HOW DOES WARFARIN AFFECT THE ACTIVATED COAGULATION TIME

Background The activated coagulation rime (ACT) is a rapid measurement of a patient's level of heparin anticoagulation during cardiac cathet erization. Patients receiving warfarin therapy occasionally are seen a t the catheterization laboratory for emergent procedures. The effects of warfarin on ACT activity have not been previously described. We com pared the ACT and the international normalized ratios (INR) in 77 pati ents receiving warfarin and 57 patients who were not receiving any ant icoagulation (controls). Results Both the mean ACT (131 +/- 17.0 secon ds) and INR (2.5 +/- 0.90 seconds) of the anticoagulated patients diff ered from the controls (ACT = 115 +/- 14.5 seconds, INR = 1.0 +/- 0.10 seconds; P < 0.05). The ACT increased linearly with INR in the warfar in group (r = 0.70, P < .001). There was no relation between ACT and I NR in the control group. Conclusion Patients receiving warfarin therap y will have a linear increase in ACT develop similar to patients recei ving heparin therapy.