Thyroid UK

Thyroid function tests gone from normal to abnormal in 5 months

I have all of the symptoms of hypothyroidism and but have had normal blood tests last year.

Serum TSH 1.650 mu/L (0.40-5.00)

Serum free T4 14.000 mnol/L (10.0-23.0)

I self-treated for 6 weeks with T3, cycling up and back down again, but stopped completely one week before latest blood test. (And in fact I have not started up the T3 again as I was going to concentrate on my adrenals as I did not feel the T3 was providing any benefit.)

The results for this latest test were:

(I had to talk the Dr into testing for T3)

Serum TSH 0.460 mu/L (0.40-5.00)

Serum free T4 8.100 mnol/L (10.0-23.0)

Serum free T3 3.500 mnol/L (3.5-6.5)

My doctor has finally agreed that my thyroid could do with some help and has suggested another blood test to recheck these 3 in case of error or my self-treatment interfering with the result. (I did tell him before that I would self-treat by sourcing my own meds or see a private doctor.)

How my results could go to such extremes is worrying me. Does anyone think that the T3 I took could have had such a dramatic effect on my results?

Also worth mentioning: there was a 'biochemistry comment' at the bottom of the page saying, "TFT's may be consistent with hypopituitarism." My doctor did say something about an endo (not had any mention of one before) during my visit but then just printed off repeat blood test form and said he would ring me with the results in 2 weeks.

Has anyone had experience of this type of thing? I would appreciate your thoughts or guidance. Thank you.

3 Replies

Are you saying they have changed a lot in 5 months because of your FT4 results because if you are then this would be normal if you have been on T3 as your body will not be calling for any T4 if it is getting T3 directly. A low FT4 is often the case when you are taking T3. T4 is called for so that the body can convert it into T3 but when you take T3 directly then the body has no need for T4 so it will stop calling for it and the FT4 levels will drop.

Taking T3 will also lower your TSH quite a lot.

Has this answered your question or was there something else bothering you.

Moggie x


I thought that TSH and T4 production in the body were very slow to return to whatever is normal for the patient, after any kind of thyroid treatment is withdrawn. I've never heard a figure placed on the speed of the return to normal but I would have thought it might take a few weeks?



The TSH response and I believe the fT4 response is likely to be a result of your T3 meds. Even after a week the TSH will still be suppressed. The response of TSH is multiphasic with one part of the response taking, on average, around 6 weeks to stabilise in response to a change. This is why most folk are told to have blood tests 6 weeks after a medication change.

You may need to stay off the meds for a few weeks before having the test repeated.



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