Winterization is in full swing here in Colorado, and this is when I worry most about pets getting into antifreeze. While a vehicle needs antifreeze no matter what the outside temperature, most folks tend to replace antifreeze before cold weather takes hold, particularly in the parts of the country that can experience extreme winter weather. I thought I’d take this opportunity to review the essentials of antifreeze (ethylene glycol) poisoning in pets.

Ethylene glycol (EG) is a colorless, almost odorless (to humans anyway), sweet-tasting alcohol that is found in most types of antifreeze. When ingested, it is rapidly absorbed from the gastrointestinal tract. Clinical signs may develop within one hour of ingestion because of the chemical’s ability to move from the bloodstream into the cerebrospinal fluid that bathes the brain. Peak blood concentrations are often measured within six hours of ingestion. Ethylene glycol is metabolized by the liver, forming glycoaldehyde, glycolic acid, and glyoxylic acid, the presence of which causes the body to become more acidic than normal. Glyoxylic acid then combines with other substances to form calcium oxalate crystals that severely damage the kidneys as they move from the blood into the urine.

The minimum lethal dose of ethylene glycol in dogs is 2-3 ml/lb and only 0.68 ml/lb in cats. In simpler terms, a teaspoon-full is enough kill to kill a cat.

Ethylene glycol toxicity is divided into three stages:

• Stage 1 — Central Nervous System Signs (30 min - 12 hrs)
• Stage 2 — Heart and Lung Signs (12-24 hrs)
• Stage 3 — Kidney Signs (24-72 hrs)

Symptoms can include depression, vomiting, loss of appetite, unsteadiness when walking, low body temperature, abdominal pain, increased thirst and urination, and a high heart rate. Later in the course of the disease, pets may develop oral ulcers and seizures and produce little or no urine.

Laboratory values (blood work and urinalysis) in pets that have ingested antifreeze are consistent with acute kidney failure (e.g., increased blood urea nitrogen and creatinine and low urine specific gravity) as long as enough time has passed for kidney damage to occur. A very high anion gap (more negative ions in the blood than is normal), acidic blood, low blood calcium levels, high blood sugar and phosphorous levels, and the presence of calcium oxalate crystals in the urine are all suggestive of ethylene glycol poisoning, but a definitive diagnosis in a live animal is usually made through the use of a bench top test that looks for the presences of the toxin in a sample of blood.

Unfortunately, ethylene glycol tests can be falsely negative in cats because of the small amount of toxin that may be involved or late in the course of the disease when little unmetabolized ethylene glycol is left in the body. False positive are also possible when pets have received activated charcoal or diets or medications that contain propylene glycol. EG tests run through human hospitals may be helpful in complicated cases. A wood’s lamp can also be used to detect the fluorescent dye that is added to many types of antifreeze. It may be visible in the mouth, material that is vomited, or in urine, but only soon after ingestion (six hours in the case of urine). False positives and negatives are also possible when using a wood’s lamp, so diagnosis should not be based on the presence or absence of fluorescence alone.

Tomorrow: Treating and Preventing Antifreeze Poisoning in Pets

Dr. Jennifer Coates

Image: Earth Week 1 by Nick Harris / via Flickr