SYMPTOM
Increased urination
Producing larger volumes of urine or needing to urinate more frequently than the animal's usual pattern.
Renal
As kidney function declines, the ability to concentrate urine diminishes, resulting in the production of larger volumes of more dilute urine. Chronic kidney disease is among the most common causes of polyuria in older cats and dogs. The increased urine output develops gradually as functional nephron mass decreases, and the animal compensates by drinking more to replace the excess water lost through the kidneys. The polyuria in kidney disease tends to be consistent rather than intermittent and progressively worsens as the condition advances.
Endocrine
Multiple hormonal conditions produce increased urination through distinct mechanisms. Diabetes mellitus causes osmotic diuresis when glucose spills into the urine and draws water with it. In dogs, hyperadrenocorticism interferes with the kidney's response to antidiuretic hormone, reducing the ability to concentrate urine. Hyperthyroidism increases renal blood flow and glomerular filtration rate, producing greater urine volumes. Each of these endocrine conditions produces polyuria as part of a broader constellation of metabolic changes.
Hepatic
Liver dysfunction can contribute to polyuria through impaired metabolism of cortisol and other hormones that influence renal water handling, as well as through changes in urea production that affect the kidney's concentrating gradient. Portosystemic shunts, chronic hepatitis, and other hepatic conditions may produce polyuria as one component of a broader clinical picture that may also include altered appetite, gastrointestinal signs, and neurological changes.
Infection
Certain infections can produce polyuria through direct effects on renal function. Pyometra in unneutered bitches releases bacterial endotoxins that interfere with antidiuretic hormone activity at the kidney, producing sometimes dramatic increases in urine output; in cats with pyometra this sign is rare. Pyelonephritis can similarly impair renal concentrating ability. Leptospirosis in dogs commonly presents as acute kidney injury, which can bring increased urination or, in more severe cases, reduced or absent urine output, alongside lethargy, reduced appetite and vomiting. The polyuria in infectious causes may develop relatively acutely compared to the gradual onset of metabolic causes.
Medication-Related
Corticosteroids are the most commonly recognised medication cause of polyuria, producing increased urine output through their effects on renal water handling, often dramatically. Diuretic medications produce polyuria by their intended mechanism of action. Phenobarbital (authorised in the UK for epilepsy in dogs, and used in cats off-licence under the veterinary medicines cascade) and some other anticonvulsants can increase water turnover. Identifying a temporal relationship between starting a medication and the development of polyuria can be straightforward when the association is considered.
Primary Polydipsia
In some cases, increased urination is secondary to increased water intake rather than the reverse. Psychogenic polydipsia, dietary factors such as high-sodium foods, or environmental influences can drive excessive water consumption, with the kidneys appropriately excreting the excess volume. While less common than the medical causes of polyuria, primary polydipsia is typically considered after other causes have been explored, as most animals with polyuria have an identifiable medical driver.
Why timing matters
Early observation
Early increases in urination may be noticed as more frequent requests to go outside, larger wet patches in litter trays, or the occasional need for an additional toilet break during the night. The change may be subtle enough that owners question whether it represents a genuine increase or simply heightened awareness. At this stage, objectively assessing urine output, by noting litter tray weight changes, the frequency of outdoor trips, or the volume of urine produced, can help establish whether a real change has occurred. Early polyuria is often accompanied by proportional increases in water intake, which may itself be the more noticeable change.
Later presentation
As polyuria becomes more pronounced, the practical impacts typically become unmistakable. Dogs may need to urinate much more frequently, including during the night, and may have accidents indoors despite previously reliable house training. Cats may overflow litter trays, urinate outside the tray, or require much more frequent litter changes. The volume of urine per void may increase noticeably, and the urine itself may appear paler and more watery than normal. At this stage, restricting water access, a tempting response to the associated mess, can lead to dehydration, as the increased urine output is typically driven by a physiological process that cannot be safely overridden by limiting intake.
The progression of polyuria generally reflects the trajectory of its underlying cause. Kidney disease produces gradually worsening polyuria over months to years. Endocrine causes may progress at variable rates but tend to worsen as the hormonal imbalance deepens. Infection-related polyuria may develop acutely and resolve with appropriate treatment. Medication-related polyuria typically remains stable while the medication continues. Understanding the rate and pattern of progression (whether sudden, gradual, stepwise, or fluctuating) provides context about the nature of the underlying process.
Conditions commonly associated
Chronic Kidney Disease in Cats
Damaged nephrons in chronic kidney disease lose the ability to concentrate urine, so cats produce larger volumes of dilute urine even as thirst increases to compensate.
Chronic Kidney Disease in Dogs
As nephron function declines, the kidneys lose their ability to concentrate urine, resulting in larger volumes of dilute urine being produced.
Diabetes Mellitus in Dogs
Glucose that spills into the urine once blood sugar exceeds the kidneys' reabsorption threshold draws water with it by osmosis, increasing the volume of urine produced.
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Diabetes Mellitus in Cats
Excess glucose passing into the urine pulls additional water with it, increasing both the volume and frequency of urination.
Hyperthyroidism in Cats
The higher metabolic rate and increased renal blood flow associated with excess thyroid hormone lead to greater urine production.
Cushings Disease in Dogs
Excess cortisol blunts the kidneys' response to antidiuretic hormone, reducing their ability to concentrate urine and resulting in larger volumes being passed.
