[A study of antithrombin systems during heparin therapy].

Plasma levels of three thrombin inhibitors (antithrombin III--AT-III-, alpha 2 macroglobulin - alpha 2M -; alpha 1 antitrypsin - alpha 1 AT-) were measured, together with total plasma antithrombin activity (Howie's method), in 19 hospital patients with venous thromboembolic disease before and during heparin therapy. A decrease in AT III levels was observed during treatment and found to correlate significantly with heparin plasma levels, but there were no significant changes in alpha 2M and alpha 1 AT levels. Variations in total plasma antithrombin activity were not significant. In 9 patients whose AT III levels were under 60% a significant increase in alpha 2M level was noted. The therapeutic problems associated with this category of patients are discussed.