Acute Kidney Injury in Cats: Causes, Signs & Treatment

Last reviewed April 2026 · Veterinary reference article

AKI vs. Chronic Kidney Disease: Why the Distinction Matters

Both AKI and chronic kidney disease (CKD) cause elevated creatinine and BUN on bloodwork — but they are fundamentally different conditions with very different causes, timelines, and treatment approaches.

The distinction also matters because AKI can happen on top of existing CKD — called "acute-on-chronic" kidney disease. A CKD cat with a dehydrating illness, a urinary obstruction, or an NSAID dose can tip into AKI. These cats are at higher risk because their kidney reserve is already depleted.

Causes of AKI in Cats

Toxins

Lily toxicity works by direct tubular toxicity — the nephrotoxic compound (not yet fully characterized) destroys the cells lining the kidney tubules. Clinical signs begin within 6–12 hours of ingestion: vomiting, drooling, lethargy. Within 24–72 hours, acute kidney failure sets in. Treatment before kidney damage is established (aggressive IV fluids within 18 hours of ingestion, decontamination if very recent) can be lifesaving. After kidney damage is established, prognosis is guarded to poor.

Ethylene glycol (antifreeze) is acutely toxic in very small quantities — less than 1.5 mL/kg is a lethal dose in cats. Ethylene glycol is metabolized to oxalic acid, which precipitates in kidney tubules as calcium oxalate crystals, causing complete tubular destruction. Treatment with fomepizole (4-MP) or ethanol must begin within hours of ingestion — the window is extremely narrow and prognosis after 6 hours is very poor. Signs include ataxia (drunken gait), vomiting, then apparent recovery followed by acute kidney failure 24–72 hours later.

NSAIDs — including meloxicam (Metacam), ibuprofen, and naproxen — reduce prostaglandin-mediated blood flow to the kidneys. In healthy cats with good blood pressure and hydration, a single appropriate dose is unlikely to cause harm. But in cats that are dehydrated, hypotensive, anesthetized, or have underlying CKD, NSAIDs can precipitate AKI. Human NSAIDs (ibuprofen, naproxen) are especially dangerous — never give without explicit veterinary instruction.

Urinary Obstruction

A urinary obstruction (blocked bladder — most common in male cats with FLUTD or urethral plugs) prevents urine outflow and causes back-pressure that rapidly damages kidney tissue. The longer the obstruction, the more severe the AKI. A cat that has been blocked for 24–48 hours can develop severe, potentially irreversible kidney injury in addition to life-threatening electrolyte disturbances (hyperkalemia causing cardiac arrhythmias). This is why a blocked cat is always a veterinary emergency.

Reduced Blood Flow to the Kidneys (Pre-Renal AKI)

When blood pressure falls or blood volume drops, the kidneys receive inadequate perfusion and begin to shut down. Causes include severe dehydration (from gastroenteritis, prolonged anorexia, or other illness), hemorrhage, heart failure, and hypotension under anesthesia. This form of AKI is often reversible with IV fluid resuscitation if caught early — the kidneys themselves are not initially damaged, just underperfused. Prolonged underperfusion, however, leads to ischemic kidney damage that may not fully reverse.

Infectious Causes

Pyelonephritis (bacterial kidney infection) can cause AKI when infection is severe, bilateral, or when there is pre-existing CKD. Feline infectious peritonitis (FIP) can also affect the kidneys. Leptospirosis — while more commonly associated with dogs — has been reported in cats and can cause acute kidney injury.

