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August 1992

Anticoagulation and Prothrombin Time Ratios

Author Affiliations

Tulsa, Okla

Arch Intern Med. 1992;152(8):1720. doi:10.1001/archinte.1992.00400200144026

To the Editor.—  The article by Bussey et al1 and the accompanying editorial by Hirsh2 on prothrombin time (PT) ratios and errors in anticoagulation therapy in the February 1992 issue of the ARCHIVES were both informative and extremely important in the area of anticoagulation. Unfortunately, these articles did not address what seemingly is a fundamental question in this area. It seems as though, instead of relying on the international sensitivity index the international normalized ratio data, we could simply use the PT control on our patients and compare this to the PT values once our patients undergo anticoagulation therapy, given the fact that for both the control and our patient samples the same thromboplastin is used, regardless of what the international sensitivity index values of the thromboplastin are at that current time. For example, if the PT control is 11.8 seconds and the PT of our patient sample

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