Advantages of Sensitive Assays for Thyrotropin in the Diagnosis of Thyroid Disorders

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Abstract
Using two new immunoradiometric assays for thyrotropin, we measured thyrotropin levels in serum of patients suffering from various clinically and biochemically diagnosed thyroid disorders, and in healthy controls. A thyroliberin stimulation test was performed in all patients and controls. Thyrotropin levels were measured using a solid phase IRMA in 339 patients and a coated tube sandwich assay in 152 patients. The lower limits of detection of 0.1 mU/l (solid phase IRMA) and 0.02 mU/l (coated tube sandwich assay) as well as the specificity of these two assays were superior to those of conventional thyrotropin assays. Basal thyrotropin values were clearly different between euthyroid controls and patients non responding to thyroliberin stimulation. However, the values for these two groups overlapped those for patients showing a subnormal increase upon stimulation with thyroliberin. The thyroliberin stimulation test in patients with autonomous adenomas, together with the measurement of thyrotropin using these sensitive assays, provides additional information in the low range below 1.0 mU/l, i.e. below the lower limit of detection of conventional double antibody radioimmunoassays.