Most pet owners will have been asked by their vet, probably more than once, whether there has been any change in the amount their dog or cat is drinking. It is an important question because the answer can give us valuable information.

Of course thirst increases naturally in hot weather, after exercise and when being fed a dry diet, but it can be much more significant than that. The dog or cat will probably spend more time at the drinking bowl, or the owner will notice that they have to refill it more often than expected. The amount of urine passed will increase as well, and this may be the first sign noticed by the owner.

Common causes of increased thirst in pets

An increase in thirst can be a side effect of certain drugs, but can also be caused by a number of quite serious problems. It is always important to mention it to your vet. Some of the most common causes of increased thirst (polydipsia) are:

1. Fever, which can have many causes including infections or bite wounds

2. Kidney disease, where the kidneys lose their ability to filter waste products from the blood and control its salt content

3. Liver disease, which can take a number of different forms when the various functions of the liver are not being carried out as efficiently as normal

4. Diabetes mellitus, when there is a lack of insulin, a hormone produced by the pancreas which controls blood sugar levels

5. Diabetes insipidus, when the animal lacks anti-diuretic hormones so is unable to concentrate the urine

6. Cushing’s disease, when an excess of natural steroid hormones is produced by the adrenal gland

7. Pyometra (in unspayed females) is an infection of the womb (uterus) which can be sudden or gradual in onset

8. Urinary infection or bladder stones

9. Hyperthyroidism, more common in older cats, where increased thirst is only one of many symptoms caused by an excess of thyroid hormone.

Other causes also occur, and sometimes there is more than one cause present at a time.

Diagnosing the cause

To find out the reason for an increase in thirst, your dog or cat will need to have a full clinical examination. Small clues can be gathered from examination of every part of the body. For example, the colour of the “whites of the eyes” may change in liver disease.

Weight loss or gain could be important. Feeling the abdomen may reveal enlargement of individual organs such as liver or kidneys. A discharge from the vagina could indicate a womb infection (pyometra) in an unspayed female. A heart murmur is often present in hyperthyroidism, and changes in skin and body shape occur in Cushing’s disease.

These clues mean more when considered with the full history of the animal. The age, gender, whether neutered, breed, type of diet, previous illnesses and vaccination status are all relevant. Then the vet will need to ask about the increase in thirst. How long ago did it start? Was it sudden or gradual? Have any changes been noticed in the appetite? You may be asked to measure your dog or cat’s water intake over 24hrs to check whether it is abnormally high or not.

Testing and further procedures

Usually some lab tests will need to be carried out to diagnose the problem. A urine sample is useful to look for signs of infection, crystals or substances which should normally be removed by the kidneys, and to measure the kidney’s ability to concentrate the urine.

A blood test is nearly always needed to distinguish between the various possible causes. The first test is usually a general screening test to narrow it down, followed by more specific tests to reach a diagnosis. To get to the correct diagnosis can take time.

X-rays or ultrasound imaging can be used to visualise the internal organs and might be advised if the results of blood tests suggest they would be useful.

Many of the causes of increased thirst are very serious if left untreated, but many are also very treatable. They require very different treatments, so it is well worth diagnosing the problem so that the right treatment can be given.

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