The other day, and purely out of interest, I used the NHS app to read up about Propranolol (P). I could not believe that I have been prescribed a drug that interferes with Thyroxine (T) uptake. P was prescribed by Consultant who was made aware of existing medications.
GP has requested lowering of fT4 due to very low TSH. fT4 has been lowered from about 20 to 16 with a minimal increase in TSH. However, I am of the opinion that my metabolism is running more slowly than perhaps it should, and has been for many years. I do not relish the thought of reducing T from current 200mcg per day.
Now, my understanding is that T4 is converted to T3. What I would be interested to know is what triggers an increase in TSH.
Also, is there any alternative to P that does not interfere with T4 conversion to T3?
Another question, is there a typical ratio between fT4 and fT3? I ask as on the only occasion that both were tested from the same sample, fT4 was approx. 7.5 times the value of fT3.
Thanks for reading this far,
Eccleston
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Eccleston
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Propranolol blocks type-1 deiodinase, one of the two enzymes that convert T4 to T3. It is used in hyperthyroidism to reduce thyroid hormone activity. Obviously it is not appropriate to hse it in hypothyroidism. Most doctors are probably not aware of this but endocrinologists certainly should be There must be suitable alternatives but I have no cardiac knowledge and can't suggest any. If you discontinue Propranolol you will probably do fine on a lower dose of thyroid hormone. Make sure they don't give you amiodarone as that is even worse for thyroid patients.
The pituitary uses type-2 deiodinase and so is unaffected, hence the high doses of levothyroxine will suppress TSH even though the rest of the body tissues will have varying degrees of hypothyroidism.
Hi, Thanks for your message. I appreciate you giving your time to respond. Have noted your comment about amiodarone. Will tackle GP within the next few days.
“GP has requested lowering of fT4 due to very low TSH”
lowering ft4 should “make” the TSH rise. But it a terrible reason to because the TSH doesn’t always respond (as you’ve seen) & you’ll be hypo with too low a FT4.
Do you have TSH, FT4 & FT3 results with lab ranges? Add if you do.
TSH should respond to both T4 & T3 levels & is part of the feed forward - feedback process - the higher the TSH - the higher conversion tends to be. It’s about preserving FT3 levels.
Ratio between fT3:FT4 usually something like 1:3. but isn’t the best method to look at thyroid hormones. Better to look at % through range. FT4 is often 10 - 15 % higher in range than FT3. Which is why most feel well with FT4 in top 3rd of range & FT3 over 50%.
Also unsure what alternative beta blocker would be recommended, but do not stop propranolol suddenly (or quickly). Must be done gradually. Sometimes very gradually. A specialist abruptly stopped a 3x40mg daily dose. They should have known better & I had no idea. Was unwell with migraines for over a fortnight, before the GP realised what had happened & put me back on them - permanently. Slowly reduced dose, but still take them.
Hi, Thanks for your comments, they are appreciated.
For info, my latest TFT showed TSH 0.80 mIU/L - Range 0.27-4.2
and fT4 as being 15.6 pmol/L within the range 12.0-22.0
In Nov 2023 TSH was 0.11 and fT4 19.6 These results led to the request from GP to reduce medication.
During the period May 2010 to date fT4 has hovered around 20 with outliers being 16.0 and 27.8. Over the same period TSH has ranged from <0.05 to 1.24 but, during 2014 readings of 14.68, 13.4, 18.07 and 13.64 were recorded. fT4 did not appear to be affected significantly by these high results. This led to a visit to the hospital consultant where a whole series of blood tests were made where, for the only time I am aware fT3 was measured.
The results are as below:
Further to your recent outpatient appointment, I now have the results of your recent blood tests.
Thyroid function from 30th January showed sodium 141, potassium 5.1, creatinine 81, bilirubin 15, ALT 104, ALP 111, albumin 45, free T4 of 24.1 (reference range 12-22), TSH 5.65 (reference range 0.27-4.2). Blood tests done elsewhere showed free T4 21.7 and TSH 5.37 and T3 analysed at another Hospital 3.3. 9am cortisol 458, FSH 14.0, LH 9.5, prolactin 165, total testosterone 6.7, PSA 3.1
ln keeping with my clinical assessment, you have been over treated with Levo-thyroxine. The blood tests do confirm that your thyroid hormone levels are on the high side. ln the first instance, I recommend you reduce the dose of Levo-thyroxine to 225prg once daily and I have copied this letter to your GP so he is aware. An incidental finding is that your testosterone level is low. (levothyroxine intake prior to tests 250mcg daily).
On the subject of 'the higher the TSH - the higher conversion tends to be. It’s about preserving FT3 levels.' as you stated, it suggests to me that there needs to be a 'fine tuning' of each of the TFT values to obtain the best outcome.
Another member, SlowDragon has advised re Propranolol and provided some links for me to explore.
Hi, Thanks for giving your time to respond. Propranolol was prescribed to treat Portal Hypertension manifesting itself as varices (in the stomach) as noted following a gastroscopy. Will follow the links later.
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Not sure what my tests are showing???
Help with test results please: T3 only, why is TSH not higher if FT3 and FT4 below range?
Agh…Whats going on with me? 
Thyroid hormone homeostasis in levothyroxine-treated patients: Findings from ELSA-Brasil
Lab Results - High T3!
