SFEBES2025 Poster Presentations Thyroid (41 abstracts)
Evaluating the link between both thyroid stimulating hormone (TSH) and free thyroxine (FT4) both extensively measured mainly in primary care to diagnose, rule out and treat hypothyroidism, using thyroid function test (TFT) results taken from the greater manchester care record 2010-2023
Michael Stedman 1 , Peter Taylor 2 , Buchi Okosieme 2 , Lakdasa Premawardhana 2 , Colin Dayan 2 , Anthony Fryer 3 & Adrian Heald 4
1Res Consortium, Andover, United Kingdom; 2Cardiff University School of Medicine, Cardiff, United Kingdom; 3Keele University, Keele, United Kingdom; 4Salford Royal Hospital, Salford, United Kingdom
Introduction: Over 10 million thyroid function tests (TFT) are undertaken in England annually. To reduce test numbers laboratories often measure TSH and then only reflex measure FT4 if result fall outside TSH reference range (TSH-RR). The relationship between FT4 and TSH results was considered for patients both on and off thyroid medication.
Methods: Simultaneous TSH and FT4 results from 47,869 diagnosed hypothyroid including dose and 393,101 untreated/euthyroid individuals who had been tested once or twice were included.
Results: Of 452,463 results untreated/euthyroid population, 90%(406,700) were within TSH-RR and 99%(448,171) within FT4-RR. As 3,319(83%) of 3,992 with FT4<9 and 175(58%) of 300 with FT4>25 had TSH within TSH-RR, both these groups might not receive a reflex FT4 result. In 407,075 results in the treated population, 176,833(43.4%) were in TSH-RR; this relatively low proportion would then avoid FT4 reflex testing. The discrepancy between TSH and FT4 could be missed including 1,368(15.1%) of the 9,068(2.2%) with low FT4<9 that had had low/normal range TSH<4.0 and the 3,065(21.7%) of the 14,123(3.5%) with high FT4>25 with TSH in RR. These effects were more prevalent in people taking lower dose levothyroxine. Treated individuals were almost 40-times more likely to have a high FT4 despite a normal TSH than untreated individuals.
| TSH (mu/l): FT4 (pmol/l) | FT4<9 | FT4-RR:9-25 | FT4>25 |
| UNTREATED:TSH<0.4 | 48 | 13,146 | 115 |
| UNTREATED:TSH-RR 0.4-4 | 3,319 | 403,206 | 175 |
| UNTREATED:TSH>4 | 625 | 31,819 | 10 |
| TREATED:TSH<0.4 | 201 | 92,574 | 10,195 |
| TREATED:TSH-RR 0.4-4 | 1,368 | 172,400 | 3,065 |
| TREATED:TSH>4 | 7,499 | 118,910 | 863 |
Conclusion: Given risks associated with prolonged exposure to high and low FT4 levels and importance of dose adjustment, it’s clear that both FT4 and TSH should both be measured, especially for those treated with levothyroxine. This difference in TSH–T4 relationship by treatment status needs urgent attention.
Volume 109
Article tools
My recent searches
My recently viewed abstracts
Authors
Endocrine Abstracts
ISSN 1470-3947 (print) | ISSN 1479-6848 (online)
© Bioscientifica 2025 |
Privacy policy |
Cookie settings
BiosciAbstracts
Bioscientifica Abstracts is the gateway to a series of products that provide a permanent, citable record of abstracts for biomedical and life science conferences.
Find out more