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POISONING · DOGS

Antifreeze poisoning in dogs: signs, tests and outlook

Antifreeze contains ethylene glycol, a sweet-tasting liquid that can destroy the kidneys within days. The first signs look like drunkenness and can fade, which gives a false sense of safety. Tests can pick up the poison early, and an antidote exists, but it only works if it is given within hours.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Ethylene glycol poisoning is a time-critical emergency. In the first 12 hours a dog may wobble, vomit and drink a lot; kidney failure follows 36 to 72 hours after drinking. Early on, blood tests show a high osmolal gap and an acid build-up; later, calcium oxalate crystals appear in the urine and kidney values rise. Dogs treated before kidney damage sets in usually survive; once the kidneys fail, few do.

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What antifreeze does to a dog

Concentrated antifreeze can contain up to 95% ethylene glycol. It tastes sweet and a small amount is enough to kill. In the United States a bittering agent has been added since 2012, but some animals may still drink it [1]. Cases peak in fall, winter and early spring in cold climates [1], though they are seen in every season [5].

Ethylene glycol itself acts like alcohol. The danger comes from what the liver makes of it: glycolic acid and oxalate. These acids lower blood pH and damage the kidney tubules, and oxalate binds calcium to form calcium oxalate crystals inside the kidneys [1].

Cats are even more sensitive: the minimum lethal dose of undiluted ethylene glycol is about 1.4 mL/kg in cats against 4.4–6.6 mL/kg in dogs [1]. Whatever the amount, call your vet or an emergency clinic straight away.

Signs and timeline

Timeline in dogs. In cats, kidney failure comes earlier, at 12 to 24 hours [1].
Time after drinkingWhat owners may see
30 minutes to 12 hoursLooks drunk: wobbling, depression, vomiting, drinking and urinating a lot [1].
Around 12 hoursA brief apparent recovery may occur [1]. The danger is not over.
36 to 72 hoursAcute kidney failure: little or no urine, painful kidneys, fast heart and breathing rates, vomiting, mouth ulcers, then seizures, coma and death [1].

If you saw your dog drink antifreeze, or find a spill and a wobbly dog, go to a vet at once. Do not wait for signs.

What the blood and urine tests show

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
OG Osmolal gap (calculated)48mOsm/kg< 10H
  1. Abbreviation OG or Osm gap: measured osmolality minus the osmolality calculated from sodium, glucose and BUN.
  2. Result 48 mOsm/kg in this illustrative line: clearly high. In one study, a charcoal suspension containing propylene glycol raised the gap in dogs from 5 to 52 mOsm/kg, so the history matters [10].
  3. Unit mOsm/kg (milliosmoles per kilogram of water).
  4. Laboratory interval An illustrative interval. The normal gap depends on the formula the clinic uses [14].
  5. Flag H: above the interval. With a wobbly dog and possible antifreeze exposure, vets treat this as an emergency. Later, look for crystals in the urine and for calcium changes.
  • High osmolality and osmolal gap from the first hour: the unmeasured ethylene glycol adds particles to the blood [2].
  • Metabolic acidosis with a high anion gap within about 3 hours, as the acids build up [1, 2, 7].
  • Dilute urine (low urine specific gravity, often isosthenuria) with an acidic pH [1, 3]. See urinalysis in dogs and cats.
  • Calcium oxalate crystals in the urine from about 6 hours in dogs, mostly the monohydrate form [1, 2]. They signal a poorer outlook [1].
  • Low calcium, high phosphate and high glucose on the chemistry panel; ionized calcium is the preferred measure [1, 3].
  • Rising creatinine and BUN (azotemia) often not until about 48 hours, once the kidneys are failing [2, 3]. See creatinine in dogs.
  • Blood count: high neutrophils and low lymphocytes are common [3].

How vets confirm antifreeze poisoning

  • Ethylene glycol test kits: quick clinic tests detect from 20 mg/dL. They work best between 1 and 10–14 hours after drinking, before the poison is fully converted [1]. Kits differ in accuracy [13].
  • False positives: other substances can react. A dog that drank propylene glycol tested positive on a clinic kit [9]. A reference laboratory can measure the exact level [1].
  • Blood gas, chemistry and urinalysis together: acidosis, a high gap and crystals support the diagnosis when no kit is available [1, 5].
  • Urine crystals: the “picket fence” calcium oxalate monohydrate crystals are typical but not seen in every poisoned dog, and they can occur with high urine calcium from other causes [6, 8]. Calcium oxalate is also a common bladder stone type, so crystals are read with the rest.
  • Wood’s lamp: some antifreeze contains a dye that glows in urine under UV light. In a human study, doctors spotted it in only 35% of positive samples, so a negative result does not rule poisoning out [11].
  • Vets start treatment on suspicion if a reliable test is not available fast [1].

Outlook: hours matter

The outlook depends on how fast treatment starts [1]. An antidote exists that stops the body from turning ethylene glycol into its toxic acids, but it only helps before much of the poison has been converted. In 37 dogs with confirmed poisoning, all 16 that never developed raised kidney values survived; of the 21 that did, only 1 survived. Dogs treated within 8 hours had a good prognosis [4].

