I am glad to hear more clinicians are realising that there are issues with creatinine.
It is elevated from cooked meat meals, as creatinine is the breakdown product of creatine, which is the molecule that transfers energy (ATP) to your muscle so they can contract.
As well, the more muscle you have, the more creatine therefore the more creatinine.
Urea is from the breakdown of protein, so a higher protein diet will also result in a higher urea level. It can also be elevated in dehydration.
He is being quite responsible with your tests, as it is so much easier to slow any renal issues than sort out your kidneys once they are damaged.
I have had high creatine and urea levels on and off, I have even been one of the case studies on grand rounds because of the rapid change in my creatinine levels due to creatine supplementation.
I also just had an elevated creatine after three meals, then being bled.
It sucks you have to protein fast, I would ask if an overnight 10 hour fast is ok with him as well.