How Accurate is Estimated Global Filtration Rate with Higher Muscle Mass?

Hi guys, I’m not sure where to ask this but as the TRT crowd are used to reading blood results, I thought id ask here, also I am on TRT too.

I’ve been wondering about muscle mass and increased creatinine levels, most blood tests estimate kidney function (egfr) by using this result and a formula.

My Creatinine levels are always near the upper limit, the EGFR used on my bloods always shows it is low, which could indicate kidney issues, but I’ve found another formula which is catered more to people with a higher muscle mass and this brings my EGFR into normal ranges but I’m wondering if anyone here with more knowledge in this area could tell me just how much muscle mass and muscle breakdown from training increases creatinine levels and if these higher levels are harmful or indicative of a kidney issue?

Stats - age 29 - 180cm - 86kg - 11% BF
recent tests have put my creatinine levels at
100 umol/L - range (59 - 104)
and also
122 umol/L - range (59 - 104)

Cystatin C test would be more accurate (or rather less fraught) when assessing kidney issues in someone with greater muscle mass. While creatinine numbers skew up dramatically for those who are more muscular, Cystatin C seems to have no such correlation.