Late arrival is the main reason dogs die. In an older series, 78% of dogs and cats died, mainly because of delays [3]. In a recent Canadian series, 33% of dogs survived to discharge, and many were brought in more than 8 hours after signs began [5]. For cats the window is even shorter: in a study, cats survived when the antidote was given within 3 hours [12].

Once the kidneys fail, outlook is poor [1]. Read more about kidney disease in dogs.

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En français : antigel et chien.

Questions to ask your veterinarian

  1. Can you run an ethylene glycol test now, and is it still in the right time window?
  2. What do the blood gas, anion gap and osmolal gap show?
  3. Are there calcium oxalate crystals in the urine, and what is the specific gravity?
  4. Are the creatinine, BUN, calcium and potassium normal yet, and when will you recheck them?
  5. Is my dog still early enough for the antidote, and what is the expected outlook?
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Frequently asked questions

What are the three stages to ethylene glycol poisoning?

In dogs, a drunk-like stage with vomiting and thirst from 30 minutes to 12 hours, a short apparent recovery around 12 hours, then acute kidney failure with fast heart and breathing rates at 36 to 72 hours [1].

Can a dog be saved from antifreeze poisoning?

Yes, if treatment starts early. Dogs treated within 8 hours had a good prognosis, while few dogs survived once kidney values had risen [4].

What are the first signs of antifreeze poisoning in dogs?

Signs similar to drunkenness: wobbling, depression and vomiting, with more drinking and urinating [1, 2].

How long does it take for antifreeze poisoning to show?

Signs can start within 30 minutes [1]. Blood changes such as a high osmolal gap appear in the first hour, but kidney values may not rise until about 48 hours [2].

Are cats more sensitive to antifreeze than dogs?

Yes. The minimum lethal dose is lower in cats, and their kidney failure comes earlier, at 12 to 24 hours [1].

Sources

  1. Regehr T. Ethylene Glycol Toxicosis in Animals. Merck Veterinary Manual. Updated 2024. merckvetmanual.com/toxicology/ethylene-glycol-toxicosis/ethylene-glycol-toxicosis-in-animals
  2. Grauer GF et al. Early clinicopathologic findings in dogs ingesting ethylene glycol. Am J Vet Res. 1984;45(11):2299-2303. pubmed.ncbi.nlm.nih.gov/6524724
  3. Thrall MA, Grauer GF, Mero KN. Clinicopathologic findings in dogs and cats with ethylene glycol intoxication. J Am Vet Med Assoc. 1984;184(1):37-41. pubmed.ncbi.nlm.nih.gov/6698834
  4. Connally HE et al. Safety and efficacy of 4-methylpyrazole for treatment of suspected or confirmed ethylene glycol intoxication in dogs: 107 cases (1983-1995). J Am Vet Med Assoc. 1996;209(11):1880-1883. pubmed.ncbi.nlm.nih.gov/8944802
  5. Sauder T et al. A retrospective case series of companion animals hospitalized for ethylene glycol poisoning at a Canadian veterinary teaching hospital. Can Vet J. 2026;67(5):553-562. pubmed.ncbi.nlm.nih.gov/42095169
  6. eClinPath, Cornell University College of Veterinary Medicine. Crystals. eclinpath.com/urinalysis/crystals
  7. eClinPath, Cornell University College of Veterinary Medicine. Anion gap. eclinpath.com/chemistry/acid-base/chemistry-tests/anion-gap
  8. Thrall MA, Dial SM, Winder DR. Identification of calcium oxalate monohydrate crystals by X-ray diffraction in urine of ethylene glycol-intoxicated dogs. Vet Pathol. 1985;22(6):625-628. doi.org/10.1177/030098588502200618
  9. Claus MA, Jandrey KE, Poppenga RH. Propylene glycol intoxication in a dog. J Vet Emerg Crit Care. 2011;21(6):679-683. doi.org/10.1111/j.1476-4431.2011.00688.x
  10. Burkitt JM et al. Effects of oral administration of a commercial activated charcoal suspension on serum osmolality and lactate concentration in the dog. J Vet Intern Med. 2005;19(5):683-686. doi.org/10.1892/0891-6640(2005)19[683:eooaoa]2.0.co;2
  11. Wallace KL et al. Diagnostic use of physicians’ detection of urine fluorescence in a simulated ingestion of sodium fluorescein-containing antifreeze. Ann Emerg Med. 2001;38(1):49-54. doi.org/10.1067/mem.2001.115531
  12. Connally HE, Thrall MA, Hamar DW. Safety and efficacy of high-dose fomepizole compared with ethanol as therapy for ethylene glycol intoxication in cats. J Vet Emerg Crit Care. 2010;20(2):191-206. doi.org/10.1111/j.1476-4431.2009.00492.x
  13. Creighton KJ et al. Evaluation of two point-of-care ethylene glycol tests for dogs. J Vet Emerg Crit Care. 2014;24(4):398-402. doi.org/10.1111/vec.12203
  14. Dugger DT et al. A comparison of the clinical utility of several published formulae for estimated osmolality of canine serum. J Vet Emerg Crit Care. 2014;24(2):188-193. doi.org/10.1111/vec.12153

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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