Hi Arlene-
One thing you might try before all the testing is to put him on a corn-free diet. Many cats cannot tolerate corn. I would take him off of all food overnite and give him only Gerber Baby meat (turkey or chicken) for 24 hours. See if his stool firms up with that. If it does, you may have a cat that just can't eat anything with corn. Innova, Wellness and Felidae are all foods that do not contain corn. You can try putting a little of the dry food in with the Baby Meat to see what happens. If the stool gets runny right away, then there is something else going on. I have a good friend with a boy that can only eat Rabbit. She has to order his food from www.petfooddirect.com, but since going on the rabbit and barley (or it may be rice, I'm unsure) - he has had firm stool ever since.
Please let me know if the above helps. I would try anything before going through a lot of expensive testing with the stress involved.
Please Press ACCEPT if my answer helped solve your problem.
Lori McLaughlin
Your veterinarian should ALWAYS be consulted first and foremost when your pet's welfare is at stake.