Thyroid UK
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Stress/anxiety and blood test results

I hope someone out there can explain to me if high cortisol levels could affect the results of thyroid function blood test.

I was tested recently and was very surprised how much the readings had changed from last year. August 2014 - TSH: 1.8 (0.27 - 4.20), T4: 18.6 (12.0 - 22.0), T3: 3.8 (4.0 - 6.8). March 2015 - TSH 0.55, T4 25.3 (same ref: ranges) do not have T3. The only change was that I increased my thyroxine by half a 25mcg 3 months ago. I wouldn't have thought that such a small increase would have made that much difference to readings.

However, looking back over the recent blood test I was going through a very bad time of anxiety, insomnia and depression on and off since December last year and which went on for 2/3 weeks prior to and right up to the time of testing. (I hadn't slept the night prior to blood test). I gathered some information from comments here I've noticed that stress and in particular ongoing stress, etc. affects cortisol levels. What I would like to know is would this affect my blood test results too and to such a degree as above?

I have been told that I'm probably not converting well and so I am in the process of seeing an Endo. But I would really be interested in knowing if my stress/anxiety would have affected test results. I would appreciate any comments on this.

1 Reply

Mischa, a guess only, stress affects so many things I wouldn't be surprised if high stress affected thyroid levels. Stress can be trigger for thyroid disease.

12.5mcg is a small increase but can significantly affect thyroid levels, as it has yours. You need a FT3 reading to determine whether or not you are converting well. Low TSH + high FT4 with low FT3 indicates a lack of conversion. You can order private FT3 tests from Blue Horizon and Genova via


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