The high levels of urea seen in CKD cats are released into saliva. An enzyme in the bacteria in the mouth called urease interacts with the urea and produces a very strong and distinctive odour. It is hard to describe the aroma, though once smelled, never forgotten. It is sometimes described as being an ammonia smell (like bleach) but it may smell more like urine (ammonia is a constituent of urine), though neither description really captures the smell. This smell will be particularly noticeable if the cat crashes. If your cat's breath smells more like nail polish remover, this may indicate diabetes.

If the cat is very poorly or in a more advanced stage of renal failure, the toxins produced by the body can cause ulceration of the gums, which occurs when the uraemic waste is converted by the bacteria in the mouth into ammonia (hence the smell of the cat's breath being described as ammonia-like above). You may see ulcers in the cat's mouth if you look inside, or in severe cases your cat may vomit blood (which may also be a sign of bleeding from further down the gastro-intestinal tract). You may also see drooling. Some cats paw at the mouth (which can also be a sign of dental problems).

• a sudden change of food, perhaps to a prescription diet. It is better for a cat's digestive system if a new food is introduced gradually - mix some of the new food with the old and gradually increase the amount of the new food in the mix over a period of several days.

• food intolerance. Because the goal is to reduce protein levels, some CKD prescription foods in particular may have relatively high levels of carbohydrates, and some cats who are used to a higher protein diet may find these harder to process. Introducing the new food gradually may help, but some cats are simply grain-intolerant.

• cats taking antibiotics may develop diarrhoea. The Pet Center discusses this. If you think this might be the cause, contact your vet and ask if you can switch to a different antibiotic. Please do not just stop the antibiotic, however, or the infection may return with a vengeance.

• too much lactulose or MiraLAX, given to treat constipation, may cause the opposite problem of diarrhoea. It is better to start lactulose at a low level and increase as necessary.

• sometimes people think their cat has really runny diarrhoea, but in actual fact, the cat is constipated and the runny liquid is all that can squeeze out round the solid stool. This is known as "overflow incontinence". So do be aware of this possibility, particularly if there is only a small amount of liquid faeces.

• Pet Education and Drs Foster and Smith both mention that potassium supplements may cause diarrhoea.

• nephrotic syndrome, though this is actually relatively rare in cats.

• another disease called Inflammatory Bowel Disease (IBD) may cause diarrhoea. This is covered in Harpsie's website.

• hyperthyroidism may also cause diarrhoea in some cats.

Some CKD cats have a distinctive aroma, which is caused by the levels of toxins in the body. It is similar to the bad breath aroma. You may notice an increase in this aroma or it may develop for the first time if your cat's bloodwork is worsening. In some cases, you may first notice this smell when your cat crashes. Thomas developed this smell seemingly overnight when he crashed, but after treatment it gradually disappeared. 

If allergies are ruled out, this can be a uraemic itch, i.e. caused by the levels of toxins in the blood. If your cat is scratching a lot or grooming excessively, consider this possibility. Itching is fairly common in cats with high phosphorus levels, particularly if the high phosphorus levels go untreated, resulting in secondary hyperparathyroidism. Alternatively itching may indicate a Vitamin B deficiency or be a sign of an essential fatty acids deficiency. Occasionally itching can be a sign of liver problems; if this is the case, your cat's bloodwork should show elevated liver values.

This can be caused by the toxin levels, and if so, it should improve as toxins are controlled. It may also be related to potassium levels, or caused by high phosphorus levels, high blood pressure, calcium imbalances (especially head twitching), hyperthyroidism or Vitamin B deficiency. If your cat only twitches while you are giving fluids, it is probably caused by either the type of fluid used or by giving cold (room temperature) fluids.

Pharaoh's Shakes is a video showing a CKD cat twitching.

Occasionally, if toxin levels are really high (and particularly if a cat is in The Final Hours), a CKD cat may have seizures. In such cases, reducing toxin levels is essential in order to avoid permanent damage to the brain; but this may not be possible if the cat is in his/her final hours.

Seizures may take a number of different forms. There may be the classic jerking and loss of consciousness, but being "spaced out" or mentally absent or staring into space may also be a type of seizure. Harpsie's website has more information on what seizures may look like.

This is sometimes the result of toxin levels in the blood. However, it may also have other causes such as deafness, hyperthyroidism, high blood pressure or occasionally just old age and possibly cognitive dysfunction (senility). 

These problems are so common in CKD cats that there is a page devoted to them. Symptoms covered there include: