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—Dr Hirsch raises an important point with our study and appropriately questions whether the specific instance described was an error on the part of the referral laboratory in reporting the result of the prothrombin time or whether the error resulted from incorrect interpretation of that result on the part of the primary care physician. In this case, the referral laboratory reported the prothrombin time as the INR, but according to the reporting physician "falsely calculated the INR desirable range up to 6.96 for type 'A' indication for warfarin." The reporting physician further explained that this problem persisted for 2 months and affected at least 1 patient who developed a hematoma as a result of upward adjustments in the warfarin dosage.Consequently, we believe this event was correctly characterized as a problem in laboratory testing, rather than an error of interpretation.
Nutting PA, Pontious M, Colo D, Stull TM, Boone JD. Laboratory Testing in Primary Care-Reply. JAMA. 1996;276(3):197. doi:10.1001/jama.1996.03540030031022