The longer you wait to take your cat to a veterinarian, the worse his symptoms may become. To avoid complications, take your cat to a veterinarian as soon as possible after you spot the symptoms of onion poisoning.

Many people use onions to add flavor to their favorite dishes, but unfortunately, onions are toxic to various animals, including cats. In fact, it is believed that cats are more sensitive to the toxins of onions than other animals such as dogs or horses. Even a small amount of the bulb, flower, or stem of an onion can trigger a response in your cat. Once it is consumed, the onion causes oxidative damage to your cat’s red blood cells, which impacts the bloodstream’s ability to transport oxygen to different organs in the body. This condition, known as Heinz body anemia, can be incredibly dangerous.

Some cats begin to experience symptoms of onion poisoning soon after ingestion, however other cats may not exhibit any symptoms for several days. Some of the most common symptoms to look for include:

Onion poisoning occurs after a cat consumes onion, which can be poisonous in both fresh and dried forms. Every part of the onion, including the bulb, flowers, and stem, are toxic to cats. 

An onion can cause oxidative damage to red blood cells, known as Heinz body anemia, making it impossible for the cat’s bloodstream to transport oxygen to different parts of the body. 

If you see your cat eating onion or if you notice any of the symptoms above, take him to a veterinarian as soon as possible for treatment. Talk to the vet about the symptoms you have observed, when they began, and if possible, when your cat consumed onion. 

The vet will begin by taking basic tests to look at the cat’s overall health. These tests include a complete blood count, blood chemistry profile, and urinalysis. These tests will show an abnormally low level of red blood cells, and when a blood sample is analyzed closely, the vet should be able to spot Heinz bodies, which indicates the cat is suffering from hemolytic anemia.  

A number of different conditions can cause hemolytic anemia, so the presence of Heinz bodies does not always lead directly to a diagnosis of onion poisoning. The vet will rely heavily on the symptoms you have described when making a diagnosis, so be as clear and informative as possible.

Treatment will begin immediately following the diagnosis of onion poisoning. They may induce vomiting if the timing is appropriate.  

If your cat’s skin has also come into contact with an onion, the vet will thoroughly bathe and scrub your cat to remove any toxins lingering on the skin. 

Many cats become dehydrated either before or during treatment because of the vomiting and diarrhea. If this happens to your cat, the vet will need to provide him with fluids via an IV. 

In extreme cases, the cat may have already lost too many red blood cells by the time you take him in for treatment. If this has happened to your cat, a complete blood transfusion may be necessary.

The sooner you take your cat to a veterinarian for treatment, the better his chances are of making a full recovery. If your cat has already suffered severe red blood cell loss by the time he receives treatment, his chances of recovering are much lower.

The vet may keep your cat following treatment to ensure he has been stabilized and no longer needs IV fluids or respiratory support. Once your cat has been released to you, discuss his diet with your vet. It’s important to remove any foods that may contain onion from your cat’s diet. In the days following treatment, the vet may recommend you stick to softer foods to avoid upsetting the cat’s sensitive stomach. Keep your cat comfortable and calm while he regains his strength over the next several days.

Make sure your cat does not have access to any onions. If you keep these out on your kitchen counter for cooking, put them in a safe place where cats cannot come into contact with them.