I honestly wouldn't worry too much just yet, especially as your vet said the creatinine was only just above normal. The same thing happened to me with my 4 year old greyhound with a routine blood test ie the vet said he had slightly elevated creatinine. Fortunately, from reading GT, I knew that greyhounds often have a higher creatinine than other breeds and wasn't overly concerned. After discussing this with the vet, he agreed that as the BUN and urinalysis were normal, it was unlikely there was a problem. Some time later, I had his litter sister tested too and her's was exactly the same, so the vet agreed it's just normal for them. I understand that stress (ie vet visit!) can also cause the creatinine to be a little raised too.