Why some thyroid cancer patients still have high TSH even on medicine
High TSH levels during TSH suppression therapy in DTC postoperative patients are associated with low DIO2 expression in the thyroid and impaired thyroid hormone sensitivity
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
After having their thyroid removed, patients take thyroid hormone pills to keep TSH low and stop cancer growth — but some still have high TSH. This study found their bodies can't convert the pill's hormone (T4) into the active form (T3) well, and their brain doesn't respond properly to the hormone levels.
Surprising Findings
Patients with high TSH had lower FT3 levels even when their FT4 was supraphysiological (above normal range)
Common belief: high FT4 = high FT3. This study shows the conversion system is broken independently — so more pills don’t fix the problem.
Practical Takeaways
If you're on levothyroxine but still fatigued with high TSH, ask your doctor for FT3, FT4, and TSHI tests — you might need T3 supplementation.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
After having their thyroid removed, patients take thyroid hormone pills to keep TSH low and stop cancer growth — but some still have high TSH. This study found their bodies can't convert the pill's hormone (T4) into the active form (T3) well, and their brain doesn't respond properly to the hormone levels.
Surprising Findings
Patients with high TSH had lower FT3 levels even when their FT4 was supraphysiological (above normal range)
Common belief: high FT4 = high FT3. This study shows the conversion system is broken independently — so more pills don’t fix the problem.
Practical Takeaways
If you're on levothyroxine but still fatigued with high TSH, ask your doctor for FT3, FT4, and TSHI tests — you might need T3 supplementation.
Publication
Journal
Frontiers in Endocrinology
Year
2025
Authors
Jialu Wu, Juan Huang, Zhe Yan, Anqi Yuan, Yifei Song, Hui Huang
Related Content
Claims (6)
In patients who have had their thyroid removed and are taking levothyroxine, those with high TSH levels despite high FT4 levels show reduced activity of an enzyme that converts T4 to T3, lower T3 relative to T4, and increased sensitivity to thyroid hormones in the brain, suggesting a biological mechanism may limit the effectiveness of hormone replacement therapy.
In patients who have had their thyroid removed and are taking levothyroxine, those whose TSH levels remain above 2.0 mU/L show higher indicators of reduced pituitary sensitivity to thyroid hormones in the blood.
A blood test called the thyroid-stimulating hormone index (TSHI) can moderately predict which patients continue to have high TSH levels after thyroid removal and levothyroxine treatment, even when the treatment dose is considered adequate.
In patients who have had their entire thyroid removed due to thyroid cancer, the amount of type 2 deiodinase enzyme present in remaining thyroid tissue is lower when thyroid-stimulating hormone (TSH) levels are high (above 4.2 mU/L) than when TSH levels are low (below 2.0 mU/L), even when thyroid hormone levels in the blood are normal.
After thyroid removal, some patients have high TSH and high FT4 but low FT3, which suggests their bodies are not efficiently converting the available thyroid hormone (T4) into its active form (T3).