Oh Donna, poor Casey, and poor you too because I know you are suffering alongside of him.
Hold on tight, there are still those other test results to come yet. The vet who is treating Casey seems to be very much under pressure (was she the one who was off sick earlier?) so maybe when thats off and she is able to look at the results with a rested and clear eye she will spot something not thought of yet.
And yes, whatever you are doing/do for Casey will be the right thing because it is done with great care and love.

He and you will be kept in my thoughts and prayers and all fingers and paws crossed too.

Love and hugs
Chris