SFEBES2025 Oral Communications Thyroid (6 abstracts)
Evaluating the difference between thyroid function test (TFT) results (thyroid stimulating hormone (TSH) and free thyroxine (FT4)) in managed hypothyroidism vs screened untreated/euthyroid individuals: analysis of a whole city population database
Adrian Heald 1 , Lakdasa Premawardhana 2 , Peter Taylor 2 , Suhani Bahl 2 , Nadia Chaudhury 3 , Onyebuchi Okosieme 2 , Anthony Fryer 4 , Colin Dayan 2 & Mike Stedman 5
1Salford Royal Hospital, Salford, United Kingdom. 2University of Cardiff, Cardiff, United Kingdom. 3University Hospitals Coventry & Warwickshire, Coventry, United Kingdom. 4Keele University, Keele, United Kingdom. 5RES Consortium, Andover, United Kingdom
Introduction: Over 10 million TFTS are carried out in England annually, most requests coming from primary care. This study aimed to investigate differences in laboratory thyroid-hormone-status in managed hypothyroidism vs untreated/euthyroid individuals taking into accounting diagnostic code/levothyroxine amount prescribed.
Methods: Using a city-wide population record, we analysed TSH/FT4 simultaneous results from 47,869 consecutive diagnosed hypothyroid individuals by medication dose and 393,101 untreated/euthyroid individuals over 14 years. For those on medication we only included those diagnosed >2 years and who had more than 2 years of tests. For those not on medication we included results from those patients who had a single test or 2 tests with more than 5 years between tests.
Results: The FT4 distribution for levothyroxine treated individuals was similar in shape vs untreated individuals but shifted towards higher FT4 even at the lowest dose of levothyroxine, with an increasing separation of the distributions as levothyroxine dose increased (F value=1.5 increasing to F value=4.2). In contrast the TSH distribution was substantially different for untreated individuals vs those on levothyroxine where the distribution was massively skewed to low/ undetectable TSH with a ‘hockey stick’ configuration, even for those on low daily doses of levothyroxine. For those not on thyroid-hormone replacement, 90% of individuals were within the TSH reference range. For those on medication only 43% were within TSH reference range. For men vs women median levothyroxine dose was higher in all decades, with the highest median daily dose at age 50-59years (men: 107 mg. women 96 mg). Median T4 rose (women>men) and TSH fell progressively (women>men) by age in treated individuals.
Conclusion: We have here described that distribution of FT4/TSH is different in people on and off levothyroxine treatment and that degree off difference increases in treated individuals by levothyroxine daily dose. The distribution of TSH is ‘unphysiological’ even at low levothyroxine dose.
Volume 109
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Endocrine Abstracts
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