CONDITION
Acute Kidney Injury
Acute kidney injury describes a situation in which the kidneys suddenly lose much of their ability to filter waste from the blood. This can happen over hours or days, rather than the slow decline seen in chronic kidney disease. The kidneys may recover function if the underlying cause is identified and addressed, though the degree of recovery varies. Owners often notice a sudden change in how much their pet is drinking or urinating—sometimes much more than usual, sometimes very little. Appetite may drop sharply, and vomiting or listlessness can appear within a short window. The change tends to be abrupt enough that many owners can identify when things shifted. This page explores what signs may appear in the early stages, what mechanisms inside the kidney can lead to this kind of injury, how the condition is investigated through blood tests and imaging, and what approaches exist depending on the cause and severity. The focus is on understanding what acute kidney injury looks like and how it tends to unfold.
Why this matters now
Acute kidney injury can appear at any age, though the triggers often differ by life stage. Younger animals may encounter toxins—certain plants, antifreeze, or medications given without veterinary guidance—while older pets are more vulnerable to complications from infections, dehydration during illness, or reduced blood flow during anaesthesia or surgery. Some breeds carry a slightly higher risk of conditions that predispose to kidney injury, but environmental and circumstantial factors tend to play a larger role than genetics in most cases.
The decline in kidney function typically unfolds over hours to a few days, rather than weeks or months. In some cases, the kidneys begin to recover within days if the inciting cause is removed and supportive care is provided, though the timeline and degree of recovery vary widely between individuals. A smaller proportion of animals do not regain full function and may transition toward chronic kidney disease, while others recover nearly completely. The first 48 to 72 hours often give the clearest indication of how the injury is evolving.
Signals & patterns
Early signals
Sudden change in drinking
Some animals begin drinking noticeably more water than usual, while others may drink very little or stop entirely. The shift tends to happen over a day or two, and many owners can recall when the pattern changed.
Altered urination volume
The litter tray may become unusually wet, or a dog may ask to go outside more frequently and produce larger puddles. In other cases, urination may drop off sharply or cease, which can be harder to notice if the pet toilets outdoors.
Loss of appetite
Food that was reliably eaten may be ignored or only sniffed. The drop in interest often appears suddenly rather than fading gradually, and may coincide with other changes in behaviour.
Vomiting or nausea
Repeated vomiting, sometimes with nothing in the stomach, or signs of queasiness such as lip-licking, drooling, or reluctance to move can appear early. The pattern may worsen over hours.
Quietness or withdrawal
A normally sociable pet may seek out quiet corners, sleep more than usual, or show less interest in greetings or play. The change in demeanour often accompanies the other physical signs.
Later signals
Weakness or unsteadiness
As waste products accumulate in the blood, some animals become visibly weak, wobbly on their feet, or reluctant to stand. This tends to develop over days rather than hours.
Mouth ulcers or bad breath
A sharp, chemical smell on the breath or small raw patches inside the mouth can appear when kidney function is severely impaired. These signs reflect rising levels of waste compounds.
Seizures or confusion
In more advanced cases, toxins that the kidneys can no longer clear may affect the brain, leading to disorientation, trembling, or seizures. This is less common but represents a severe stage.
Click to read about the biological mechanisms
How this is usually investigated
Investigation typically begins with a detailed history of recent events—any changes in drinking, urination, appetite, or exposure to toxins—followed by physical examination. Blood and urine tests help establish whether the kidneys are failing to filter waste and whether other organs are affected. Imaging and additional tests may follow if the initial picture is unclear or if a specific underlying cause needs confirmation.
Blood biochemistry
Urinalysis
Physical examination
Abdominal ultrasonography
Urine culture
Options & trade-offs
Management is usually built from a combination of approaches tailored to the suspected cause, the severity of the injury, and what is practical for the household. Some animals are managed at home with close monitoring, while others need hospital-based support. Different owners and animals find different combinations workable, and the plan often shifts as the kidneys respond—or fail to respond—over the first few days.
Intravenous fluid therapy
Fluids are administered through a vein to restore hydration, support blood flow to the kidneys, and encourage urine production. The rate and composition of the fluids are adjusted based on electrolyte levels and urine output. This approach is often continued for several days while blood tests are repeated to track kidney function.
Trade-offs: Requires hospitalisation with intravenous access, which can be stressful for some animals and costly for owners. Fluid overload can occur if the kidneys are not producing urine, leading to fluid accumulation in the lungs or abdomen.
Identifying and removing the inciting cause
If a toxin, medication, or infection is suspected, efforts focus on stopping further exposure or treating the underlying trigger. This may involve discontinuing a drug, administering antibiotics for a bacterial infection, or providing specific antidotes where available. Addressing the cause early can limit the extent of permanent damage.
Trade-offs: The inciting cause is not always identifiable, and some toxins have no specific antidote. Even when the cause is removed promptly, the kidneys may have already sustained injury that takes weeks to heal or may not heal completely.
