My creatinine level was also 500 when I asked to go on PD. I was so tired and sick that I couldn't stand it any more. NOW my creatinine is 800 and strangely I feel great. I guess my body has just adjusted to this level. I can't imagine how great I'll feel when I get my new kidney and my creatinine goes back down!! They can't stop me now, well, just wait!!
When people go on dialysis varies from person to person. My understanding is most people start dialysis when kidney function is 10 percent or less. As to creatinine levels themselves I do not think that is the sole facter in determining when dialysis starts as larger people can have higher levels of creatinine and are not bothered by it. Of course I am in the US and it may be different than where you are. Not sure what the conversion is from 500 to US standards in measurement.
As to having a 800 level and feeling good I think that would be also that other body labs have improved compared to being predialysis. Usually after dialysis starts the albumin comes up and blood counts improve making the patient feel better even though creatinine levels go up.