Screening for Thyroid Dysfunction: Which Test Is Best?-Reply

In Reply. —Our letter 1 was written to accurately reflect optimal practice guidelines for the clinician as currently recommended by the ATA. The letter was prompted by a need to disseminate information as to the diagnostic impact of recent improvements in TSH assay sensitivity on optimal thyroid test selection. In the opinion of our experts, other recent guidelines 2 not fully utilizing the newer TSH assays do not reflect optimal practice, particularly since the role of TSH measurement in detection of subclinical thyroid dysfunction and in monitoring and adjusting levothyroxine therapy is given inadequate recognition. We would not argue with Helfand and Schmittner that "published studies do not justify conclusions that TSH is the best initial test in all clinical situations." Indeed, our letter clearly takes the position that no test is best in all clinical situations. However, the well-established log/linear relationship between TSH and FT 4 I dictates that