PCP's know a little about a lot of stuff. They're great resources to have. But if you have a concern and need to dig deeper into a subject, PCP's just don't cut it. I'm fortunate that I have a PCP that knows what he knows, but isn't afraid to refer me to a specialist if he is not certain about something. I had microscopic traces of blood in my urine at a routine blood test. My PCP ordered a CT scan, assuming it would come back that I had a kidney stone. It came back as suspicious for kidney cancer. He immediately got me a referral to a wonderful urologic oncologist. I got it taken care of when it was extremely small and the surgeon said I should have no recurrence.
That's a long, convoluted story, but the moral of the story is if you're concerned about the creatinine level, have your PCP get you a referral to a good urologist.