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Polyuria and polydipsia (PU/PD) in dogs and cats: differential diagnosis

Polyuria and polydipsia (PU/PD) means a dog or cat is producing more urine and drinking more water than normal, starting either with the kidneys losing water (primary polyuria) or with excess drinking (primary polydipsia).[1,2]

Reviewed by Brian Toncray, DVM · October 22, 2026

Confirming the sign

Owners often describe a pet that empties the water bowl more often or asks to go out overnight, but that history is a starting point, not proof. A measured daily water intake at home and urine specific gravity on more than one sample are what confirm a true polyuric state. Frequent small voids are a different problem: pollakiuria, stranguria and periuria are lower urinary tract signs, and a cat posturing repeatedly in the litter box is more likely to have bladder disease than PU/PD.[3] Once the sign is real, the list below is long because PU/PD can come from disorders of several body systems.[2]

Endocrine differentials

Hyperadrenocorticism (dogs)[4]

Supports it:A middle-aged or older dog whose history and physical examination fit, for example PU/PD with a pot-bellied appearance, panting or symmetric hair loss.

Argues against it:A dog without other consistent clinical signs; the consensus panel advises against endocrine testing unless the picture fits, because no screening test is perfect.

Next test:Chemistry and urinalysis first, then a screening test chosen with the consensus recommendations in mind; abdominal imaging can support the work-up.

Diabetes mellitus[5]

Supports it:Persistent hyperglycemia with glucosuria, weight loss and a good or increased appetite.

Argues against it:A single high glucose in a stressed cat, with no glucosuria; transient hyperglycemia should not be mistaken for diabetes.

Next test:Urinalysis for glucose and ketones, and a fructosamine to show sustained hyperglycemia.

Hyperthyroidism (cats)[6]

Supports it:An older cat with weight loss, a palpable thyroid nodule, restlessness or an unkempt coat.

Argues against it:A total T4 in the reference range in a cat with no compatible signs; early disease can sit in the reference range, so the guideline describes repeat or additional thyroid testing when suspicion stays high.

Next test:Total T4 as the first test.

Hypercalcemia[7]

Supports it:An increased ionized calcium. In dogs, lymphoma was the leading cause in a large series, followed by renal failure, primary hyperparathyroidism and hypoadrenocorticism; anal sac adenocarcinoma also raises calcium.

Argues against it:A normal ionized calcium. Total and corrected calcium did not reliably reflect calcium status in that series.

Next test:Ionized calcium, then a search for the cause: lymph node palpation, a rectal examination of the anal sacs, and imaging.

Renal and urinary differentials

Chronic kidney disease[8]

Supports it:An older cat with azotemia and poorly concentrated urine; CKD is one of the most commonly diagnosed diseases in older cats.

Argues against it:Concentrated urine with no azotemia on repeat testing.

Next test:Chemistry, urine specific gravity, urine protein and blood pressure, repeated over time to stage and monitor the disease.

Pyelonephritis[9]

Supports it:Fever, flank or kidney pain, a positive urine culture, and inflammatory urine sediment in a pet with PU/PD.

Argues against it:A negative urine culture collected before any antimicrobial.

Next test:Urine culture and susceptibility from a cystocentesis sample, with renal imaging.

Reproductive and inflammatory differentials

Pyometra[10]

Supports it:An intact female dog or cat that is unwell, particularly within four months after estrus; vaginal discharge, depression, anorexia, fever, vomiting and PU/PD are typical.

Argues against it:A spayed patient with no remnant ovarian tissue.

Next test:Abdominal imaging of the uterus with a CBC; early diagnosis matters because endotoxemia and sepsis often follow.

Primary polydipsia and vasopressin disorders

Psychogenic polydipsia (dogs)[2]

Supports it:A young, otherwise healthy dog with marked PU/PD, often with a nervous or anxious disposition or compulsive, stereotypical behaviors.

Argues against it:Any abnormal result on routine blood work or urinalysis that points to another cause.

Next test:No single test confirms it; the diagnosis comes from systematically ruling out the other causes on this page.

Central or nephrogenic diabetes insipidus[1]

Supports it:Persistently dilute urine with the common metabolic causes excluded.

Argues against it:Concentrating ability that returns under controlled conditions, which points back toward primary polydipsia.

Next test:A modified water deprivation test or a desmopressin response trial, interpreted with care because partial deficiency or resistance blurs the results.

