eGFR fluctuation and the creatinine denominator problem — the long version — setting out what I have, and where I think it stops being reliable.
A narrow question about egfr fluctuation, deliberately narrow, because the broad version has been asked here four times and produced four long threads and no answer.
One question, stated units, stated method, and what I have already ruled out.
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.
I am aware this is the third time this month I have made this point.
Adding the measurement that post #3 says would settle it.
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.
I had written a reply contradicting post #3 and deleted it. Here is what survived.
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.
One caution on egfr fluctuation: everything above assumes the underlying documentation is what it claims to be. That assumption is doing real work and is rarely stated.
The version of egfr fluctuation that I was taught turned out to be a teaching simplification. Useful, and not true in the way I had assumed it was.
Picking up post #8: that is the part I would want checked first.
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 would rather post the uncertainty than round it away.
Quietly grateful for the plain phrasing. Not every thread gets that.
If someone has run egfr fluctuation properly I would rather read that than my own reconstruction of it. Posting mine only because the thread has gone quiet.
Repeat before acting is standard practice for an isolated abnormal result on most analytes, and it is standard for a reason.
This follows post #13 rather than contradicting it.
Taking egfr fluctuation seriously for a moment rather than deflecting: the honest position is that the community has observations and no controlled comparison, and those two things support very different sentences.
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.
Egfr fluctuation is well covered in the tag pages, and the older discussions are better than the recent ones because they were argued out properly. Worth twenty minutes before adding to this one.
The reason egfr fluctuation keeps being re-asked is that the answer is conditional and people quote it without the condition. It is not that the answer is unknown.
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.
I would call the community position on egfr fluctuation likely rather than established, and I would be comfortable defending that hedge.
Egfr fluctuation has a well-known answer and a correct answer, and the interesting work is establishing that they are the same. Nobody has done that here yet.
Glycaemic markers integrate over different periods. A point glucose and a longer-term marker disagreeing is not a contradiction; it is two different questions.
Everything in post #19 holds. The case it does not cover is the one I have.
Reframing egfr fluctuation slightly, because I think the disagreement is about the question rather than the answer. If the question is "does it happen", yes. If it is "how often", nobody here knows.
Narrowing post #23, because the general version has more than one answer.
Something worth flagging about egfr fluctuation: the strongest-sounding claims in this thread are the ones with no source attached, which is the usual pattern and not a coincidence.
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.
The interesting part of this is the exception, and I do not understand the exception.
Glycaemic markers integrate over different periods. A point glucose and a longer-term marker disagreeing is not a contradiction; it is two different questions.
Worth one more sentence than it usually gets.
Answering the question post #23 raises rather than the one it answers.
The claim about egfr fluctuation upthread is stronger than its source supports. I have read the source. The source says "associated with" and the post says "causes".
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.
Same conclusion as the reply above, reached differently, which is mildly reassuring.
Post #27 is the version of this I will quote in future. One addition.
Two sentences on egfr fluctuation and then I will stop, because the rest is speculation and the thread is better without mine.
What is documented is narrow. What is inferred from it is broad. The gap between them is where every argument here lives.