How Does Thyroid Hormone Profile Differ on and Off Replacement Treatment?
Authors' conclusion
The current treatment regimens of either low or high dose levothyroxine are not delivering the expected laboratory TFT profiles, with significant numbers of treated patients being well outside the expected values: both TSH and FT4 being significantly higher. This effect appears to be more prevalent in women than men.
Study context
- Population
- People with thyroid function test (TFT) (free T4 (FT4)/thyroid-stimulating hormone (TSH)) from General Practices, Salford Royal Hospital laboratory, 2009–2012after filtering
- Participants
- 12,006 vs 43,394
- Exposure
- LT4-treated vs untreated
- Treatedn = 12,006
- Untreatedn = 43,394reference
- Outcome
- Percentage of patients outside the ellipse (5%/95% percentiles of log TSH and FT4)
Methodological detailssingle-centre, cluster analysis, General Practice samples only, Total data set: 290,000 tests on 130,000 individuals; treated patients had 43,846 test results
- Single-centre
- Cluster analysis
- General Practice samples only
- Total data set: 290,000 tests on 130,000 individuals; treated patients had 43,846 test results
Main finding
As reported in the abstract
| Group | Value | FT4 median | Outside untreated 5%/95% percentiles | Outside treated 5%/95% percentiles | Outside untreated limits |
|---|---|---|---|---|---|
| Untreated | median 1.8 mU/L | 15.5 pmol/L | 24% | ||
| Treated | median 2.3 mU/L | 18.9 pmol/L | 22% | 68% |
Value
Untreatedmedian 1.8 mU/L
Treatedmedian 2.3 mU/L
FT4 median
Untreated15.5 pmol/L
Treated18.9 pmol/L
Outside untreated 5%/95% percentiles
Untreated24%
Treated— not stated in the abstract
Outside treated 5%/95% percentiles
Untreated— not stated in the abstract
Treated22%
Outside untreated limits
Untreated— not stated in the abstract
Treated68%
- Treated vs untreated median TSH
- +30%
- Treated vs untreated median FT4
- +22%
Observational data: associations, not effects.
Further findings
Treated results outside untreated limits, by sex and age
- Male
- 63%
- Female
- 70%
- Age < 60
- 67%
- Age ≥ 60
- 64%
Original publication
How Does Thyroid Hormone Profile Differ on and Off Replacement Treatment? Clin Endocrinol (Oxf). Published 19 December 2024. doi:10.
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