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What is Onion Toxicity?

Onion toxicity results in hemolysis, or the breakdown of red blood cells. As the cells break down, the feline has less cell circulating in the body, creating signs of weakness and panting due to the fact that these cells 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 caused by the oxidant n-propyl disulfide. 

Onion Toxicity Average Cost

From 288 quotes ranging from $500 - $4,000

Average Cost

$2,000

Symptoms of Onion Toxicity in Cats

The symptoms associated with onion toxicity in cats are paired with those found in an allergic reaction caused by an ingested agent. Common clinical signs noted after a feline has ingested onion includes: 

  • Panting 
  • Elevated heart rate 
  • Weakness 
  • Hematuria (blood in the urine) 
  • Hemolytic anemia (breakdown of red blood cells)
  • Heinz body anemia (breakdown of red blood cells)
  • Vomiting 
  • Gastrointestinal upset 
  • Asthmatic attacks 
  • Allergic reaction 
  • Liver damage 
  • Diarrhea 
  • Decreased appetite 
  • Lethargy 
  • Contact dermatitis (skin exposure) 
  • Fainting 
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Causes of Onion Toxicity in Cats

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. 

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Diagnosis of Onion Toxicity in Cats

The veterinarian will begins the diagnostic process with a physical examination and a review of your cat’s medical history. He or she will ask you 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 or radiographs to complete the differential diagnosis.

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Treatment of Onion Toxicity in Cats

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.

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Recovery of Onion Toxicity in Cats

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.

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Onion Toxicity Average Cost

From 288 quotes ranging from $500 - $4,000

Average Cost

$2,000

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Onion Toxicity Questions and Advice from Veterinary Professionals

Need pet health advice? Ask a vet

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Tabby cat

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3month

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Unknown severity

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10 found helpful

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I think my cat might ate a little piece of onion what can I give her at home

Aug. 6, 2020

Owner

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Dr. Michele K. DVM

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0 Recommendations

Thank you for your question. That small amount of onion should not cause any toxicity for your kitten, and she will probably be okay. It would be best to monitor her for any signs of vomiting, diarrhea, lethargy, or loss of appetite, if she does have a GI upset from the onion, and if any of those occur, have her seen by a veterinarian. Otherwise, I think she will be okay.

Aug. 6, 2020

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Siamese cat

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Seven Weeks

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Unknown severity

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Vomiting, Lethargy

I gave my cat some licks of mashed potatoes off my finger, the mashed potatoes included cheddar cheese, milk, cheese, sour cream, a little bit of green onion and salt and pepper. I made sure she didn’t eat any green onion but she is vomiting now????

Aug. 5, 2020

Owner

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Dr. Michele K. DVM

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Thank you for your question. That may have been too rich for her, and it may have upset her stomach. If she continues to vomit, it would be best to have her seen by a veterinarian, as she may need treatment to help settle her stomach. They will be able to see what might have caused this and get medication for her so that she feels better. I hope that all goes well for her!

Aug. 5, 2020

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Domestic Cat

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Seven Years

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1 found helpful

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None

Woke up to find my cat gotten into the trash and ate three dry rub bbq ribs. I have searched online to see what I should look out for but would really like to speak with someone.

July 27, 2020

Owner

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Dr. Michele K. DVM

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Thank you for your question. This may cause significant GI upset, and it would be a good idea to watch for any signs of vomiting, diarrhea, lethargy, or loss of appetite in your cat. If any of those things happen, it would be best to take him/her to see a veterinarian as soon as possible. They will be able to help give treatment if any of those signs do occur. I hope that all goes well with your cat!

July 27, 2020

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Cat - domestic short hair

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Fifteen Years

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6 found helpful

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My cat ate a sliver of cooked onion. Should I be worried?

July 14, 2020

Owner

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Dr. Michele K. DVM

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Thank you for your question. That small amount of onion should not be harmful to your cat other than to possibly cause mild GI upset. If he has any signs of vomiting, diarrhea, loss of appetite or lethargy, then it would be best to have him seen by your veterinarian. I would be surprised if any of those signs happened, however. I hope that all goes well for him.

July 14, 2020

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Finnick

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Russian Blue mix

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1 Year

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Moderate severity

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None At The Moment

I had a salad with a lot of onion in it, I left the room for a second. But when I came back my cat had his head in the bowl and as I went to take the bowl away he pulled out a large piece of onion. I did take it away, but do I need to worry? It has only been about 30 minutes and he is acting fine right now, but can't it take hours to days for symptoms to show up?

Sept. 21, 2018

Finnick's Owner

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Lincoln/Link

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DOMESTIC

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10 Months

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Fair severity

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A Little Slow

My mate Lincoln is a little rascal and will get into any food he can. he rips opens plastic rubbish bags and jumps at any chance to eat anything that might have fallen on the floor. he gets especially excited when me and me mum have dinner. he waits til we've finished and not paying attention, then steals whatever he can off our plates. yesterday he snuck up to my mums plate and stole something. i asked her what it was and she said it was just a bit of onion. i had that moment where i just sat as if nothing was wrong, it was just a second, before i yelled and leapt right up from my chair to rush over to him and grab it from him. he ended up wolfing it down and running off. i knew there was no point trying to get it out because it would be gone by then. it was a sliver of onion, about as long as your middle finger, and thick in the middle tapering off at both ends. Lincoln is about 0 months and very slightly smaller than average size, just a little bit. my mum didnt know onions were toxic to cats, and i think because of my initial shock, i yelled and accused her of being careless. because of being accused so, i think she in retaliation is acting as if it isnt a big deal. i quickly called the emergency vet to ask if he would be ok. the vet said he'll probably be ok, and to check his tongue colour and keep an eye on him for signs of slowing down. ive checked his tongue, it still seems like his usual pale pink colour. and when i came home today i tried to check his response by plying with his favourite toy. he was rather slow trying to play with it, but i wonder if thats because he broke it yesterday. pulled the string out of it so i wonder if its just not as interesting. i did do all the calling the vet, checking his behaviour, and quickly picking up food that falls. but i wanted to know your opinions, should i take Link to the vet? maybe just a check up? i was considering getting a check up a week from now anyways.

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jenny

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Unknown

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3 Years

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None Yet

I was having some soup with scallions in it, I left for a second and when I came back my cat was lapping the broth. I'm guessing it was no more than 1/2 tsp worth. Would anything toxic be diluted? she's about 12 lbs.

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charlie

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lynx siamese

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1 Year

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Fair severity

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None

i feed my cat a few sour cream and onion chips ................................................................................................................................................................................................

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Trout

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Tabby Cat

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3 Years

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Mild severity

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Mild severity

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Hides, Vomiting,Different Hart Bet

Hi It was lunch and my mom came home from work and she had a salad and she gave the cat a onion and I said “Is that toxic for cats mom?” She said that she “l did not know.” His name is trout and the size of the onion is smallish. There has been weird behavior that day he would hide in the basement and he would vomit I Hope is gets better I have been searching on the Internet for a while. I am crying every night in bed thinking that he would die I am only 12 and I don’t want to lose my kitty I have a another Cat tuna he is fine.

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Kaneki

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Unknown

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2 Months

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My kitty was playing around with my friend while she was eating a burger about 30 minutes ago and ate a little bit of the onion she took off of it. it was only about 1 inch long and very thin, but i’m worried. he seemed to like it, he was purring and acting really hyper. I read that onions are toxic to cats, and i’m scared that since he is so young it will affect him worse. Should I be concerned?

Onion Toxicity Average Cost

From 288 quotes ranging from $500 - $4,000

Average Cost

$2,000