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 catheterization. Patients receiving warfarin therapy occasionally are seen at the catheterization laboratory for emergent procedures. The effects of warfarin on ACT activity have not been previously described. We compared the ACT and the international normalized ratios (INR) in 77 patients receiving warfarin and 57 patients who were not receiving any anticoagulation (controls). Results Both the mean ACT (131 +/- 17.0 seconds) and INR (2.5 +/- 0.90 seconds) of the anticoagulated patients differed 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 warfarin group (r = 0.70, P < .001). There was no relation between ACT and INR in the control group. Conclusion Patients receiving warfarin therapy will have a linear increase in ACT develop similar to patients receiving heparin therapy.