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Onion toxicity in dogs: Heinz bodies, anemia and blood work

Onions, garlic, leeks and chives can damage a dog’s red blood cells. The harm is often delayed: a dog may only vomit at first, then become pale, weak and pass dark urine a few days later. The blood count and a blood smear show what is happening to the red cells.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Onion and garlic contain sulfur compounds that oxidize red blood cells. The cells form Heinz bodies and eccentrocytes, then break down, causing an anemia that can appear one to several days after eating them. Cooked, dried and powdered forms are toxic too. Some Japanese breeds such as the Akita and Shiba are more sensitive, and cats more than dogs. Whatever the amount, contact your vet.

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Why onions and garlic harm red blood cells

Onion, garlic, leek and chives all belong to the Allium family. When they are chewed, they release sulfur compounds that oxidize red blood cells. This causes Heinz bodies and methemoglobin, a form of hemoglobin that cannot carry oxygen [1]. Cooking, drying and processing do not remove the toxic effect [1], and leftovers, pizza or dishes with onion powder can all be a source [2].

Most dogs recover with supportive care, and deaths are rare [3]. Still, in 69 dogs reported to a UK poison service from 1994 to 2008, 2 died and 2 were euthanized [1].

Repeated small meals may add up: daily feeding could have a cumulative effect on the red cells [2].

Why the anemia appears days later

Signs may start one day or several days after eating, depending on the amount [1]. The first signs are usually digestive: vomiting, diarrhea, belly pain, loss of appetite and dullness. Signs of red cell loss follow: pale gums, weakness, fast breathing and heart rate, jaundice and reddish or brown urine [1, 2].

Studies show the same delay on the blood tests. In dogs fed cooked onion for 2 days, red cell count, hemoglobin and hematocrit fell from day 1, with a clear drop by day 5; Heinz bodies peaked on day 3 [4]. In dogs given garlic extract for 7 days, the lowest red cell values came on days 9 to 11 [5].

What the blood count, smear and urine show

  • Low hematocrit (anemia): red cell count, hemoglobin and hematocrit fall over the following days [4]. Read more about anemia in dogs.
  • Heinz bodies: small clumps of damaged hemoglobin in the red cells. They are abnormal in dogs and show up best with a special stain (new methylene blue) [6].
  • Eccentrocytes: red cells whose hemoglobin is pushed to one side. They are often seen with Heinz bodies and are a hallmark of garlic and onion damage in dogs [5, 7, 9].
  • Reticulocytes (young red cells): in the onion study, they rose from day 1 and peaked on day 8, a sign that the bone marrow is responding (a regenerative anemia) [4, 6].
  • Methemoglobin: may be raised; the plasma can look brown [6]. One dog that ate baked garlic had a methemoglobin of 8.7% [8].
  • Bilirubin and urine: bilirubin rose on day 3 and urine urobilinogen on day 4 [4]. Red cells that burst in the blood release hemoglobin into the urine (hemoglobinuria), making it dark [6]. See urinalysis for dogs and cats.
  • White cells: high neutrophils and low lymphocytes may be seen [2].

Many sick dogs can have a few eccentrocytes for other reasons, so vets read the smear with the history and the complete blood count [7].

Reading the hematocrit on the report

A schnauzer seen 2 days after eating baked garlic had a regenerative anemia with a hematocrit of 22%, plus Heinz bodies and eccentrocytes on the smear [8]. The line below is an illustrative example.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
HCT Hematocrit22%35–57L
  1. Abbreviation HCT or Hct: the share of the blood made of red cells. PCV (packed cell volume) is a close equivalent.
  2. Result 22% in this illustrative line: a clear anemia. A comment such as “Heinz bodies and eccentrocytes present” points to oxidative damage.
  3. Unit %: the percentage of blood volume taken up by red cells. Some reports give it as a fraction (0.22 L/L).
  4. Laboratory interval An illustrative dog interval; each laboratory sets its own.
  5. Flag L: below the interval. A high reticulocyte count on the same report shows the marrow is responding [4, 6].

Amounts, garlic versus onion, and sensitive dogs

Amounts reported in studies: about 15–30 g of onion per kg of body weight caused clinically important blood changes in dogs, and about 5 g per kg in cats [1]. For garlic, about 5 g per kg is reported in dogs [3]. These figures are not a safe limit. A 20 kg dog died after eating garlic, with only about 16 g recovered from its stomach; the authors suggest individual sensitivity or incomplete recovery [3]. Contact your vet whatever the amount.

Reviews do not fully agree on which is worse. One review describes garlic as less toxic than onion in moderation [2], while the amount reported for garlic per kg is lower than for onion [3]. In the laboratory, dried and granulated garlic damaged dog red cells more than fresh garlic [11].

Some Japanese breeds, such as the Akita, Shiba and Jindo, can inherit red cells rich in glutathione and potassium, which makes them more sensitive [1]. In an experimental study, an onion compound caused a more severe anemia in dogs with this trait [10]. Cats are more sensitive than dogs [2].

How the vet confirms it

  • History: what was eaten, how much and when, including cooked dishes and powders [1].
  • Complete blood count with a smear: a regenerative anemia with Heinz bodies and eccentrocytes supports oxidative damage [6].
  • Repeat blood counts over the next days, since the lowest values can come several days later [4, 5].
  • Urinalysis and chemistry: hemoglobin in the urine and a rise in bilirubin fit red cell destruction [4, 6]. Your vet also considers other causes, such as immune-mediated hemolytic anemia.

There is no specific antidote. Care is supportive, and severely anemic dogs may need a blood transfusion [1].

Related articles

Other kitchen toxins: grapes and raisins and xylitol.

En français : oignon, ail et chien.

Questions to ask your veterinarian

  1. Is there anemia, and is it regenerative (are reticulocytes high)?
  2. Were Heinz bodies or eccentrocytes seen on the blood smear?
  3. Should we repeat the blood count, and when?
  4. Is methemoglobin raised, and does the urine contain hemoglobin?
  5. Is my dog’s breed more sensitive to onions and garlic?
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Frequently asked questions

Can a dog survive onion toxicity?

Yes, most do. Deaths are rare and most dogs recover with supportive care [3]. Severe cases can still be fatal: in one UK series of 69 dogs, 2 died and 2 were euthanized [1].

What is more toxic to dogs, onions or garlic?

Both damage red cells. The amount reported for garlic per kg (about 5 g/kg) is lower than for onion (15–30 g/kg) [3], although one review describes garlic as less toxic in moderation [2]. Avoid both.

Will a tiny bit of onion hurt my dog?

No safe amount has been established. A dog died after eating an amount of garlic below the reported toxic dose [3], and repeated small meals may add up [2]. Contact your vet whatever the amount.

How long after eating onion does a dog get sick?

Vomiting can come first; signs of anemia may take one to several days [1]. In a study, red cell values dropped clearly by day 5 [4].

What are Heinz bodies?

Small clumps of damaged hemoglobin inside red cells, caused by oxidation. They are abnormal in dogs and point to a toxin such as onion [6].

Sources

  1. Cortinovis C, Caloni F. Household Food Items Toxic to Dogs and Cats. Front Vet Sci. 2016;3:26. doi.org/10.3389/fvets.2016.00026
  2. Kovalkovičová N et al. Some food toxic for pets. Interdiscip Toxicol. 2009;2(3):169-176. doi.org/10.2478/v10102-009-0012-4
  3. Biasibetti E et al. Fatal Garlic (Allium sativum) Toxicosis in a Dog: Gross and Histopathological Findings in a Rare Case of Systemic Hemolytic Injury. Animals (Basel). 2026;16(11):1712. doi.org/10.3390/ani16111712
  4. Tang X et al. An experimental study of hemolysis induced by onion (Allium cepa) poisoning in dogs. J Vet Pharmacol Ther. 2008;31(2):143-149. doi.org/10.1111/j.1365-2885.2007.00930.x
  5. Lee KW et al. Hematologic changes associated with the appearance of eccentrocytes after intragastric administration of garlic extract to dogs. Am J Vet Res. 2000;61(11):1446-1450. doi.org/10.2460/ajvr.2000.61.1446
  6. eClinPath, Cornell University College of Veterinary Medicine. Red blood cell inclusions. eclinpath.com/hematology/morphologic-features/red-blood-cells/rbc-inclusions
  7. eClinPath, Cornell University College of Veterinary Medicine. Poikilocytosis. eclinpath.com/hematology/morphologic-features/red-blood-cells/poikilocytosis
  8. Kang MH, Park HM. Hypertension after ingestion of baked garlic (Allium sativum) in a dog. J Vet Med Sci. 2010;72(4):515-518. doi.org/10.1292/jvms.09-0434
  9. Yamato O et al. Heinz body hemolytic anemia with eccentrocytosis from ingestion of Chinese chive (Allium tuberosum) and garlic (Allium sativum) in a dog. J Am Anim Hosp Assoc. 2005;41(1):68-73. doi.org/10.5326/0410068
  10. Yamato O et al. Induction of onion-induced haemolytic anaemia in dogs with sodium n-propylthiosulphate. Vet Rec. 1998;142(9):216-219. doi.org/10.1136/vr.142.9.216
  11. Beleć K et al. The Effect of the Type and Concentration of Garlic (Allium sativum) on Heinz Body Concentrations in Canine Erythrocytes: An In Vitro Study. Animals (Basel). 2025;15(21):3188. doi.org/10.3390/ani15213188

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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