The studies used to establish the “normal” ranges for BUN (blood urea nitrogen) in cats are based on cats that were not fed species-appropriate high-meat-protein diets. A cat on a healthy, high-meat-protein diet will often have levels that are somewhat higher – i.e, outside the so called “normal” range of laboratory results.
So what? If your cat’s blood work comes back with a higher than “normal” BUN – and your cat is on a raw meat-based diet – make sure your vet accounts for this in using BUN as a definitive diagnostic marker for determining if your cat has kidney disease. Dr. Elizabeth Hodgkins notes, “[Veterinarians] need to be aware that some degree of elevation is normal in such patients and is not harmful.”
As the Feline Nutrition Foundation puts it:
Raw-fed animals have a complete range of highly digestible, animal-based amino acids available to them, so it is not unexpected that more BUN is produced. Human BUN also increases on a high-protein diet.