At vet school you have to learn 17 different reasons for a dog or cat to be excessively thirsty: from nerves (my old dog used to down a full bowl after a squabble with his friend), all the way to sepsis and kidney failure.
Other than because it’s a boiling hot Portuguese summer, there are a few common reasons in cats, which we’ll look at today.
Diagnosing the source of your cat’s drinking problem (sorry, bad pun) can be as simple as looking at their diet; the addition of salty snacks will make anyone thirsty. Similarly, many dry food brands in the supermarkets are popular due to price and TV coverage. To keep the price right, most of these brands add loads of salt to increase tastiness, masking the quality of the ingredients. In the young, otherwise well cat, who has not been exposed to kidney-damaging plants like lilies, dietary change may turn out to be a really easy answer.
Most of the thirsty cats are at least middle-aged and may have more than 1 condition, making diagnosis and management more complicated.
A urine sample can be illuminating. Normal cat wee should be strong (the kidneys hold onto most of the fluid in the body, only letting out the excess), with no protein nor sugar (both kept inside the body by the kidneys). A diabetic cat will have sugar (glucose) in his/her wee, reflecting high blood sugar, and usually be super-thirsty. Feline diabetes is most similar to human type-2 “late-onset” diabetes. And, like humans, the cats tend to be plump. Unfortunately, unlike type-2 humans, most diabetic cats are not manageable by diet and tablets; they need daily insulin injections. The diabetic cat will initially seem quite happy – hungry, thirsty, weeing a lot, but well. Without treatment, after a while, they become thin, start to feel ill, and eventually develop diabetic ketoacidosis (total metabolic derangement, where the cat poisons itself trying to manage the high sugar levels in its body). A cat in this condition will look very poor indeed and require a stay in the intensive care unit if it is to have a hope.
The thyroid gland (in the neck) governs your cat’s metabolism. If the gland becomes overactive (common in older kitties), the metabolic rate goes up, causing a fast heart rate and a cat that needs to eat a lot, while getting thinner and thinner. For some cats the urge to guzzle everything in sight extends to water. These cats will have normal urine. Diagnosis is via a blood test, and management is usually tablets. There are other treatments which can be curative, including surgery and (depending on region) radioactive iodine therapy.
Chronic kidney disease is probably the most infamous condition of thirsty cats. As kidney function deteriorates, water that would normally be held in the body is lost into the urine. The cat drinks more, to compensate. Similarly, protein is lost too, leading to weight loss. Eventually, urea and creatinine (waste products from protein digestion) start to build in the bloodstream instead of being excreted via the kidney, making the cat feel ill. Urine dilution and the presence of protein occur before blood chemical levels start to climb – 67% of kidney function has to be lost for changes in urea and creatinine to show on a blood test, and 75% before the cat feels poorly. As the chemical levels get more skewiff, other blood changes happen – bones start to leach phosphorus, causing nausea. Potassium levels can plummet, resulting in general weakness and poor appetite. Thirst eventually becomes unslakeable. Dietary modification, tablets to support kidney function, and supplements to modify phosphorus and potassium are often very successful at helping these cats achieve decent quality (and quantity) of life.
These days, there is so much that can be done – please don’t leave your beloved cat too long before getting him/her checked out – it can make a huge difference to the outcome.