certain of the physical and chemical characteristics of XII have been elucidated. Selective chemical modification of functional groups and a variety of enzymatic assays have been employed in an effort to shed light on the mechanism of action of this procoagulant.

SummaryVarious materials and conditions have been investigated for their effect on Hageman factor activation. Fatty acid soaps, purified phospholipids, ellagic acid, platelets, and freezing and thawing were among those studied.Under certain circumstances XIIa activity disappeared spontaneously; the factors affecting the kinetics of this “decay” have been evaluated. Successful regeneration of this “decayed” XII a has been achieved. On the basis of these observations, it is postulated that during its “decay”, XIIa reverts to XII by spontaneous molecular refolding.

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Two laboratory procedures: the heparin thrombin clotting time (HTCT) of O’Brien et al and the platelet catalytic activity (PCA) of King and Joffe are being investigated for their usefulness in prediction and/or diagnosis of a thrombotic or hypercoagulable state in patients with a variety of diseases. Included are patients with current thrombosis, patients with a past history of thrombotic disease, as well as those with a negative history. The HTCT has been reported to correlate with release of platelet factor 4 from platelets destroyed in thrombotic episodes. The PCA was designed and used by King and Joffe to predict successfully postoperative venous thrombosis. In this study, both the PCA and HTCT showed a useful correlation with other laboratory and clinical findings in patients with previous and current thrombosis. In addition, clinical situations in which these tests appear to give misleading results will be presented and analyzed. While this study represents relatively small numbers of patients, the degree of correlation seems to indicate that both the HTCT and PCA have value in assessment of hypercoagulability and thrombosis.