This article is more than 5 years old. Information may no longer be current.
TSH, free T3:T4 ratios increased after discontinuation of levothyroxine
Data from a small pilot study indicate that short-term withdrawal of levothyroxine was associated with higher plasma thyroid-stimulating hormone levels and an increased free triiodothyronine to free thyroxine ratio.
Researchers included 13 patients treated with monotherapy levothyroxine whose treatment was temporarily discontinued for 1 week, according to Martin Carlwe, MD, of the department of medicine at Halland County Hospital in Halmstad, Sweden, and colleagues.
“Within 3 days after discontinuation of levothyroxine, a significant trend was noted. Our results suggest that there is a direct correlation between TSH levels and the conversion of the free T4 to free T3. Since treatment of hypothyroidism lowers TSH, it may be an explanation for why patients with replacement therapy have a free T3/T4 ratio that is lower than healthy controls,” the researchers wrote.
In the 13 patients studied, significant systematic changes were observed in free T3:T4 levels (P<.001), and median free T3:T4 increased from 0.23 pmol/L to 0.28 pmol/L, according to researchers.
Similar data indicate a rise in TSH levels (P<.001) across the observation points (baseline, days 3, 6 and 7). Median TSH increased from 0.6 mU/L to 4.64 mU/L during the study, researchers wrote.
In particular, there was a significant increase in T3:T4 levels between days 3 and 6 (P=.05); TSH levels between baseline and day 3 (P=.004); and days 3 and 6 (P=.004).
Disclosure: The researchers report no relevant financial disclosures.