Comment by vidarh

What does ethnicity has to do with anything?

My creatinine levels are high because my body mass - including muscle mass - is well above average. On the basic kidney tests my GP did, my numbers indicated kidney disease. Doing a Cystatin C test showed very clearly that my numbers were firmly in the normal range.

The page does go on to point out the muscle mass issue:

> The committee highlighted the 2008 recommendation, which states that caution should be used when interpreting eGFR and in adults with extremes of muscle mass and on those who consume protein supplements (this was added to recommendation 1.1.1).

Further down they do mention Cystatin C, and seem to have basically decided that a risk of false positives is acceptable because of a lower risk of false negatives. That part is interesting, and it may well be the right decision at a population level.

But if your muscle mass is sufficiently above average, the regular kidney tests done will flag up possible kidney disease every single damn time you do one, and my experience is that UK doctors are totally oblivious to the fact that this is not necessarily cause for concern for a given patient and will often just assume a problem and it will be up to the patient to educate them.

EDIT: What's worse, actually, is the number of times I've had doctors or nurses try to help me to "game" this test by telling me to e.g. drink more before the test next time, seemingly oblivious that irrespective of precision, making changes to conditions that also invalidates it as a way to track changes in eGFR is not helpful.