How to tell if a cat is sick

Cats do slow down as they get older so don't worry too much. 

Keep an eye on them though for a change in behaviour maybe a spike in energy as this can indicate pain. 

It doesn't hurt to have a vet check just to see if everything is OK. 

Hi Harry,

Firstly I would like to say that as a member of the veterinary world we would always prefer for an owner to bring their fur children into clinic or ask for a phone consultation with any concerns as we have dedicated our careers to helping animals regardless of the issue! So please don't feel bad or embarrassed with a 'small' concern. At the end of the day you care and love your cat and we appreciate how much they mean to us as individuals. 
 

You definitely can check your cats vitals. If you raise their lip and expose their gums  you can look at the mucus membranes and capillary refill time. Ideally (and each cat is different/ may have pigment on the gums) their gums will be a nice pink colour, not too pale and not bright or dark red. If they are one of the extremes then a trip to the vet won't hurt. If you press the gun lightly and count in your head the time it takes to return to the normal colour, it should roughly be < 2 seconds. 
Observe your cat from a subtle distance and count their respiration rates whilst they rest for 15 seconds, stick to either inhalation or expulsion to reduce confusion whilst counting, doing so from a distance won't affect their resp rate whereas getting close may excite them, causing them to breathe faster etc. Once you've done this x the answer by 4 to get an average for a minute - a healthy range is between 16 and 40bpm.

For heart rate can use their pulses, feeling on the left side, behind their front leg or behind their main pad on a hind foot. Count again for 15 seconds and x4. A healthy range would be between 160 and 180. 
Finally you could buy a thermometer but be warned, dress up like you're expecting heavy snow to avoid the scratches! Pop it in her bottom and 100.5°F and 102.5°F (38.1°C and 39.2°C) would be considered normal.

Sadly with age passing on is natural so here are a few signs to look out for:

• Lack of Interest In Eating and Drinking. It's common for cats to lose their appetite toward the end of their lives.
• Extreme Weakness. You will notice your cat becoming more lethargic and refusing to move.
• Lower Body Temperature.
• Changes in Appearance and Smell.
• Seeking Solitude.