First diagnostics for this sign

Start with a complete urinalysis that includes urine specific gravity and sediment, a CBC and a chemistry panel, then add a urine culture from a cystocentesis sample.[9] In older cats, add a total T4.[6] If the total calcium is high, measure ionized calcium before chasing a cause.[7] Hold adrenal function testing until the history and examination fit hyperadrenocorticism, because the consensus panel found no screening test good enough to run blind.[4] Water deprivation testing comes last, after everything else is clean, since it carries risk and is hard to interpret.[1]

Example: working the sign

Example. An eight-year-old intact female dog comes in six weeks after her last heat. The owner says she has been drinking far more than usual for several days, is quiet and has stopped finishing meals. On examination she is febrile and has a mucopurulent vulvar discharge. The timing after estrus, the discharge and the systemic signs move pyometra to the front of the list, ahead of the endocrine causes, and the next step is an abdominal ultrasound of the uterus with a CBC rather than an adrenal test.[10] If the uterus were normal, the work-up would return to the urinalysis, chemistry panel and the endocrine differentials above.

Frequently asked questions

Where does the PU/PD work-up start?

A complete urinalysis with urine specific gravity, run alongside a CBC and chemistry panel, with a urine culture from a cystocentesis sample.[9]

Should every dog with PU/PD get a Cushing's test?

No. The ACVIM consensus statement advises running endocrine tests for hyperadrenocorticism only when the history and physical examination are consistent with the disease.[4]

Which causes of PU/PD matter most in an older cat?

Chronic kidney disease, hyperthyroidism and diabetes mellitus belong near the top of the list, which is why an older cat with PU/PD gets a chemistry panel, urinalysis and total T4 early.[8,6,5]

Is psychogenic polydipsia a diagnosis of exclusion?

Yes. No specific test confirms psychogenic polydipsia in dogs, so it is diagnosed after the other causes of PU/PD have been ruled out.[2]

Sources

  1. Paulin MV, Schermerhorn T, Unniappan S, Snead ECR. Arginine vasopressin and copeptin: comparative review and perspective in veterinary medicine. Front Vet Sci. 2025;12:1528008. PMID 40160705 · doi:10.3389/fvets.2025.1528008
  2. Pavlovsky G. Psychogenic polydipsia in dogs - a review of pathogenesis, diagnosis and treatment. J Small Anim Pract. 2026;67(7):580-589. PMID 41688875 · doi:10.1111/jsap.70105
  3. Taylor S, Boysen S, Buffington T, et al. 2025 iCatCare consensus guidelines on the diagnosis and management of lower urinary tract diseases in cats. J Feline Med Surg. 2025;27(2):1098612X241309176. PMID 39935081 · doi:10.1177/1098612X241309176
  4. Behrend EN, Kooistra HS, Nelson R, et al. Diagnosis of spontaneous canine hyperadrenocorticism: 2012 ACVIM consensus statement (small animal). J Vet Intern Med. 2013;27(6):1292-1304. PMID 24112317 · doi:10.1111/jvim.12192
  5. Behrend E, Holford A, Lathan P, et al. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. J Am Anim Hosp Assoc. 2018;54(1):1-21. PMID 29314873 · doi:10.5326/JAAHA-MS-6822
  6. Carney HC, Ward CR, Bailey SJ, et al. 2016 AAFP Guidelines for the Management of Feline Hyperthyroidism. J Feline Med Surg. 2016;18(5):400-416. PMID 27143042 · doi:10.1177/1098612X16643252
  7. Messinger JS, Windham WR, Ward CR. Ionized hypercalcemia in dogs: a retrospective study of 109 cases (1998-2003). J Vet Intern Med. 2009;23(3):514-519. PMID 19658207 · doi:10.1111/j.1939-1676.2009.0288.x
  8. Sparkes AH, Caney S, Chalhoub S, et al. ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease. J Feline Med Surg. 2016;18(3):219-239. PMID 26936494 · doi:10.1177/1098612X16631234
  9. Weese JS, Blondeau J, Boothe D, et al. International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats. Vet J. 2019;247:8-25. PMID 30971357 · doi:10.1016/j.tvjl.2019.02.008
  10. Hagman R. Pyometra in Small Animals. Vet Clin North Am Small Anim Pract. 2018;48(4):639-661. PMID 29933767 · doi:10.1016/j.cvsm.2018.03.001