Just sat reading the "UK Guidelines for the Use of Thyroid Function Tests" as formulated by the Association for Clinical Biochemistry (ACB), the British Thyroid Association (BTA) and the British Thyroid Foundation (BTF)…..I really should get out more often.
Pondering the whole TSH as a measure of thyroid function controversy, I was interested to see that the guidelines do acknowledge that “the secretion of TSH is pulsatile [brilliant word – means beating rhythmically!.... by that I think they mean it has a circadian rhythm] and night time concentrations are higher than during the day”. I did in fact know that already and recently read elsewhere that there is a 72% variation between your night-time TSH and that during the afternoon.
If this is the case, not only does it have important implications for when we as thyroid patients go for our blood tested (I always fix my appointment first thing in the morning). More importantly, however, are the implications of this for the labs when testing subjects to determine reference ranges. The guidelines go on to state that:
“For TSH, reference ranges should be established using specimens collected between 0800h and 1800h”,
- which is quite a wide window of time considering its “pulsatile” nature (I am going to try and use that word at least twice daily this week!). Surely collection times, at the very least, should be standardised between labs???? It raises all sorts of questions like do they take the blood samples to establish their reference ranges at staggered intervals during the day to compensate for its “pulsatile” nature (.....doing well!) or do they simply call their subjects in all at the same time?
Am I missing something? As far as I can see, this state of affairs could potentially result is quite a variance between different labs. Are you out there Helvella, Diogenes….PR4NOW…. and the like….have you any thoughts on this? Considering it’s pulsatile nature (hat-trick!) and the wide range of its variation and the fact that we are dealing with tiny hormonal shifts correlating with symptoms I would have thought it was of paramount importance to have this more closely pinned down.
Thoughts/observations/corrections much appreciated.