Symptoms of AKI in Cats

AKI symptoms reflect both the kidney failure itself and the accumulation of uremic toxins (waste products normally cleared by the kidneys). The onset is dramatic compared to CKD — an owner may describe a cat that was completely normal 12–24 hours ago:

• Profound, sudden lethargy — often described as collapse or extreme weakness
• Vomiting — may be persistent and severe
• Complete anorexia — sudden and total loss of interest in food
• Decreased or absent urination (oliguria/anuria) — cat may not visit the litter box, or produce only small amounts
• Uremic halitosis — ammonia or chemical smell on the breath from accumulating toxins
• Oral ulcers or drooling — from uremic toxin irritation of the mouth lining
• Dehydration — dry, tacky gums; skin tenting
• Hypothermia — subnormal body temperature in severe cases
• Pain on kidney palpation — kidneys may be swollen and tender

In some cases — particularly early pre-renal AKI or early post-obstructive — cats may paradoxically increase urination as the kidneys attempt to compensate. This can be misleading; increased thirst and urination alongside sudden lethargy and vomiting still warrants urgent evaluation.

Bloodwork in AKI: What to Expect

The defining feature of AKI on bloodwork is a rapid rise in kidney values. Context matters enormously — a mildly elevated creatinine in a cat with a two-year history of CKD is very different from the same value in a cat that was normal 48 hours ago.

Urinalysis Findings

A critical finding in AKI is inappropriately dilute urine — a dehydrated cat should be concentrating urine maximally (specific gravity above 1.035). In AKI, the damaged kidneys cannot concentrate, so urine specific gravity is often 1.008–1.015 or lower despite obvious dehydration. This same finding occurs in CKD, but in the context of a previously normal cat presenting acutely, it is highly significant. Urinalysis may also show casts (cylindrical debris from damaged kidney tubules), protein, blood, and white cells (if infection is present). Calcium oxalate crystals in the urine of an acutely ill cat raise strong suspicion for antifreeze toxicity.

Treatment of AKI in Cats

AKI treatment is intensive and requires hospitalization. The pillars are:

1. Aggressive IV Fluid Therapy

The foundation of all AKI treatment is IV fluids — typically isotonic crystalloids (Lactated Ringer's or 0.9% NaCl) at rates carefully calculated to replace deficits, correct dehydration, and promote urine output (diuresis to flush toxins). The rate is adjusted based on urine output monitoring and response to treatment. Cats that are producing urine (non-oliguric) respond better than those that are oliguric or anuric. Fluid overload is a risk, especially in cats with cardiac disease — monitoring for lung sounds and respiratory rate is essential.

2. Treat the Underlying Cause

IV fluids alone are not enough if the cause is still present. Depending on the cause:

• Lily toxicity: Induce vomiting and activated charcoal if very recent; aggressive IV diuresis; there is no specific antidote
• Antifreeze (ethylene glycol): Fomepizole (4-MP) or ethanol IV — must be given within 3–6 hours to be effective
• Urinary obstruction: Urethral unblocking under sedation; urinary catheter placement to allow drainage
• Pyelonephritis: Culture-guided IV antibiotics — typically ampicillin or enrofloxacin initially, then adjusted based on culture results
• NSAID toxicity: Stop the drug; IV fluids; GI protectants (sucralfate, omeprazole)

3. Supportive Care

Prognosis and Recovery

Prognosis in AKI is highly cause-dependent:

• Pre-renal AKI (dehydration, low blood pressure): Good to excellent with prompt IV fluid therapy — kidneys often recover fully
• Post-renal AKI (urinary obstruction): Good if unblocked within 24 hours; guarded if blocked 48+ hours; poor if kidney damage is severe
• Lily toxicity (treated within 18 hours): Good — can make a full recovery
• Lily toxicity (established kidney failure): Guarded to poor — hemodialysis may offer the best chance
• Antifreeze toxicity: Very poor — irreversible damage occurs rapidly
• Pyelonephritis: Good with appropriate antibiotics if no pre-existing CKD; guarded if CKD is present

Cats that survive AKI may recover normal kidney function, or may retain some degree of lasting kidney injury — effectively transitioning to CKD. Regular monitoring of kidney values, blood pressure, and urine specific gravity is recommended for all AKI survivors.

Frequently Asked Questions