Sick Cat Symptoms: When to Call the Vet

Why cats hide illness

In the wild, showing weakness attracts predators and competitors, so cats have evolved to mask signs of pain and disease. A cat with dental pain may still eat, and a cat with kidney disease may drink more without appearing unwell until the disease is advanced. This means that by the time a cat looks obviously sick, the problem may have been developing for days or weeks.

International Cat Care and PDSA both emphasise that subtle changes — sleeping in a different place, grooming less, using the litter tray differently or being less sociable — can be the earliest warning signs. Owners who know their cat's normal routine are best placed to notice these shifts early.

Changes in appetite and thirst

A cat that stops eating is a higher-priority concern than a dog that skips a meal. PDSA advises that cats should not go longer than 24 hours without food because of the risk of hepatic lipidosis, a serious liver condition triggered by fasting. Reduced appetite with no other symptoms can be watched briefly, but a cat that has eaten nothing for a full day needs veterinary advice.

Increased drinking can be just as significant as reduced eating. Cats that consistently drink more water, spend longer at the bowl or seek water from unusual places such as taps or puddles may have polydipsia, which can indicate kidney disease, diabetes or hyperthyroidism. If you notice a sustained increase in drinking, contact your vet.

• Not eating for 24 hours — call your vet, especially if the cat is overweight.
• Eating less but otherwise bright — monitor for 24 hours, then call if no improvement.
• Drinking noticeably more for several days — book a vet appointment.
• Suddenly ravenous but losing weight — contact your vet; hyperthyroidism is a common cause in older cats.

Energy, behaviour and hiding

A cat that is less active than usual, is hiding more, has stopped greeting you or seems withdrawn may be in pain or feeling unwell. These changes are easy to dismiss as mood or weather, but a sustained shift from normal behaviour warrants attention, particularly in older cats.

Sudden aggression, vocalisation at night, restlessness or confusion can also indicate a medical problem rather than a behavioural one. Hyperthyroidism, high blood pressure, arthritis pain and neurological disease can all change behaviour. A short phone call to your vet practice can help you decide whether an examination is needed.

Litter tray and toilet changes

The litter tray is one of the most useful monitoring tools in a cat home. Changes in frequency, volume, effort, colour or smell can signal problems ranging from mild dietary upset to serious urinary or kidney disease. Cats Protection advises checking the tray daily so that changes are noticed promptly.

A male cat that is straining, crying in the tray or passing only drops of urine needs urgent veterinary care because a urinary blockage can be fatal within hours. Diarrhoea with blood, repeated constipation, or a cat that stops using the tray altogether also warrant a prompt call.

• Straining to urinate, especially in male cats — emergency, call now.
• Blood in urine or faeces — contact your vet promptly.
• Diarrhoea lasting more than 24 hours or with vomiting and lethargy — call your vet.
• No stool for more than two days, or painful and unproductive straining — call your vet.
• Urinating much more or much less than usual — book an appointment.

Breathing, eyes, nose and mouth

Normal cats breathe quietly and through the nose. Rapid breathing at rest, open-mouth breathing, noisy breathing or panting are all abnormal and can indicate heart disease, respiratory infection, pain or fluid in the chest. Blue or pale gums signal that the body is not getting enough oxygen and this is an emergency.

Eye or nose discharge, especially with sneezing, can indicate cat flu or other infection. Bad breath, drooling, dropping food or pawing at the mouth can signal dental disease. Red, swollen or squinting eyes should not be left — eye problems can deteriorate quickly.

When to monitor at home safely

A mild, isolated change in an otherwise bright cat — such as eating slightly less for a few hours, being quieter for an evening after a vaccination, or having one slightly soft stool — can often be watched for 12 to 24 hours. Keep the cat comfortable, offer fresh water and familiar food, and note exactly what has changed.

If the change resolves within that window and the cat returns to normal, a vet visit may not be necessary. If it persists, worsens or is joined by another symptom, call your vet. When in doubt, a phone call to the practice costs nothing; UK vet nurses are experienced at triaging and will tell you whether to come in.