To the Editor.
—Drs Mennemeyer and Winkelman1 present data relating health outcomes associated with the use of anticoagulation therapy to the type of laboratory where the prothrombin time (PT) test had been performed. I have spent the last 9 months leading a quality improvement task force that has developed guidelines for the use of warfarin in our hospital/physician organization. This project has shown that there are numerous reasons for adverse outcomes caused by the use of warfarin, most of which were not mentioned in this article. It would be unfair to conclude that this article supports further regulation of physician office laboratories as proposed under the Clinical Laboratory Improvement Act of 1988 (CLIA '88) regulations.The article did not mention whether the results were reported as an international normalized ratio (INR) or as a PT-control ratio. Failure to use the INR system could account for the increase in adverse