Response to Letter by Albright et al
I thank Dr Albright and her colleagues for identifying an incongruity in determination of the level of anticoagulation among persons taking warfarin between the American Heart Association/American Stroke Association guidelines and the trial that originally tested the use of intravenous administration of recombinant tissue plasminogen activator in the treatment of acute ischemic stroke. The difference reflects the conversion in the methodology to assess the level of anticoagulation from the past use of the prothrombin time to the current use of the international normalized ratio. For the discrepancies in the levels of prothrombin time among laboratories that Dr Albright and her colleagues clearly describe in their letter, the guidelines panel decided to use the international normalized ratio of <1.7 as the measure of the degree of anticoagulation rather than the prothrombin time value originally used in the trial. There are circumstances such as their case in which the international normalized ratio of 1.7 does not correspond to a prothrombin time of 15 seconds, a level that may be recorded as normal in some laboratories. However, the widespread use of the international normalized ratio instead of prothrombin time seems to have been successful in that the rates of bleeding complications after intravenous thrombolysis in the community setting appear to have not exceeded those reported in the original trial. Therefore, it seems reasonable to use only the results of the international normalized ratio test to determine eligibility for thrombolytic therapy.