Thyroid function tests during substantial weight change posts 91–120
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Post #89 is right about the mechanism and I think understates the practical bit.
Lipid changes during substantial weight loss are expected and their trajectory is not always monotonic. A single mid-course panel can be misleading.
If anyone has run this properly I would rather read that than my own guess.
One more thing on thyroid function tests during substantial that took me far too long to see: the two figures people quote are not measuring the same quantity. Once you notice that, the apparent contradiction disappears.
Sensible. I would want the same detail before I acted on it either.
Genuine question rather than a rhetorical one: has anyone here actually observed thyroid function tests during substantial, as opposed to read about it? The thread is long and I cannot tell.
Picking up post #97: that is the part I would want checked first.
Adding a reference point for thyroid function tests during substantial. Mine is a single case, collected without controls, and I am posting the method alongside it so it can be discounted appropriately.
Glycaemic markers integrate over different periods. A point glucose and a longer-term marker disagreeing is not a contradiction; it is two different questions.
I would treat that as a working assumption and revisit it.
Agreed on thyroid function tests during substantial, with one qualification that I think matters. The reasoning holds for the case as described. Change the starting assumption and it does not, and the starting assumption is the part nobody states.
I had written a reply contradicting post #97 and deleted it. Here is what survived.
Where I would push back on the thyroid function tests during substantial consensus is the confidence, not the direction. The direction looks right. The confidence is borrowed.
Time of day: some biomarkers vary across the day. Cortisol in the morning differs from cortisol in the evening. Comparing results from different times of day is comparing things that are not the same.
That is the version I would defend. It is not the version I started with.
Adding the measurement that post #101 says would settle it.
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.
I have deliberately not rounded that, because the rounding is where the argument starts.
Where I part company with post #101, and it is a narrow parting.
The practical version of thyroid function tests during substantial is three sentences long. The rigorous version is three pages and reaches the same conclusion with the conditions attached.
Post #105 is the version of this I will quote in future. One addition.
On thyroid function tests during substantial the community has more anecdote than the confidence in this thread implies, and I include my own contribution in that.
Liver enzyme changes during rapid weight loss are commonly reported and have several possible explanations, which is exactly why they need clinical interpretation rather than forum interpretation.
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.
I am confident about the direction and much less about the magnitude.
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.
Old habit: I write down the expected answer before I calculate it.
Collapsed as off-topic by two members at trust level 3 or above
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.
I have said this before in a thread nobody could find, so it is worth repeating.
Post #111 put the caveat in the right place and I want to underline it.
Small correction to my own earlier position on thyroid function tests during substantial. I had the units the wrong way round, which changes the conclusion by an order of magnitude and therefore changes it entirely.
Liver enzyme changes during rapid weight loss are commonly reported and have several possible explanations, which is exactly why they need clinical interpretation rather than forum interpretation.
Before the thread moves on from thyroid function tests during substantial — what is the sample size behind the claim? I am not being difficult; I have seen the same figure quoted from an n of four and from an n of four hundred.
Narrowing post #116, because the general version has more than one answer.
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.
I have left out the parts I could not verify.
Renal function markers: eGFR is estimated, not measured. It depends on creatinine, age, and weight. A small change in creatinine might not mean a real change in kidney function.
That distinction has done more work for me than anything else in this category.
Thyroid function tests during substantial is one of those subjects where the general answer and the answer for a specific case diverge, and the thread will go in circles until someone says which one is being asked for.