PU/PD Series: Acute and Chronic Renal Insufficiency

The nephron, the functional unit of the kidney, can be damaged in many ways to cause renal insufficiency.

Along with all the other organs that can cause PU/PD (increased urination and drinking known as polyuria/polydipsia), the kidneys themselves are sometimes to blame. While renal disease is complex, it is important to understand some acute and chronic kidney problems that lead to PU/PD.

With acute or chronic insults to the kidneys, the ability of the kidneys to concentrate urine is lost; in most cases, the renal tubules that are responsible for drawing water back out of the urine, are damaged. The pet urinates out a higher percentage of water, thus diluting the urine and leading to possible dehydration. The pet drinks more water to counter this loss, and is officially PU/PD.

PU/PD: What It is and What Causes It

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?