SYMPTOM
Increased urination
Producing larger volumes of urine or needing to urinate more frequently than established patterns.
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. 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 intact females releases bacterial endotoxins that interfere with antidiuretic hormone activity at the kidney, producing sometimes dramatic increases in urine output. Pyelonephritis can similarly impair renal concentrating ability. Leptospirosis may produce acute kidney injury with associated polyuria during the recovery phase. 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 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 boxes, 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 box 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 boxes, urinate outside the box, 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
Chronic Kidney Disease in Dogs
Diabetes Mellitus in Dogs
Diabetes Mellitus in Cats
Hyperthyroidism in Cats
Cushings Disease in Dogs
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
Increased urination frequently accompanies pyometra due to the effects of bacterial toxins on kidney concentrating ability.
Portosystemic Shunt
Animals with portosystemic shunts typically produce large volumes of dilute urine due to the liver's reduced ability to regulate water balance.
Cats with PKD typically show increased urination as kidneys lose the ability to concentrate urine effectively.
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 toward 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.
When increased urination is accompanied by changes in urine colour — becoming very pale and dilute — rather than the concentrated, darker urine seen with increased frequency from 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 intact female, particularly alongside lethargy, reduced appetite, or vaginal discharge, may suggest a reproductive tract infection that is affecting kidney function through the systemic effects of bacterial toxins.
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 nighttime urination is new, and whether the volume seems proportionally different — helps establish the magnitude of the change. Recording these observations over several days, alongside water intake measurements, creates paired data that is more informative than either measurement in isolation.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS