Thyroid UK
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Help with blood tests. Does free T4 fluctuate?

Hi I've posted on here before and people have been really helpful. Had bloods done through GP in early Aug and TSH was 1.4 and fT4 was 12.9 (range 12 -22).

Had bloods done again in Sept through private endo. TSH was 1.12, free T4 was 12.3 (same range) and free T3 was 3.4 (range of 3.1 - 5.8).

Went to see an ophthalmologist who said symptoms (dry, bloodshot eyes with swelling underneath) suggested thyroid eye disease. Had blood tests again in October. This time TSH was 1.38 and fT4 was 11.6 (range of 9.0 - 22). (Didn't do fT3 this time.) Got referred to second private endo who asked me to do bloods again(!). Just got told the results and told TSH was 0.98, fT4 was 10.5 (range of 9.0 -22), but free T3 was over 4 this time (waiting to be emailed results).

Does anyone know if your free T4 can fluctuate? I understand that TSH can be lower first thing in the morning before eating and this may explain the last result.

Should I be concerned by decreasing fT4?

I've mentioned secondary hypo to endos but they think unlikely given all other blood results appear normal. Is there anything else I should be insisting they check?

4 Replies

I have been Hypo for over 30 years and have always been prescribed Levo. I kept note of results this 15years or so. The T4 can go up and down surely. My lowest level being 20.02 and highest being 34.3

TSH can fluctuate worse in my experience

Lowest. 0. 53

Highest. 73.35

At 1 stage both readings were in the early 20,s. Your T4 seems low hollyt.

Other people on here will keep you right. What medication are you on? I am seriously thinking of going down the NDT or T3 road but I have to do a lot of learning before that.

Jose651 x


Hi Jose

Thanks for the reply. I'm not on any medication. Trying to find out what is causing some unexplained symptoms. As results all within range and TSH is low doctors are saying they won't make a diagnosis of hypo, even though that is what symptoms are pointing to. I wouldn't mind, but they are not coming up with any suggestions as to what the problem is if it isn't a thyroid issue!


Hollyt, when FT4 drops TSH should rise. NHS won't usually make a diagnosis of primary hypothyroidism until either TSH is over range, or FT4 is below range. Falling FT4 is a problem and as your TSH isn't rising in response, it indicates secondary hypothyroidism or isolated TSH deficiency if other pituitary hormones are normal.


I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.



You might find this earlier post of interest:

We must all realise that biological factors do tend to vary over time - within a day, and across every timescale. They results of tests also vary - whether intrinsic variability in the test itself and the procedures surrounding it, between labs, etc.

The value of a snapshot measurement must always be questioned. But it is all we have much of the time.

If I were you, I'd create a nice little graph of the results. Time along the bottom and numbrs upwards. You can do that on paper or use numerous programs such as Excel. When you do that, you might more readily see what is happening.


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