You said

"Do a pre-surgical evaluation for a kidney removal procedure and then go over everything with the owner."

Nope.  You blew the diagnosis!  Don't feel bad, everyone has missed a diagnosis.  Just learn from it, be humbled by it and try to not rush to a diagnosis in the future.  Being just a little more thorough would have shown you the correct diagnosis.  Good idea to do some pre-surgical tests  but not for a kidney procedure!  What is the VERY NEXT thing you should do?

View the diagnosis here or close this window and go back and try your very next move.