Assessment of a time-resolved fluoroimmunoassay for thyrotropin in routine clinical practice.

We assessed the use of a dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA) system to measure thyrotropin (thyroid-stimulating hormone, TSH) in routine clinical practice. The assay is simple and precise, with intrabatch CV of less than 10% down to 0.1 milli-int. unit/L. When compared with free thyroxin, total thyroxin, and triiodothyronine measurements in 142 patients, the present assay most sensitively indicated hyperthyroidism and, in conjunction with free thyroxin, most sensitively indicated hypothyroidism. Free thyroxin was the most specific assay (lowest number of falsely increased or decreased results) in detecting thyroid disorders, with a specificity of 93.6% as compared with 85.1% for TSH, 81.9% for thyroxin, and 77.6% for triiodothyronine.