Why Is My Cat So Thirsty?

By Leslie Kuczynski, VMD, DACVIM

As  summer has come to an end, it is time for everyone, including our pet family members, to get back to the normal routine. It probably was not surprising with the summer heat, to notice that the water bowls placed around the house needed to be filled more often. With hot weather comes lazy days and cooling off with a refreshing drink. But now that the summer is over, is it normal that your cat is drinking so much water and that the bowls are constantly empty?

Excess thirst, and along with it, excess urination, is a common symptom reported to veterinarians about their pets. Excessive urination, or polyuria, may be noticed more frequently than excessive drinking, or polydipsia, because it can lead to accidents around the house, missing the litter box, or urinating on someone’s favorite shirt, but you can’t have one without the other. Polyuria (PU) and polydipsia (PD) can be the first signs of a long list of disease processes.

So how can you tell if your cat is abnormally thirsty?

The best way for a cat owner to evaluate their cat’s drinking and urinating behaviors is to compare them to what has always been normal for them. There are technical mathematical formulas for how much is too much, but the most important question to ask is: “is she drinking more than she ever did before?” If the answer is yes, then a trip to the veterinarian will help to narrow down the reason why.

So why is my cat so thirsty?

Occasionally the problem starts with excessive drinking. This could be a behavioral problem related to anxiety or stress or a manifestation of an underlying metabolic disease. Most of the time, however, the underlying problem leads to excessive urination and our pets drink more to compensate for all of the water they are losing in their urine. There is a very long list of causes for PU/PD in cats and dogs. This article focuses on three of the most common causes of PU/PD in older cats.

Three of the more common causes of excessive urination and excessive drinking in cats are diabetes mellitus, chronic kidney disease, and hyperthyroidism.

Diabetes mellitus

Diabetes mellitus is a hormonal problem that is diagnosed when blood sugar levels are very high and sugar spills out into the urine. It is caused when either the body is deficient in the hormone, insulin, or when for some reason, the body becomes resistant to its insulin. Insulin is a hormone that is secreted by the pancreas, an organ in the abdomen that is important for secreting hormones that regulate the body’s blood sugar and that digest food. In people, diabetes mellitus is classified into Type 1 (when there is an absolute deficiency in insulin due to autoimmune destruction of part of the pancreas) and Type 2 (when there is insulin resistance or dysfunction of the cells in the pancreas that produce insulin). Diabetes mellitus in cats is more similar to Type 2 diabetes in people. Several factors that predispose people to getting Type 2 diabetes also seem to be important in cats. These factors include obesity, physical inactivity, concurrent diseases, and even genetics. Most cats that develop diabetes mellitus are older than 5 years of age, males are more likely to become diabetic than females, and most are overweight. Signs of diabetes in cats other than increased drinking and urination include increased appetite, weight loss, an abnormal hair coat, or hind limb weakness. Diabetes can be diagnosed by compatible clinical signs and simple blood and urine tests. Treatment involves daily injections of insulin under the skin and routine monitoring by a veterinarian.

Chronic Kidney Disease

Chronic kidney disease is a common ailment of older cats but cats of any age can be affected. It occurs when something is wrong with either the structure or the function of one or both kidneys. The functions of the kidneys include eliminating waste products, balancing electrolytes, producing certain hormones and vitamins, and maintaining the body’s water balance. When the kidneys start to malfunction, urine becomes more dilute and cats start to urinate more. This then causes them to drink more to maintain their hydration. Changes can be found on simple urine and blood tests to indicate kidney disease. Chronic kidney disease is a progressive process and management is based on trying to slow the progression and on treating any symptoms. Symptoms aside from increased thirst and urination can include decreased appetite, weight loss, nausea, vomiting or diarrhea. Treatment involves changes to a kidney-friendly diet, anti-nausea medications and antacids, and specific treatments for concurrent problems like high blood pressure or anemia.

Hyperthyroidism

Hyperthyroidism occurs when the thyroid glands produce excessive active thyroid hormones. Most cats develop hyperthyroidism due to a process called benign hyperplasia (excessive cell growth) in both thyroid glands which are located in the neck next to the trachea or windpipe. Typically, middle-aged to older cats are affected with the average cat being 12 or 13 years old when signs start. Thyroid hormones are important for many basic metabolic functions in the body. They are important for regulation of heat and metabolism of nutrients (carbohydrates, proteins, and fats). Excess thyroid hormones increase metabolism and can lead to weight loss. They can also increase heart rate and blood pressure and can make the heart work faster causing damage to the heart muscle. Signs usually include increased appetite, weight loss, hyperactivity or restlessness, cold-seeking behaviors, and vomiting or diarrhea. Hyperthyroidism can be diagnosed with simple blood tests. Treatment involves oral medications or radioactive iodine treatment at a specialty hospital.

So how can I find out why my cat is so thirsty?

The first steps in determining the underlying cause of PU/PD is a complete physical exam of your cat, a thorough history, and laboratory work at your veterinarian’s office. The exam is important to thoroughly evaluate your cat for signs of common problems associated with PU/PD (see discussion above). The history is important to ensure that the problem is truly too much urinating and drinking and not other symptoms that can sometimes seem similar. For example, a cat that has a urinary tract infection might seem to be urinating a lot, but the urine volume is actually normal, and she just feels like she has to urinate more because of the infection, so she goes in and out of the litter box many times in a day. This is not true polyuria or increased urination, but it is increased frequency of urination, which is also known as pollakiuria. Urinary incontinence can also be mistaken for urinating too much, but has its own list of underlying causes which are not discussed here.

Laboratory testing that will help determine the underlying cause of your cat’s include a complete blood count (or CBC), a biochemical screen, a urinalysis, and a urine culture. The CBC will look for signs of infection or inflammation in the blood, the biochemical screen will evaluate many different values that are specific to different organs and their functions such as the liver, the kidneys, the gastrointestinal tract, and it will also look at electrolytes like sodium and potassium. One of the most important pieces of the laboratory puzzle will be the urinalysis and the urine culture. The urinalysis will look at you cat’s kidney’s ability to concentrate the urine and also will look for signs of infection. Many of the underlying causes of PU/PD can predispose cats to developing urinary tract infections, so the urine culture, which is a test to grow any bacteria that is present and identify it, is very important in all animals exhibiting these symptoms.

In summary, if you have noticed that your cat seems to be drinking more water than usual even now that the weather has cooled down, or if it seems like there is more urine in the litter box or like she is using the litter box more often, schedule a visit with your veterinarian. With your veterinarian’s help and some simple laboratory tests, an underlying reason may be discovered. Your veterinarian can then advise you on any additional tests that might need to be performed and on specific treatment recommendations that are right for you and your cat.