Increased Thirst (Polydipsia) in Cats — Symptom Assessment Guide

A practical owner’s guide to increased thirst (polydipsia) in cats: what it looks like, common causes (CKD, diabetes, hyperthyroidism), home checks, decision tree and when to seek urgent care.

Quick Assessment

• Is this an emergency?

• Most common cause (older cats): chronic kidney disease (CKD), diabetes mellitus, or hyperthyroidism — these three dominate the differential list for senior cats.
• When to see a vet: any persistent increase in drinking for more than 48–72 hours, or sooner if accompanied by weight loss, increased urination, vomiting, poor appetite, or abnormalities on home checks.

What increased thirst (polydipsia) looks like

Polydipsia means drinking more water than normal. You may notice:

• Empty or frequently refilled water bowl(s) — the bowl needs topping up more often than usual.
• Drinking from unusual places (sinks, toilet, puddles).
• More frequent trips to the litter box and larger wet clumps of urine.
• Behavior changes: restlessness, increased vocalisation, appetite change, or hiding.

• Normal: roughly 40–60 mL/kg/day (varies with diet — cats fed dry food drink more).
• Polydipsia commonly suspected when intake exceeds ~100 mL/kg/day or you observe a clear doubling of usual intake (for an average 4–5 kg cat, >200–300 mL/day is a reasonable rule-of-thumb). [Merck Vet Manual]

Possible causes — ranked by likelihood (older cats first)

(References: Merck Veterinary Manual — polyuria/polydipsia and disease-specific pages.)

Decision tree — quick symptom → likely cause → what to do

• If polydipsia + increased urination but cat otherwise bright and losing weight slowly → likely chronic kidney disease or early hyperthyroidism.

• If polydipsia + polyphagia (increased appetite) + rapid weight loss + poor grooming + possible sweet/acetone breath → likely diabetes mellitus.

• If polydipsia + weight loss + increased activity/vocalisation + tachycardia or heart murmur → likely hyperthyroidism.

• If polydipsia + fever (>103°F / 39.4°C), painful urination, or signs of systemic illness → consider urinary tract infection / pyelonephritis or other infection.

• If polydipsia + recent steroid or diuretic medications → likely medication effect.

• If polydipsia + vomiting, lethargy, collapse, or neurologic signs → emergency (diabetic ketoacidosis, severe dehydration, or other critical disease).

Home assessment steps (what to check and how to measure)

When it's an emergency — red flags

Go to an emergency clinic immediately if your cat has any of the following:

• Collapse, severe weakness or inability to stand.
• Seizures or severe disorientation.
• Rapid, labored breathing.
• Continuous vomiting and unable to keep fluids down.
• Sweet/acetone (fruit-like) breath, excessive lethargy, or rapid breathing — signs of diabetic ketoacidosis.
• Positive home glucose reading >300 mg/dL (if you use a pet glucometer) or positive urine ketones.
• Severe dehydration signs (sunken eyes, tacky/dry gums, skin that stays tented) — dehydration >8% is life-threatening.

When to schedule a vet visit (non-urgent but required)

• Any sustained increase in drinking lasting more than 48–72 hours.
• Increased water intake plus any of: increased urination, weight loss, appetite change, vomiting, diarrhea, or behavior change.
• If you measured water intake >100 mL/kg/day or a clear doubling from baseline.
• If your cat is older (>7–8 years) — because CKD, diabetes and hyperthyroidism are common and screening is advised.

Home care — safe steps while you arrange veterinary care

• Continue to offer fresh water and encourage drinking; do not restrict water.
• Offer wet (canned) food to increase water intake and reduce kidney workload if CKD is suspected.
• Do not give insulin, thyroid or other prescription medications without veterinary diagnosis and dosing.
• Avoid over-the-counter diuretics or human medications.
• Keep the environment calm and ensure easy access to litter boxes and water bowls.
• Record a 48–72 hour diary of water intake, urine frequency, appetite, vomiting and weight changes to share with the vet.

What your veterinarian will likely do (tests and next steps)

Your vet will not rely on thirst alone. Initial diagnostics commonly include:

• Physical exam (including heart rate, pulse quality, thyroid palpation, and blood pressure).
• Blood tests: CBC, serum chemistry (BUN, creatinine), electrolytes, glucose, and often SDMA to screen kidney function.
• Total T4 (thyroid) test in older cats.
• Urinalysis with urine specific gravity (concentrating ability), dipstick for glucose/ketones, sediment exam and possibly urine culture.
• Additional testing: fructosamine (if diabetes suspected), urine culture (if infection suspected), abdominal ultrasound or imaging for further assessment.

What to tell your vet — the essential information

Bring or be ready to report:

• Duration of increased thirst (when you first noticed it).
• Exact or estimated daily water intake (mL/day) and changes compared with baseline.
• Changes in urination frequency and volume, litter box observations.
• Appetite changes (increased vs decreased), vomiting, diarrhea, weight loss and activity level.
• Any medications or supplements your cat is taking (especially steroids, diuretics, or thyroid meds) and recent vaccinations.
• Whether your cat is indoor/outdoor, access to toxins, and whether the cat is intact (unspayed female can get pyometra).
• If you have a urine sample, bring it chilled in a sealed container.

Closing points — what to expect and why swift evaluation matters

In older cats, increased thirst is often an early sign of systemic disease — most commonly CKD, diabetes mellitus, or hyperthyroidism. These conditions are manageable when diagnosed early, and initial testing is straightforward and informative. Timely veterinary assessment helps prevent complications such as severe dehydration, diabetic ketoacidosis, or progressive kidney injury.

Remember: this guide helps you assess urgency and prepare — it is not a diagnosis. If in doubt, call your veterinarian; early testing is usually simple (bloodwork and urinalysis) and can provide rapid answers.

Primary citation

Merck Veterinary Manual — sections on polyuria/polydipsia, chronic kidney disease, diabetes mellitus and hyperthyroidism in cats: https://www.merckvetmanual.com/

Frequently Asked Questions