Sometimes it is obvious that your cat is sick, but most of the time they are very stoic and can hide illness. Here are some things to look for that may indicate illness (or at least a trip to the vet for evaluation)
1. Inappropriate elimination: there are many potential causes of urinating out of the litter box, urinary disease, arthritis, and diabetes to name a few.
2. Changes in interaction: with other pets or humans may indicate disease, fear, anxiety or pain.
3. Changes in activity: decrease in activity is usually associated with arthritis or systemic illness, increases in activity is usually associated with hyperthyroidism.
4. Changes in sleeping habits: sleeping more than "normal" for a cat (16-18 hours a day is considered normal) could be a sign of underlying disease.
5. Changes in food or water consumption: decreased food intake can mean a range of things from poor dental health to cancer, but many cats can be particular about the type or texture of their food; increased food intake can mean potential for diabetes, hyperthyroidism, or other problems.
6. Unexplained weight loss or weight gain: sudden weight loss can indicate hyperthyroidism, diabetes, cancer or several other diseases, whereas obesity can cause an increased risk for joint disease, diabetes, and many other conditions.
7. Changes in grooming: patches of hair loss, excessive matting or changes to your cat's fur is a signal for underlying disease, namely obesity, fear, anxiety, or skin problems.
8. Signs of stress: may be manifested as depression, hide more often, or spend more time awake and observing their environment. If you notice this I would recommend ruling out medical conditions before trying to address behavioral changes as a result of stress.
9. Increases in vocalization: can be seen with hyperthyroidism or increased blood pressure, but could also be because of pain or anxiety.
10. Bad breath: is an early indicator of dental disease, some cats have gum disease as early as 3 years old! When in doubt, have a vet do an oral exam sooner rather than later to prevent extractions and oral surgery.
Hope this helps in assessing your cat and when it is time to come in to the vet!
