Multi-center study of a new technique for measuring free thyroxin in serum.

Abstract In a multi-center trial we evaluated the accuracy of a new assay kit for free thyroxin (T4), the Behring free T4 RIAgnost, in 1036 subjects: 379 normal subjects, 536 patients with thyroid dysfunction, and 121 subjects with no thyroid dysfunction but with conditions that potentially could interfere with the assay. The kit combines immunoextraction and the use of a modified tracer. Although some limitations remained in using a direct assay method for free T4 in certain nonthyroid conditions, this test was superior to one based on the use of a T4 analog. This kit seems to be very accurate for the diagnosis of untreated thyroid pathologies.</jats:p