It could be so many things, Jon. You are doing the right thing by trying to eliminate obvious potential causes but there are many cat diseases that don't show up on an ordinary blood panel such as IBD and pancreatitis.IBD is usually diagnosed via symptoms as there is no real test - took mine to the Royal Vet College and they confirmed it was by far the most likely cause of her vomiting and diarrhoea. She is on an extremely strict diet which helps a lot. Pancreatitis is diagnosed through a specialist blood test, not part of the normal blood test panel. I have had cats with both (as abpve still currently have one that had IBD from when I brought her home as a kitten) and those can cause frequent vomiting. But food allergies can also play a part, maybe try some grain and veg free food as well, not easy to find but I can give you some brand names that have worked for mine. Also, have you changed their food recently? All mine have vomited after eating IAMS.
Claire Moran ● 2005d