SFEBES2026 Poster Presentations Thyroid (34 abstracts)
The change in thyroid hormone profile pre- and post- initiation of levothyroxine: an evaluation of longitudinal thyroid hormone profile over time
Michael Stedman 1 , Peter Taylor 2 , Ian Halsall 3 , David Halsall 3 , Buchi Okosieme 2 , Suhani Bahl 2 , Sangeeth Veluchamy 4 , Nadia Ruzdhii 5 , Lakdasa Premawardhana 2 , Colin Dayan 2 , Anthony Fryer 4 & Adrian Heald 4,6
1Res Consortium, Andover, United Kingdom; 2Cardiff University School of Medicine, Cardiff, United Kingdom; 3Addenbrooke’s Hospital, Cambridge, United Kingdom; 4Salford Royal Hospital, Salford, United Kingdom; 5Keele University, Keele, United Kingdom; 6University of Manchester, Manchester, United Kingdom
Introduction: Optimizing thyroid hormone status in hypothyroid individuals remains a subject of considerable debate. Over 10 million thyroid function tests (TFTs) are performed each year in England, the majority requested in primary care. This study aimed to investigate how thyroid hormone levels evolve in the years preceding and following the initiation of Levothyroxine (LT4) therapy in patients with primary hypothyroidism.
Methods: Using comprehensive city-wide population health records, we analysed TSH and FT4 results from 2012–2023 (12 years) for individuals diagnosed with primary hypothyroidism who commenced LT4 treatment between 2015–2019. Their TFT results were compared across the years before and after LT4 initiation. Only patients with more than five TFTs during the study period were included. Reference ranges relevant to diagnosis were defined as TSH ≤4.2 mIU/l and FT4 ≥12.0 pmol/l.
Results: In the years prior to starting LT4, TSH increased progressively, indicating declining thyroid function. Following initiation, TSH levels fell rapidly to values equal to or below those observed several years before diagnosis (3.1 vs historical 3.5 mIU/l). The average daily LT4 dose rose steadily from 49 mg at initiation to 69 mg/day after seven years, accompanied by an increase in median FT4 from 13.0 to 16.1 pmol/l. From the end of the first year of treatment, FT4 levels remained consistently higher than pre-treatment values. By age 50, 60% of women and 50% of men had commenced LT4 therapy, reflecting earlier onset in women. Individuals aged ≥60 years had higher TSH levels than younger adults, both before and after treatment.
Conclusion: This population-based analysis demonstrates diverse treatment responses and a trend toward increasingly “unphysiological” TFT profiles following LT4 initiation. The continued rise in both FT4 and LT4 dose suggests that ongoing adjustments may often reflect perceived lack of benefit rather than biochemical necessity.
Volume 117
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Endocrine Abstracts
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