Endocrine Abstracts

: The management of endogenous subclinical hyperthyroidism is largely guided by perceived risk, including the presence of cardiovascular disease, atrial fibrillation or osteoporosis. We have utilised a fourth-generation TSH assay, providing a 10-fold increase in sensitivity compared to third-generation assays, to determine whether patients with subclinical hyperthyroidism can be differentiated from those with overt hyperthyroidism, based on their now measurable TSH levels. Two groups of patients were identified using thyroid function tests measured with a traditional third-generation assay (Roche). The first (Group 1) had normal free thyroid hormone levels and the second (Group 2) had elevated free thyroid hormone levels. Both had a suppressed TSH (<0.02). The samples were then re-analysed using a fourth-generation assay (Olympus AU3000i) and the values compared. All results are given as median and interquartile range. Group 1 (n=23, M:F 4:19), free T4 17.5 pmol/l (15.8–19.9), free T3 6.1 pmol/l (5.5–6.3); Group 2 (n=54, M:F 14:40) free T4 32.3 pmol/l (25.7–54.9), free T3 pmol/l 10.7 (7.9–13.0). Group 1 fourth-generation TSH 0.009 mU/l (0.007–0.014); Group 2 0.004 mU/l (0.003–0.008) (P<0.001, Mann–Whitney U). Whilst group 1 has a significantly greater fourth-generation TSH than group 2, comparison of the interquartile ranges confirms significant overlap. In group 1 12/23 patients had fourth-generation TSH values above the upper limit of the interquartile range of those with overt hyperthyroidism (group 2). Thus, the measured fourth-generation TSH may be of value in determining the need for treatment. Those in group 1 with TSH values falling within a comparable range to those with overt hyperthyroidism should be considered for treatment, whilst those with greater TSH values could be monitored for progression. Our data suggest that a fourth-generation TSH assay is of value in assessing which patients with subclinical hyperthyroidism should be treated and those who should be monitored.