It’s winter. Heat’s on, wood stove stoked. It’s dry inside. Everyone drinks more water, including the dogs, so I’m not always concerned when clients mention their pups are drinking more water this time of year. I ask about other symptoms, do a complete physical examination, then, if indicated, suggest laboratory tests. When should we worry if Spongebob, the Spaniel, is draining his water bowl?
Technically called polydipsia (PD), increased thirst often pairs with polyuria (PU), production of excessive amounts of dilute urine. PU/PD is a chicken-egg situation. Which comes first? Is Spongebob drinking more, thus creating more urine, like humans after a few too many beers? Or is he peeing excessively because something is wrong with his ability to concentrate his urine, causing excessive fluid loss, for which he compensates by drinking more?
Owners’ perceptions are not always accurate, so it is good to confirm polydipsia by scientifically measuring water consumption. Here’s how. Empty his water bowl. Measure and refill with more water than he could possibly consume in one day. Note time and amount. Now have a nice quiet day. Don’t feed anything unusual, salty, or sweet. No beach walks or extra exercise. Just hang out. Prevent access to other water sources, like puddles or toilets. Twenty-four hours later, measure the water left in the bowl, then subtract this from the starting quantity. Voila! There’s his 24-hour water consumption.
Is it abnormal? Normal is less than 100 milliliters per kilogram body weight per day. Say Spongebob drank 10 cups. One cup equals 237 milliliters, so he drank 2,370 mls. How much does he weigh? In kilograms. (C’mon, folks. Go metric.) Make it easy. Say he weighs 44 pounds. That’s 22 kilos. Now do the math. Or call your veterinarian and we will do the math — amount consumed (in milliliters) in one day divided by body weight (in kilograms). Spongebob’s comes to 108 mls/kg BW/day. That’s polydipsia.
Urinalysis is also essential. The specific gravity tells us the urine concentration. Dipstick measures pH, and whether there are protein, glucose, blood, or ketones present. Microscopic sediment examination can reveal red and/or white blood cells, crystals, casts, epithelial cells — things that may point us toward infection, inflammation, even cancer. It’s also helpful to know how much urine Spongebob produces daily, but few owners are willing or able to collect and measure this, so quantifying urine production is usually reserved for hospitalized patients. What owners can notice is increased frequency and/or urgency, and incontinence, i.e., leaking urine involuntarily when lying down or sleeping.
Common causes of PU/PD in dogs include kidney disease, diabetes mellitus, and an adrenal gland disorder commonly known as Cushing’s disease. Kidney disease can be caused by infection, toxins, cancer, immune disorders, age-related degeneration, and more. Other less common causes of PU/PD include liver or thyroid disease, and diabetes insipidus, a disorder affecting production or release of antidiuretic hormone. All this can get complicated. No single test gives all the answers.
Doctors have a saying, “If you hear hoofbeats, don’t look for zebras.” In other words, start by looking for the common things. If Spongebob is elderly, kidney failure. If Spongebob is an obese middle-aged dog eating ravenously but losing weight, diabetes mellitus. If urinalysis suggests infection, do bacterial cultures on a sterilely collected specimen. Elevated liver enzymes? Evaluate adrenal gland and liver function. See? Complicated.
This winter I have seen several dogs with various combinations of excessive drinking and/or urination. The first, a 12-year-old spayed female, had a previous history of urinary tract infections. She was drinking excessively and urinating everywhere. We ruled out diabetes, kidney failure, and Cushing’s disease. I advised urine culture, but her owner asked to try treating empirically with antibiotics before doing more diagnostics. Although unnecessary antibiotic use contributes to antibiotic-resistance globally, in this case empirical antibiotic treatment seemed reasonable, considering her previous history of infections. Urinary tract infection that goes to the kidneys, called pyelonephritis, can cause PU/PD. Sure enough, within days of starting antibiotics, the PU/PD resolved.
The next dog was elderly. Water consumption measurement confirmed polydipsia. His urine was excessively dilute. We ruled out kidney failure and diabetes, but were suspicious of Cushing’s and/or liver disease. Additional tests for Cushing’s were equivocal, neither confirming nor ruling out adrenal gland problems. We prescribed medication to support liver function, with plans to retest in a month, but by then, the excessive drinking had stopped. During this time, his owner had changed his diet. Perhaps his previous food was too salty? Perhaps the liver medication helped? Impossible to know. For now, everything seems back to normal. A mystery we will continue to monitor.
The third dog, only six months old, was recently adopted from a rescue organization. Her new family immediately noticed her guzzling lots of water, urinating frequently, and having trouble housebreaking. “Could be behavioral,” I said. Dogs from rescue situations may not have had free access to water, so may drink excessively when first adopted, and have delayed house training if previously allowed to urinate in their kennels. We did standard diagnostics. Her liver enzymes were slightly elevated, so we ran bile acids test, ruling out a congenital condition called portosystemic shunt. We now plan to sterilely collect urine for culture.
Because she is so young, I’m also thinking about zebras instead of horses. Might this be a complication from her spay, such as an occluded ureter? Diagnosis would need radiographs, maybe ultrasound. Another zebra is diabetes insipidus — lack of antidiuretic hormone. In the old days, we used to do “water deprivation testing” to make this diagnosis, slowly depriving a patient of water to see if their body responded appropriately, but sometimes this test led to severe dehydration, collapse, even kidney failure. A safer test is a therapeutic trial of medication called DDAVP, which replaces the missing hormone. We just take one step at a time, as we try to solve each case of PU/PD. But it’s complicated. See?