The one-step approach to thyroid function tests. The diagnostic thyroxine ratio (DTR)/serum thyroxine (T4) level combination.

A one-step approach to thyroid function tests is reported, using Tetralute kits (Ames). Two parameters are obtained simultaneously--namely, the serum thyroxine (T4) level and the diagnostic thyroxine ratio (DTR), which correlates well with the free thyroxine index (FTI) as determined by two separate tests-the T4 level and the triiodothyronine resin uptake ((T3U)) estimations. Data presented from patients with a variety of thyroid states prove that the DTR, particularly in combination with the T4 level, is adequate for the assessment of thyroid dysfunction in almost all circumstances.