Hello and welcome to Just Answer. I am a licensed veterinarian and would be happy to answer your questions.
What do you mean by "the blood tests are positive"?
How long has this been going on?
My cat is 14 years old, at least. He has been in good health till October of last year, when he started to throw up more than usual. Lately it has been a brown liquid. Also, we took him to the Vet, and he was given liquids because he was dehydrated, and had lost weight. His health returned better than ever. He also was given antibiotics, long term. Now, he is throwing up again, and we have tried changing his food to Canned and different types of dry.
The vet did several tests on his blood, and could find bothing wrong
Have any imaging tests been run like xrays or ultrasound?
This is a very common scenario in older cats and it is likely that there is disease present, but that it is hiding very well. Most of the time with the symptoms you describe, the most likely location of the problem is the GI tract.
What should we do? Return to the Vet?
Many cats have a low grade chronic pancreatitis and it is difficult to prove or confirm. It is uncertain how much this disorder comes into play in the decreased appetite vomiting and weight loss in these cats.
What sort of disease?
The reason I say this is that many of these same cats also have a degree of inflammatory bowel disease (IBD) or intestinal cancer. Unfortunately, either of these can be present and there can be no other abnormalities noted on bloodwork, xray or even ultrasound. The only way to confirm the diagnosis is with a biopsy of the intestine.
This can be done via endoscope, but is better performed with an exploratory surgery. The problem with this is that many cat owners are not willing to pursue the diagnosis by these means. It is for that reason that many cats are "suspected" to have IBD or GI cancer as the cause of their symptoms once all of the other easy to find things have been ruled out.
You can discuss with your veterinarian the pros and cons of proceeding with a biopsy to confirm the diagnosis in your pets situation. Even if you choose to not go the route of biopsy, he may benefit from a course of corticosteroids and perhaps a hypoallergenic diet as sometimes food allergies contribute to the IBD. Steroids help many cats with either of the two conditions to regain their appetite and gain weight, but if there is intestinal cancer, the result may be short lived.
What would be a rough estimate on the cost of these tests?
It depends on how the biopsy samples are obtained. Endoscopy is less invasive (no surgery) as so is less expensive, but both require anesthesia. It can run between $500-$1500 ballpark.
If cancer is confirmed with a biopsy, he may do better with other chemotherapeutic drugs to put him in remission for a longer period of time. If the cause is IBD only, you may be able to decrease or even stop the steroids after you see improvement. Biopsy and confirming the diagnosis is always the better choice, but not always feasible for every case. Work with your veterinarian to decide what is best for you and him.
Thanks for your expertise and time.
Here are 2 links you may find informative.
inflammatory bowel disease (IBD)