[Evaluation of a new strategy for detecting thyroid dysfunction]

The results of a diagnostic strategy to evaluate thyroid function were assessed. This strategy consists of TSH measurement as the initial biochemical test, assuming that all individuals with normal TSH concentrations are euthyroid and do not require additional measurements of other hormones. The study was carried out in 576 patients whose serum samples had been referred to the laboratory during 4 consecutive weeks for the evaluation of thyroid function. In all cases TSH and free T4 (FT4) concentrations were measured by chemoluminescence, using one tube for each parameter and patient. Total T3 concentrations (T3) were only measured (RIA) in patients with subnormal TSH values, using duplicate samples. With TSH measurement as the initial test, 447 patients (78%) in whom further hormone assessment would not have been required were detected. This rate would have been 75% if FT4 measurement had been adopted as the screening test. In addition, 55 patients with subclinical thyroid dysfunction were identified with TSH measurement. They would have been missed if the screening had been based on FT4 only. T3 measurement only contributed to the identification of one patient with T3 thyrotoxicosis, and it did not provide additional useful information for the diagnostic classification of the remaining patients. The results of these assays show that TSH measurement is the biochemical test of choice as the first step of a strategy to detect thyroid dysfunction. Its use to this end makes the concomitant measurement of other hormonal parameters unnecessary, resulting in a considerable reduction of cost.