Urinary Tract Infection in Dogs
UTI causes increased urination frequency (pollakiuria) as bladder wall inflammation reduces the volume at which the urge to void is triggered. Dogs produce small volumes of urine on each occasion and may request to go outside more frequently than usual.
Pyometra
In bitches with pyometra, bacterial endotoxin makes the kidneys less responsive to antidiuretic hormone, and increased thirst and urination are seen in around half of cases; in queens they are rare.
Portosystemic Shunt
Animals with portosystemic shunts can produce large volumes of dilute urine because the liver makes less urea, which weakens the gradient the kidneys use to concentrate urine.
Adrenal Tumours
Excess cortisol from an adrenal tumour reduces the kidneys' ability to concentrate urine, so larger volumes are passed.
Adrenocortical Carcinoma
Excess cortisol production by the tumour reduces urine concentration, increasing the volume passed.
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Cushings Disease in Cats
In cats with Cushing's disease, increased thirst and urination usually come from the diabetes mellitus that develops in most affected cats, rather than from cortisol acting on the kidneys.
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Renal Lymphoma in Cats
As lymphoma disrupts normal kidney function, more dilute urine is produced and passed more often.
Atypical Cushings in Dogs
As in typical Cushing's disease, affected dogs can pass larger volumes of urine more often.
Diabetes Insipidus
When antidiuretic hormone is lacking (central diabetes insipidus) or the kidneys do not respond to it (nephrogenic diabetes insipidus), the kidneys pass unusually large volumes of dilute urine.
Hyperaldosteronism in Cats
Increased thirst and urination can follow the low blood potassium that excess aldosterone causes, or concurrent chronic kidney disease.
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Polycystic Kidney Disease in Cats
As polycystic kidneys lose their concentrating ability, more dilute urine is produced and litter trays need emptying more often.
Steroid Hepatopathy
Excess glucocorticoid, whether from steroid medication or Cushing's disease, causes the liver changes and also reduces the kidneys' ability to concentrate urine, so larger volumes are passed.
Pyelonephritis
Infection in the kidney can impair its ability to concentrate urine and can cause severe, rapid kidney injury, sometimes with lethargy, reduced appetite and vomiting.
Leptospirosis
In dogs, leptospirosis most often presents as acute kidney injury, which can bring increased urination or a fall in urine output alongside lethargy, reduced appetite and vomiting.
Diabetic Ketoacidosis
A life-threatening complication of diabetes mellitus in which increased thirst and urination are followed by vomiting, loss of appetite and lethargy.
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Urethral Obstruction
Frequent attempts to pass urine that produce little or nothing can be mistaken for increased urination; in male cats this can mean a blocked urethra, which can be fatal within two to three days without treatment.
When to explore further
When increased urination is clearly accompanied by increased water consumption, the pairing of polydipsia and polyuria suggests a systemic process affecting water balance rather than a primary bladder or lower urinary tract issue, and this distinction helps direct attention towards metabolic, endocrine, or renal causes.
Polyuria developing alongside weight loss, particularly in an animal that is eating normally or more than usual, may suggest a metabolic or endocrine condition where the body is unable to effectively utilise nutrients despite adequate intake, producing both metabolic wasting and disrupted water balance.
A sudden onset of marked polyuria in a previously normal animal represents a different pattern from the gradual increase typical of chronic conditions, and the acuteness of onset may suggest an infectious, toxic, or acute metabolic trigger rather than a slowly progressive disease. Acute kidney injury from leptospirosis, pyelonephritis or poisons such as antifreeze (ethylene glycol), grapes or raisins, or lilies in cats falls in this group: it is often accompanied by lethargy, vomiting or reduced appetite, can progress to reduced or absent urine output, and can be life-threatening. With antifreeze or lily poisoning the outcome depends on how soon after exposure treatment starts, sometimes within hours, and severity can only be judged with blood and urine tests.
When increased urination produces large volumes of very pale, watery urine, rather than the small, frequent voids seen with lower urinary tract disease, the dilute character of the urine suggests that the kidneys are producing large volumes of poorly concentrated urine.
Polyuria developing in an unneutered female, particularly in the weeks to months after a season and alongside lethargy, reduced appetite, vomiting or vaginal discharge, may suggest pyometra, a uterine infection whose bacterial toxins reduce the kidneys' ability to concentrate urine. Pyometra is potentially life-threatening because sepsis, peritonitis and rupture of the uterus can follow. When the cervix is closed there is often no discharge at all, so its absence does not rule pyometra out, and these animals are often more seriously ill.
In an animal known to have diabetes mellitus, or one with newly increased thirst and urination, the onset of vomiting, refusal of food or marked lethargy can signal diabetic ketoacidosis, a complication whose metabolic disturbances can be profound and life-threatening and cannot be judged at home.
Repeated trips to the litter tray or garden that produce little or no urine, with straining, crying or licking at the genital area, are a different sign from increased urination. In a male cat this pattern can mean the urethra is blocked, a life-threatening problem that can cause kidney failure and death within two to three days without treatment.
Quantifying urine output, while more challenging than measuring water intake, can provide valuable objective data. Noting the frequency of urination, the approximate volume per void, the colour and clarity of the urine, and whether the pattern varies throughout the day or night builds a practical picture. Comparing current patterns against the animal's established baseline (how often it previously needed to urinate, whether night-time urination is new, and whether the volume seems proportionally different) helps establish the magnitude of the change. In an animal that is otherwise bright, eating and passing urine freely, recording these observations over several days, alongside water intake measurements, creates paired data that is more informative than either measurement in isolation.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS