OUDE Hypoforum

TWENTY-FOUR HOUR HORMONE PROFILES OF TSH, FREE T3 AND FREE T4 IN HYPOTHYROID PATIENTS ON “COMBINED T4/T3” THERAPY.
(1)Siddique H, (1)Saravanan P, (1)Simmons DJ, (2)Greenwood R, (3)Peters TJ, (1)Dayan CM. (1)University Research Centre for Neuroendocrinology, University of Bristol, Bristol, United Kingdom, (2)RDSU, Bristol Royal Infirmary, Bristol, United Kingdom, (3)Dept of Primary Care, University of Bristol, Bristol, United Kingdom
Background & Aims: The 24-hour hormone profiles of hypothyroid patients treated with T4 alone or T3 alone are well known from careful studies performed over 20 years ago. However, following a recent report, there has been interest in the use of a combination of T3 and T4 to improve psychological well-being in patients on thyroid hormone. Methods: A subgroup of 20 patients [10 on combined T4/T3 (study,S) & 10 on T4 alone (controls,C)] was randomly selected from the 697 patients who were already involved in the WATTS study. The study group received 10mcg of T3 in place of 50mcg of T4 while the dose of T4 in the control group remain unchanged. All the patients had been on their study medication for a minimum of 3 months. 12 blood samples were collected for FreeT3, FreeT4 and TSH at times 0,1,2,3,4,6,8,10,12,14, 16 22 and 24 hours post dose.Results: Basal free T3 levels were similar between the 2 groups (S:C 4.43:4.69 pmol/L, p = 0.31) but basal free T4 (S:C 12.1:17.9 pmol/L, p = 0.001) and TSH (medial S:C 3.1:0.7 mU/L, p=0.01) were significantly different: Profiles of all 3 hormones were very stable over the 24 hour period on T4 alone but free T3 levels showed a rise of 40% within the first 4 hours after taking the medication in the group on combined treatment and mean free T3 levels remained higher than T4 alone for 16 hours. Free T3 levels at 3hours post-dose were significantly higher in the T4/T3 group (S:C 6.34 vs 4.63 mU/L, p < 0.001). Conclusions: Despite chronic combined T4/T3 therapy, wide trough-to-peak variation in free T3 levels was present in patients on combined T4/T3 therapy but not on T4 alone.
Poster presentation at the 23th ETA in Scotland European Thyroid association