Ethylene glycol (antifreeze) test in dogs and cats
Ethylene glycol is the poisonous substance in antifreeze, and dogs and cats are the animals most often affected; younger animals may be more susceptible. The test looks for it in the blood, but it works only in the first hours after the animal swallowed it. A positive result needs confirmation, and a negative one late after the event rules out nothing.
What it shows
The in-clinic test is a point-of-care, semiquantitative colorimetric test on serum. It detects ethylene glycol from 20 mg/dL and is meant to be run between 1 and 10–14 hours after the animal swallowed it; results are best within 1–6 hours. In-clinic tests are less sensitive and specific than the quantitative test done in a human hospital or reference laboratory, which is the reference method; some human hospital labs accept samples from animals.
A combined in-clinic test also measures oxalate in the plasma, a product of ethylene glycol breakdown, at 8–10 hours and up to 24–36 hours after swallowing. Because the window is so short, vets also rely on the history, the exam and other blood and urine tests.
Higher than reference — what it may be a sign of
- Positive. Ethylene glycol in the blood above the test’s limit. It fits poisoning when the history and signs fit: early nervous-system and digestive signs, from 30 minutes to 12 hours after swallowing, look like alcohol intoxication; a short apparent recovery may follow before kidney failure develops.
- False positive. Swallowing propylene glycol can make an ethylene glycol test kit turn positive. The quantitative hospital test removes such false results.
If poisoning is suspected — go to the vet right away, do not wait for the test.
Lower than reference
A negative result is the expected one, but it does not settle the question by itself. An in-clinic test is less sensitive than a hospital test, and it is designed for the first hours: run outside its time window, a negative result does not answer the question. The vet reads it together with the history, the anion gap, urine crystals and kidney values.
Look at together with
- Anion gap — within 3 hours of a toxic amount dogs and cats develop metabolic acidosis with a raised anion gap; ethylene glycol and its breakdown products are among the acids that raise it. A raised osmole gap in the blood appears in the same early window.
- Calcium oxalate crystals — monohydrate crystals are seen most often, and the picket-fence form is the more specific for this poisoning; the dihydrate form also occurs, but it can also form in stored urine. Crystals are not seen in every affected animal: one guidance notes them in only about 40% of cases.
- Urine specific gravity and urine pH — urine is typically poorly concentrated or isosthenuric and acidic.
- Creatinine and urea — rise when the kidneys fail, and the amount of urine may drop.
Units and conversion
The result is qualitative and has no unit in the app. The form says positive or negative (sometimes detected or not detected). A semiquantitative test can show whether the level is above set marks; for this test the marks of 20 mg/dL and 50 mg/dL are described. A quantitative hospital test prints a concentration in mg/dL. In the app the result is stored as text.
Reference range
The reference is on your lab’s form; for this test it is “negative” or “not detected”. For a quantitative test done at a human hospital, the ASPCA poison-control guidance counts a level below 50 mg/dL as negative for dogs and below 20 mg/dL as negative for cats. The Merck Veterinary Manual ties the same two marks to the minimum lethal level in cats (20 mg/dL) and in dogs (50 mg/dL). A positive result is read together with the history, the signs and the other tests.
Cats and dogs
A smaller amount of ethylene glycol is lethal for a cat than for a dog. Everything also happens faster in cats: oxalate crystals can appear in the urine as early as 3 hours after swallowing, and signs of kidney failure appear 12–24 hours after. The lower limit of in-clinic tests sits exactly at the level described as the minimum lethal one for cats, so in a cat the timing of the test matters especially.
In dogs, oxalate crystals can appear in the urine from about 6 hours after swallowing, and signs of kidney failure appear 36–72 hours after. The minimum lethal level for dogs (50 mg/dL) is above the lower limit of in-clinic tests.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- Regehr T. Ethylene Glycol Toxicosis in Animals. Merck Veterinary Manual, professional version, full review January 2022, last updated September 2024.
- Propylene Glycol Toxicosis in Animals. Merck Veterinary Manual, professional version.
- ASPCApro (ASPCA Animal Poison Control Center). Ethylene Glycol and Antifreeze Poisoning in Pets, last modified February 2024.
- eClinPath (Cornell University). Urinalysis — Crystals (calcium oxalate monohydrate and dihydrate).
- eClinPath (Cornell University). Anion gap.
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.