[2026 update] Thyroid function tests during substantial weight change posts 61–75
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
The arithmetic in post #61 is right; the assumption feeding it is the part to check.
Two things can be true about Thyroid function tests during substantial at once: the mechanism is plausible and the evidence for the size of the effect is thin. Most of the argument here is people defending the first against attacks on the second.
The confident answers on Thyroid function tests during substantial and the well-sourced answers are not the same answers, which is the most useful thing I have learned reading this category.
Analytical imprecision: any measurement has an error margin. A small difference in consecutive tests is usually measurement noise, not a real change. Knowing the imprecision helps distinguish noise from signal.
Someone should write this up properly, and it should probably not be me.
Post #61 describes the usual case. This is about the unusual one.
Biological variation: the person-to-person variation in a biomarker for a healthy person is larger than most people realize. Comparing your result to the reference interval is one thing; comparing your result today to your result from months ago is more sensitive to change.
Stating my assumptions rather than smuggling them in.
Reference intervals: constructed to contain the central 95% of a reference population, which means one in twenty healthy people falls outside one by definition. Add biological variation and analytical imprecision and the base rate of a meaningless flag is substantial.
One case, stated as one case.
I keep a log for Thyroid function tests during substantial specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing and settled it.
Sensible. I would want the same detail before I acted on it either.
Ask what decision the result would change before ordering it. A test whose result changes nothing is a test that generates worry rather than information.
That is a fair summary of where the discussion has got to.
Fasting state: some lab tests require fasting; others do not. Lipids on a fasting draw differ from lipids on a fed draw. Always note whether the test was fasting when comparing results.
Since Thyroid function tests during substantial keeps coming up, it should probably be a maintained page rather than a recurring thread. I am happy to draft it if someone with more direct experience will review it.
Collapsed as off-topic by two members at trust level 3 or above
Narrowing post #72, because the general version has more than one answer.
Glycaemic markers integrate over different periods. A point glucose and a longer-term marker disagreeing is not a contradiction; it is two different questions.
Two people can read the same figure differently here and both be reasonable.
This topic was referenced in
- Biological variation versus analytical imprecisionClinical › Bloodwork · 2 replies
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