[Ultrasensitive TSH : a new diagnostic approach to hyperthyroidism].

The value of new ultrasensitive and rapid immunoradiometric assay of thyroid stimulating hormone (TSH) for the diagnosis of hyperthyroidism was assessed in 130 patients with suspected hyperthyroidism and in 330 controls. The diagnosis was established by the clinical evaluation, thyroid scintigraphy and serum concentrations of thyroid hormones. Using the ROC (Receiver Operating Characteristic) curve methodology which allows the optimization of sensitivity and specificity, the physician can choose the "Cut-off" value between hyperthyroidism and euthyroidism. Two points of the curve seem to be interesting : using the "cut-off" value of 0.1 mUI/l, sensitivity is 0.98 and specificity is 0.98 ; using the "cut-off" value of 0.3 mUI/l, sensitivity is 1.00 and specificity is 0.92. Using the association TSH and FT4 (Free Thyroxin), sensitivity is 0.94 and specificity is 0.99. Sixty four per cent of euthyroid patients with TSH under 0.3 mUI/l have one or several hot nodules and only two have no thyroid disease. A TRH (Thyrotrophin Releasing Hormone) test was carried out in 63 patients with suspected thyrotoxicosis : basal and TRH stimulated TSH levels were under 0.1 mUI/l. This immunoradiometric assay for TSH may simplify the approach to thyroid function testing in patients with suspected thyrotoxicosis : a basal TSH under 0.3 mUI/l is sufficient to confirm a clinical suspicion of thyrotoxicosis without TRH test within four hours. In a department devoted to testing thyroid function, this new method provides a great benefit in cost and work.