Functional and antigenic antithrombin III in angina pectoris and acute myocardial infarction patients

Plasma antithrombin III was measured by an immunological approach (AT III:Ag) using an antiserum developed in our laboratory and by its ability to inhibit thrombin (functional assay) using a chromogenic synthetic substrate in 12 patients with myocardial infarction, 9 patients with angina pectoris and 10 healthy control subjects. In the early stage (3 to 24 hours after the onset of pain) of an acute myocardial infarction AT III:Ag (115.67% +/- 21.23) was found to be significantly (p less than 0.01) higher than functional (free) AT III (92% +/- 10.27). This difference was less obvious 10 days later (AT III:Ag 118% +/- 18.93; functional AT III 104.94 +/- 14.45). There was also no significant difference between AT III:Ag and functional AT III in patients with angina pectoris as well as in controls. Since AT III:Ag represents total plasma AT III while functional AT III represents only free AT III the difference between these two variables could provide informations about the amount of the anticoagulant forming complexes with activated clotting factors. It is therefore considered that the significant increase in the difference between AT III:Ag and functional AT III in the early stage of acute myocardial infarction is likely to suggest an intravascular activation of coagulation.