Nutritional support
Feeding may involve hand-feeding, appetite stimulants, or temporary feeding tubes if the animal is not eating. Diets lower in protein and phosphorus are sometimes introduced to reduce the workload on the kidneys, though this depends on the animal's overall condition and whether nausea is limiting intake.
Trade-offs: Many animals with acute kidney injury have nausea or vomiting that makes eating difficult, and forcing food can worsen distress. Feeding tubes require sedation or anaesthesia to place and need daily maintenance, which some households find difficult to manage.
Medications to manage complications
Drugs may be used to control nausea, reduce stomach acid, lower blood pressure, or correct electrolyte imbalances such as high potassium. Each medication targets a specific secondary problem rather than the kidney injury itself. The combination used varies depending on which complications arise in a given animal.
Trade-offs: Some medications require precise dosing and monitoring to avoid side effects, and not all complications respond reliably to drugs. The cost and frequency of administration can accumulate if multiple drugs are needed over several weeks.
Haemodialysis or peritoneal dialysis
Dialysis mechanically filters waste products from the blood when the kidneys cannot do so. Haemodialysis uses an external machine and is available only at a small number of specialist centres, while peritoneal dialysis uses the abdominal lining as a filter and can sometimes be performed in a general referral hospital. These techniques can sustain life while the kidneys are given time to recover.
Trade-offs: Dialysis is expensive, requires specialist expertise, and may involve multiple sessions over days or weeks. It is not available in all regions, and not all animals tolerate the procedures or the confinement they require. Dialysis supports the animal but does not repair the kidneys, so recovery still depends on the underlying injury healing.
Common misconceptions
"If the kidneys have been injured, they will never work properly again."
Acute kidney injury differs from chronic kidney disease in that the kidneys often retain some capacity to repair themselves if the inciting cause is brief and supportive care is provided early. Some animals regain nearly full function, though others are left with partial impairment that may progress over time. The first few days of monitoring tend to clarify which trajectory an individual is following.
"Normal urine output means the kidneys are recovering."
Urine production can increase even when kidney function remains poor, because the remaining nephrons may produce dilute urine without effectively clearing waste. Blood tests that track creatinine and electrolytes give a more reliable picture of whether filtration is improving. Volume alone does not confirm recovery.
"Acute kidney injury only happens to old animals."
While older pets may be more vulnerable to certain triggers such as reduced blood flow during surgery or infection, younger animals can develop acute kidney injury from toxin exposure, trauma, or infections such as leptospirosis. Age influences the range of likely causes but does not protect against the condition.
Related conditions
Chronic Kidney Disease in Dogs
Chronic kidney disease describes a gradual decline in kidney function over months or years, whilst acute kidney injury involves a sudden loss of filtration capacity over hours or days. In some cases, an episode of acute injury can leave residual damage that becomes the starting point for chronic decline, and animals with pre-existing chronic disease may be more vulnerable to acute decompensation when faced with dehydration, infection, or other metabolic stress.
Chronic Kidney Disease in Cats
Chronic kidney disease in cats develops slowly over time, whereas acute kidney injury describes a rapid loss of kidney function. Cats with long-standing chronic disease can experience acute deterioration triggered by dehydration, infection, or other metabolic challenges, and acute injury that does not fully resolve may transition into a chronic pattern of reduced filtration capacity.
Systemic Hypertension in Cats
Systemic hypertension in cats often arises as a consequence of chronic kidney disease, and persistently elevated blood pressure can in turn damage the small vessels inside the kidney. In the context of acute kidney injury, high blood pressure may develop rapidly as part of the body's response to impaired kidney function, or pre-existing hypertension may contribute to the severity of the injury itself.
Acute Pancreatitis
Acute pancreatitis and acute kidney injury can occur together, particularly when systemic inflammation or reduced blood flow affects multiple organs at once. Severe pancreatitis may lead to dehydration, changes in blood pressure, or release of inflammatory mediators that can reduce kidney perfusion, whilst kidney injury can complicate the metabolic picture in an animal already struggling with pancreatic inflammation.
Urinary Tract Infection in Dogs
Urinary tract infections in dogs typically affect the bladder or urethra, but in some cases infection can ascend to the kidneys themselves—a process known as pyelonephritis—which may trigger acute kidney injury. Conversely, acute kidney injury from other causes can alter the normal environment of the urinary tract, sometimes increasing susceptibility to secondary infection.
Understanding how acute kidney injury unfolds can open questions about related conditions that affect the urinary system, such as urinary obstruction or chronic kidney disease, and how these differ in their patterns and timelines. The broader context of metabolic health explores how the kidneys interact with other organs in maintaining fluid balance, electrolyte levels, and waste clearance. Observations made at home—changes in drinking, urination, or energy—often form a useful foundation for conversations that help clarify what may be shifting and what monitoring may be helpful over the weeks ahead.
Last reviewed: 30 June 2026 · Dr Alastair Greenway MRCVS