Onion toxicity results in hemolysis, or the breakdown of red blood cells. As the cells break down, the feline has less red blood cells circulating in the body, creating signs of weakness and panting due to the fact that these cells serve to carry oxygen. Onion toxicity can be fatal in cats if immediate veterinary care is not sought.

Onion toxicity in cats is a hypersensitive reaction of the feline’s red blood cells to the oxidant present in fresh or dried onions. An onion can become toxic to a feline if more than 1 gram per 5 pounds of body weight is ingested. Onion powder has a high toxicity rate and is potentially more potent than a fresh onion. The toxic agent present in onions is the oxidant n-propyl disulfide. 

Common clinical signs noted after a feline has ingested onion includes: 

An onion can become toxic to a feline if more than 1 gram per 5 pounds of body weight is ingested. Onion powder has a high toxicity rate and is potentially more potent than a fresh onion. 

Onion toxicity in cats is caused by the oxidant present in onions, n-propyl disulfide. Cats have a high sensitivity for red blood cell oxidation, due to the larger surface area for oxidizing agents to attach to the cell. When the oxidant, n-propyl disulfide is digested and enters the bloodstream, the body interprets this irregular oxidant as a foreign invader. As the oxidant has already attached to the red blood cell and cannot readily be removed, the body destroys the cells in an attempt to remove the harmful substance. The end result is hemolysis, or the breakdown of red blood cells. 

The veterinarian will begin the diagnostic process with a physical examination and a review of your cat’s medical history. He or she will ask about your cat’s current diet, including table scraps or ingredients in her raw food diet. 

Onion toxicity in cats is commonly diagnosed through the examination of a cat’s red blood cells. As hemolytic anemia is a common clinical sign of onion toxicity, the present of Heinz bodies on the edge of a red blood cell, seen microscopically, will indicate oxidative injury. The diagnostic tool to reveal this clinical sign is called a blood smear, requiring only a small sample of blood from the feline. 

Hemolytic anemia is also a clinical sign of several other common feline diseases, so your veterinarian will likely request a biochemistry profile orimaging to complete the differential diagnosis.

No specific antidote is available for onion toxicity and the condition is mainly treated with supportive care. The feline may be hospitalized and administered intravenous fluid therapy. The fluid therapy is used to flush the body of the toxin and give the body time to stop hemolyzing its red blood cells. In most cases, once the ingestion of the toxin has ceased, the cat’s bone marrow will begin creating new, healthy red blood cells to replace the previously destroyed cells. In severe blood loss cases, the feline may require a blood transfusion to replenish the body’s blood supply.

Improvement following treatment of onion toxicity will be seen within hours to a day, depending on the cat’s toxic state. Once the feline is stable, the veterinarian may choose to run additional lab work including examination of the blood and urine to ensure the body’s organs are functioning at full capacity. Follow-up appointments are not necessarily required, but the veterinarian may choose to have your cat reevaluated if a blood transfusion was required in the treatment process. 

To avoid onion toxicity in cats, pet owners should avoid feeding table scraps and baby food to the feline. Cats do not usually eat onion by itself, but mixed into a food, it can easily be ingested. Always keep fresh onions, onion powders, onion salts and other products containing onion out of your cat’s reach.