I don't know if it is at all relevant but the cat I adopted was found as a stray, he was so emaciated he had collapsed in the street and didn't move for a day, a passerby thought that the 15 year old cat was an abandoned kitten!
He had blood tests and they found nothing wrong with him other than one enzyme being very elevated. i am sorry that i can't remember what enzyme it was but they rechecked his blood after he had spent a night on a drip and then wolfed down a plate of food, the abnormal reading had already dropped. the vet said that the reading was probably down to extreme dehydration and it had largely corrected itself once he was hydrated again.
Could you get the vet to recheck his enzyme levels once he has had time to recover and get some fluid into him? One thing to try is boiling some white fish (like cod fillets) in water its tasty and if slightly warm will smell and so be apetising, its gentle on the stomach and if you leave some of the water in he may lap at the fishy water too. Obviously this isn't possible if he is still at the vet but the drip will do the job of hydrating him whilst he is there.
So glad he was found and you have him home. paws crossed he gets better.
