Optimal Use of Blood Tests for Assessment of Thyroid Function

To the Editor. —The American Thyroid Association (ATA) in 1990 and 1991 issued guidelines for use of laboratory tests in thyroid disorders. 1,2 These ATA position papers update previous recommendations because of the development and availability of improved thyrotropin (thyroid-stimulating hormone [TSH]) methods capable of clearly separating normal from subnormal serum TSH levels. The highly sensitive TSH assay constitutes a practical, useful, and significant laboratory advance in clinical thyroidology. There is agreement among thyroid specialists that measurement of serum TSH level, complemented by an appropriate free thyroxine (FT 4 ) estimate, represents the best and most efficient combination of blood tests for diagnosis and follow-up of most patients with thyroid disorders. Currently in the investigation of thyroid disease there is a trend to replace a combination of tests (eg, total T 4 + triiodothyronine resin uptake + FT 4 + total T 3 + TSH) by a discriminating single thyroid function test. This trend reflects