Thyroid function tests during substantial weight change posts 31–60

The failure mode on thyroid function tests during substantial is boring rather than dramatic. It is almost always the step everyone assumes was done correctly because it is too simple to get wrong.

Thyroid function tests during substantial is a question about a distribution, not about a value, and treating it as a value is what produces the confident wrong answers.

Building on post #44 rather than restating it.

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.

Post #46 put the caveat in the right place and I want to underline it.

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.

This follows post #48 rather than contradicting it.

The honest answer on thyroid function tests during substantial is that it depends, and the useful part is the list of what it depends on. Four items, in rough order of how much they matter.

Most people get the first two right and then argue about the fourth.

Quietly grateful for the plain phrasing. Not every thread gets that.

Repeat before acting is standard practice for an isolated abnormal result on most analytes, and it is standard for a reason.

That matches what I was told, which is not the same as knowing it.

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.

Post #52 is right about the mechanism and I think understates the practical bit.

Worth separating thyroid function tests during substantial as a question about the compound from thyroid function tests during substantial as a question about the documentation. They get answered by different people and only one of them is answerable here.

Worth separating two things that post #54 runs together.

I would put moderate confidence on the mainstream reading of thyroid function tests during substantial and no more. That is not scepticism for its own sake; it is where the sourcing actually stops.

A trend needs at least three points to be a trend. Two points are a line and a line through noise is still a line.

That is where I would start, not where I would stop.

Answering the thyroid function tests during substantial question as asked, then the question I think is meant. As asked: yes, with the qualification below. As meant: it depends on how the first measurement was taken.

Following this. I have the same question and no better information than the first post.

TSH and free hormones: TSH is a reasonable screening test but does not tell you about actual free hormone levels. If TSH is abnormal, free thyroid hormones confirm whether there is a real thyroid problem.

The arithmetic in post #57 is right; the assumption feeding it is the part to check.

I disagree with the framing of thyroid function tests during substantial above, and I think it is a substantive disagreement rather than a terminological one. Setting out why, so it can be checked.

The reasoning depends on an assumption that is doing a lot of work and is never stated. If the assumption holds, the conclusion follows. I do not think it holds generally.