Blood test fasting or not?

Hehe! I have a fasting blood test, TFT, vitD, B12 & folate for GP who reduced Levo at my request and I've been a leetle bit concerned endonob will castigate him as it's no longer suppressed.

So, after the fasting test I shall stop off for steak and chips then onto the hospital for endo's TFT & thyroglobulin. Such a pity one set of tests can't do all, but the systems don't speak to each other and GP can't get FT3 & FT4! Still, it'll be interesting to compare TSH taken hours apart, pre and post fasting.

Must remember to take levo before bed tonight too. Reverse usual advice to suppress TSH.

Sorry to hijack but I've also read the opposite about fasting so I'm a little confused...

This an extract from this page tiredthyroid.com/tsh.html

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...