Owners notice when they need to fill the water bowl more than usual

If you look at the daily schedule in a vet’s treatment room, you might see something like this next to the patient name: “K9: √ ears” (check for infection/irritation in this dog’s ears), “lag: ADR” (the owner of this bunny thinks it “ain’t doin’ right”), or “fel: Ⓥ” (this cat has been vomiting). These are all very useful shorthand notations that allow the vet to start thinking about how to approach the case before she enters the exam room.

Another very useful abbreviation is “PU/PD.” This is shorthand for a medical term: polyuria and polydipsia, which simply means urinating and drinking more than normal. There are many possible causes of PU/PD in cats and dogs; so it’s important to make a mental rule-out list that’s consistent with species, age, and other owner complaints, like vomiting or weight loss. The important thing here is to start with the “horses” (as in, “when you hear hoof beats, think horses [common diseases], not zebras [rare diseases]”). So, what are the PU/PD “horses” for cats and dogs and how do you diagnose them?

The most common causes of PU/PD in our companion animals are:

  • hyperthyroidism (cats)
  • diabetes mellitus
  • acute or chronic renal insufficiency
  • lower urinary tract disease (like bladder infections)
  • hypercalcemia (often secondary to feline lymphoma)
  • uterine infection (pyometra)
  • liver disease
  • Cushing’s Syndrome (dogs)

To diagnose or rule out these possible causes, we need a good history, physical exam, basic blood work, and urinalysis. Based on the results of these, radiographs, special challenge tests, and ultrasound might be warranted.

History: The owner can tell us how the problem started. Was it very sudden or gradual (acute versus chronic disease)? Is there difficulty with urination, like straining, or passing blood (lower urinary tract disease)? Is the pet eating the same amount but losing weight (hyperthyroidism)? Has there been increased activity level (hyperthyroidism)? Has there been vomiting (renal insufficiency, liver disease)? Has the pet been taking steroids (like prednisone), which are known to cause PU/PD?

Physical exam: The important findings for a physical exam on a PU/PD animal are body condition (weight loss in hyperthyroidism/diabetes/lymphoma/renal disease or pot-bellied appearance with Cushing’s), coat condition, breath odor (renal disease can lead to foul breath), heart rate (often elevated in hyperthyroidism or with infection like pyometra), mucus membrane color (can be yellowish with liver disease), body temperature (often elevated with infections), and unusual organ size or texture during palpation (pyometra, liver disease, lymphoma, kidney disease).

Diagnostics: The “minimum database” of blood work and urinalysis are often all that’s needed to diagnose the cause of PU/PD. The levels kidney markers, liver markers, thyroid hormone, and blood glucose can almost immediately rule in or out renal disease, liver disease, hyperthyroidism, and diabetes mellitus. And urinalysis can usually rule in/out a lower urinary tract infection.

Advanced tests:  Because it usually allows good visualization of target organs, ultrasound can be great for diagnosing – or assessing the degree of damage from – pyometra, lymphoma, Cushing’s, kidney or bladder disease, and many liver diseases. Clinics that do not have ultrasound can use x-rays to visualize some organs; but the detail is not typically as good as with ultrasound. Cushing’s has markers on blood work, but is usually ruled in/out with a low dose dexamethasone suppression test that measures adrenal function.

Treatment: Treatment is based on actual diagnosis. In many cases the PU/PD will resolve with treatment and its recurrence may be used as a marker that treatment needs to be evaluated. In cases of renal disease, however, PU/PD is usually a permanent state and ample water should always be available for these pets.

Owners are pretty aware of how often they need to fill a water dish, scoop litter, or let their dog out to urinate. So, it’s no surprise that PU/PD is often an owner’s first clue that a pet is having health problems. And, because it’s caused by so many and varied illnesses, there’s no surprise that PU/PD is a frequent trigger for a vet to start thinking about those “horses.”

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