You could be right as I’m aware of a study on diabetics that showed no significant difference although there was a slight increase in the mean.
Here’s the study that shows 300g boiled beef increased serum creatinine albeit older which led me to believe that there is a basis. As noted - the suggested culprit is creatine intake but they didn’t explicitly prove it:
Personally, I’ve also had increases in creatinine compared to when being off it for a month (i.e. forgot to bring it on a trip), which was also the case for my partner. It does appear to have a difference for me over 2 tests. There could be confounders or individual differences of course.
I took 10g of creatine in a smoothie before I went and had an MRI, and the radiologist refused to inject the contrast because he insisted i was in renal failure, even though I told him my creatinine was high because of the creatine. I found support in the literature for acute increase in creatinine after creatine supplementation, (which makes perfect sense since it’s a breakdown product of creatine, especially with a 10g dose which was unnecessarily high), although I don’t have time to find the reference at the moment. My creatinine is always a bit high, but eGFR from cystatin C is excellent.