To the Editor.
—The study by Dr Nutting and colleagues1 regarding problems in laboratory testing in primary care explores an issue that is becoming increasingly pertinent as managed care grows. Many managed care organizations are now signing exclusive contracts with national laboratories to perform the laboratory testing for their members.However, I was concerned by the authors' inclusion of the misstatement of the therapeutic range for prothrombin time by a referral laboratory as a problem judged to have a significant impact. It is noted that based on this, the patient developed a hematoma, presumably by an inappropriate adjustment in the warfarin dosage by the physician. This study took place during 1993, a time when many, if not most, laboratories were reporting the prothrombin time using either the time in seconds and the prothrombin time ratio, or, if the laboratory was progressive, also reporting the international normalized ratio (INR). Determining a
Hirsch RL. Laboratory Testing in Primary Care. JAMA. 1996;276(3):197. doi:10.1001/jama.1996.03540030031021