title: Platelet involvement in the activated coagulation time of heparinized blood.
abstract: The activated coagulation time (ACT), commonly used during cardiopulmonary bypass (CPB), is assumed to measure only differences in heparin levels. Studies were undertaken to determine whether platelet activation/inhibition might also influence the test. When either the platelet inhibitor prostacyclin or the platelet activator adenosine diphosphate (ADP) was added to healthy donor blood containing 2 IU of heparin per ml, there was significant prolongation of the ACT (prostacyclin: mean prolongation, 60.6%; ADP: mean prolongation, 52.3%). In blood taken from the extracorporeal circuit of ten CPB cases, the prolongation with the platelet inhibitor carbacyclin, a prostacyclin analogue, was infinite. It is concluded that the ACT as used during CPB must be interpreted as a measure of both platelet procoagulant activity and heparin activity. Furthermore, this dual sensitivity, while fortuitous, is probably advantageous; patients with hyporeactive platelets will automatically receive less heparin.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D001777:Blood Coagulation / Q000187:drug effects*; D002315:Cardiopulmonary Bypass; D011464:Epoprostenol / Q000494:pharmacology / Q000031:analogs & derivatives; D006493:Heparin / Q000097:blood / Q000494:pharmacology*; D006801:Humans; D010314:Partial Thromboplastin Time; D010974:Platelet Aggregation / Q000187:drug effects*; D010976:Platelet Count; D014914:Whole Blood Coagulation Time
chemical_list: D000244:Adenosine Diphosphate; C026678:carboprostacyclin; D006493:Heparin; D011464:Epoprostenol