Thyroid UK

Opinions needed re: fasting before TFTs

I started talking about this on another thread but thought I should start my own to get other people's opinons on the matter.

In this thread Clutter and Shaws posted a link to a very helpful page that explains that you should test as early as possible in the morning and that you shouldn't take your medication before the test but it also says that eating before a test can reduce your TSH.

This is the link

A few days ago I had found the opposite suggestion on this site It's a lot of reading so here's the bit that I am talking about which is sort of half way down the page

"TSH decreases when fasting. [17] Most patients do their lab tests in a fasting state, because other labs like glucose and cholesterol require it. But this may result in an artificially low TSH that does not reflect true thyroid levels. In fact, TSH has a circadian rhythm, with a peak around midnight (with much variability between individuals), and a low in the afternoon; fluctuations are normal. The change in TSH from peak to trough is approximately 72%. Free T3 levels also show a similar circadian rhythm (with a smaller amplitude) with a time lag of approximately 90 minutes behind the TSH curve. The Free T4 curve did not follow the TSH curve at all. [18] Labs drawn in the morning could be significantly different from labs drawn in the afternoon after lunch, with one TSH in "normal" range and the other in the hyperthyroid or hypothyroid range..."

So I'm really not sure which one to believe. I know that tsh is unreliable but unfortunately our doctors insist on using it as the tool to diagnose thyroid problems.

All I can go by is the two tsh tests I have had done

First one: 10.30ish am 1.4 FASTING

Second one : 9.10am 3.4 NOT FASTING

What are other people's experiences when having their tsh tests done?

5 Replies

bumping for opinions :)


Sorry I don't know the answer but would be interested to hear what other people have to say too xx


Damn, hoped there'd be clarification by now.

I had TFT at 11.10 via GP and TFT & Tg at 1.30 via hossie today, both fasting. Won't have hossie results until I see endonobess Monday though. Lunch following was disappointing. Have been eating Mars bars to compensate.


Let us know your results Clutter. Sorry lunch was disappointing (excluding the mars bar!)

Anybody else have any thought on this contradicting information?


Bumping one last time in the hope that someone will give their opinion.


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