Serum Thyrotropin and Triiodothyronine Levels in Levothyroxine-treated Patients
Authors' conclusion
In LT4-treated patients, the relationships between serum FT4 vs TSH and FT4 vs T3 across a range of FT4 levels are disproportionate. As a result, dose changes in LT4 that robustly modify serum FT4 and TSH values may only minimally affect serum T3 levels and result in no significant clinical benefit.
Study context
- Population
- Adults aged ≥18 years treated with levothyroxine (LT4), from a large clinical database, January 1, 2009, to December 31, 2019; subdivided by serum free thyroxine (FT4) level
- Participants
- 9,850 adults
- Outcome
- Model fitting of the relationships between serum FT4 vs TSH, FT4 vs T3, and FT4 vs T3/FT4
Methodological detailsobservational
- Observational
Main finding
As reported in the abstract
Relationships of FT4 with T3, TSH and T3/FT4
FT4 linearly associated with T3 until an inflection point at FT4, then flattening of slope (convex quadratic curve)
0.7 ng/dL
Observational data: associations, not effects.
Original publication
Serum Thyrotropin and Triiodothyronine Levels in Levothyroxine-treated Patients. J Clin Endocrinol Metab. Published 14 December 2022. doi:10.
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