From the other side of the consultation, briefly. The version of this that has an answer is narrower than the version being asked. Narrow it and it becomes tractable; leave it broad and the thread will produce nine confident and incompatible replies.

Worth separating that from renal function, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.

Happy to go further on any of that.

One thing that is still open after james_edin’s answer:

How to read eGFR during rapid weight loss, given that creatinine depends on muscle mass and muscle mass is changing?

Dr.EndoIndy said:

The version of this that has an answer is narrower than the version being asked.

Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. This treats a plausible mechanism as a demonstrated one. Plausible is where you start looking, not where you stop.

That is the short version; the long version is somebody else's post.

Dr.EndoIndy said:

The version of this that has an answer is narrower than the version being asked.

That is right for the common case. Whether it is right for the case being asked about depends on a detail that has not been given.

Moderator note: reminder that nothing in this thread is medical advice, and that clinical claims need a source.