HGE in dogs looks like this: a dog that was fine this morning starts vomiting, then passes sudden, bloody diarrhea that often looks like raspberry jam, and goes quiet and flat. Its newer name is acute hemorrhagic diarrhea syndrome (AHDS).
Dogs with HGE lose fluid into the gut very fast and can slide into shock before they even look dehydrated. If you see bloody diarrhea with vomiting, call your vet or the nearest emergency clinic now. With prompt treatment, most dogs clearly improve within the first 48 hours.
Symptoms of HGE in Dogs
The signs come on suddenly, usually in a dog that was healthy the day before and had nothing unusual in its history. Look for:
- Bloody diarrhea: large amounts, sudden, often red and jelly-like. The Merck Veterinary Manual notes it is often said to resemble raspberry jam.
- Vomiting, which often starts first. In a study of 108 dogs with AHDS, vomiting came before the bloody diarrhea in 80% of them, and about half of those vomited blood.
- Lethargy: the dog is dull, weak or just lies there.
- Not eating.
- Belly pain.
Which Dogs Get HGE?
Any dog can, but small and toy breeds and young adult dogs are overrepresented. The breeds named most often are the Yorkshire Terrier, Miniature Pinscher, Miniature Schnauzer, Miniature Poodle and Maltese. In the 108-dog study, the typical patient weighed about 10 kg (22 lb) and was 5 years old, and cases were more common in winter.
When to Call the Vet: Right Now
Bloody diarrhea with vomiting is not a "wait until tomorrow" problem. In AHDS, fluid, protein and red blood cells leak from the damaged intestine into the gut. A dog can lose so much fluid so fast that it goes into shock before the usual dehydration signs show. A normal-looking skin pinch does not mean your dog is fine.
Go to a vet or an emergency clinic immediately if your dog has bloody diarrhea and any of these:
- Repeated vomiting, or vomiting blood
- Weakness, collapse or not getting up
- Pale gums, a racing heartbeat or weak pulses (signs of shock)
- Refusing food and water
- It's a small dog, a young puppy or a dog that isn't fully vaccinated
If you're unsure, call anyway and let the clinic decide. Our guide to signs of dehydration in dogs explains what vets check, but with HGE don't wait for those signs to appear.
What to Do While You Get Help
- Call ahead so the clinic is ready for you. After hours, go to your nearest 24/7 emergency hospital.
- Note the timeline: when the vomiting and diarrhea started and how many times each has happened.
- Take a photo of the stool and any vomit. It shows the vet what you saw.
- Keep your dog away from other dogs until your vet has ruled out parvovirus. Parvo looks similar, spreads through stool and is highly contagious, so vets isolate suspected cases.
- Don't give human medicines or home remedies. Your dog needs fluids into a vein, which only a vet can give.
What Is HGE (AHDS)?
Acute hemorrhagic diarrhea syndrome is a sudden, severe bloody diarrhea, often with vomiting, that can cause serious and sometimes life-threatening dehydration. Researchers call it one of the most common causes of sudden bloody diarrhea in dogs.
The damaged gut lining becomes leaky. Water, protein and red blood cells pour into the intestine and out as diarrhea. Because the dog loses more water than red blood cells, its blood becomes thick and concentrated. Vets call this hemoconcentration, and it is the clue that points them toward AHDS.
Why the Name Changed From HGE to AHDS
"Gastroenteritis" means inflammation of the stomach and intestines. When researchers took biopsies from dogs with the condition, they found the damage in the intestines, not in the stomach, and proposed the name acute hemorrhagic diarrhea syndrome. Merck now lists it under AHDS. You'll still hear both names, and they mean the same thing.
What Causes HGE in Dogs?
The exact cause isn't proven, but the evidence keeps pointing at one bacterium, Clostridium perfringens, and the toxins some strains make:
- C. perfringens was found on the lining of the small intestine in every dog in one biopsy study.
- Another study found strains carrying a pore-forming toxin gene called netF in the damaged intestines, and the authors suggested this toxin causes much of the tissue damage.
- In stool samples, these toxin genes turned up in 48% of dogs with AHDS, 12% of healthy dogs and none of the dogs with parvo.
That is a strong link, not yet proof of cause. Most affected dogs have nothing unusual in their history, and there is no proven way to prevent AHDS.
HGE vs Parvo: How to Tell the Difference
Both cause sudden vomiting and bloody diarrhea, so owners often mix them up. Your vet will treat it as possible parvo, too, until a test settles it.
HGE (AHDS) | Parvovirus | |
|---|---|---|
Typical dog | Small or toy breed, young adult (often around 5 years) | Puppy 6 weeks to 6 months, unvaccinated or not fully vaccinated |
Contagious? | Not considered contagious | Highly contagious; the virus survives in the environment for months |
Early signs | Vomiting, then sudden bloody diarrhea | Lethargy, not eating, fever, then vomiting and bloody diarrhea |
Blood test | Very concentrated blood (high PCV) | Low white blood cell count in most dogs |
Stool test | Parvo test negative | Positive parvo antigen test |
Prevention | None proven | Vaccination |
A low white blood cell count in a dog with bloody diarrhea makes vets think of parvo or a bloodstream infection, so they test for parvo straight away. Vaccination is the best protection against parvo; see our guide to the DHPP vaccine.
How Vets Diagnose HGE
AHDS is still a diagnosis of exclusion: the vet confirms the typical picture and rules out other causes of bloody diarrhea. Expect:
- Packed cell volume (PCV) and total protein. This quick blood test shows how concentrated the blood is, and in AHDS a very high PCV, often above 60%, is typical, while total protein stays normal or a bit low.
- Bloodwork for blood sugar and electrolytes. Potassium, sodium and chloride can drop, and blood sugar can be low (see low blood sugar in dogs).
- A parvo test and stool tests for parasites such as hookworms and whipworms.
- X-rays or ultrasound to check the belly for other problems.
Other conditions that can cause bloody diarrhea include parvovirus and other infections, intestinal parasites, Addison's disease (hypoadrenocorticism), clotting problems such as rat poison, stomach or intestinal ulcers, pancreatitis, tumors and a tear in the gut. Our dog poop color chart explains what different stool colors can mean.
How HGE Is Treated
Treatment is about replacing what the gut is losing, fast:
- IV fluids are the main treatment. They restore blood volume, thin the blood and correct electrolytes. Most dogs are hospitalized for this.
- Anti-nausea medicine such as Cerenia or ondansetron, chosen and dosed by your vet.
- Plasma or other colloids for dogs whose blood protein drops very low or who are in shock.
- Glucose and potassium added to the fluids when bloodwork shows they are low.
- A feeding plan from your vet, who will tell you when and what to feed. Follow it rather than a schedule from the internet.
Does My Dog Need Antibiotics?
Usually not. Most dogs recover with fluids and supportive care alone. Antibiotics are kept for dogs with signs of sepsis (bacteria in the bloodstream), such as a dog that stays very sick despite fluids or has a very low white blood cell count. Your vet decides.
This is a real shift from older HGE advice, and it rests on good evidence:
- In a blinded trial, dogs with HGE and no signs of sepsis did just as well on a placebo as on an antibiotic: no difference in deaths, hospital stay or severity.
- Of 237 hospitalized dogs, 62% got no antibiotics and 96% survived to go home.
- A 2024 systematic review found high-certainty evidence that antibiotics make no clinically relevant difference in mild or moderate acute diarrhea in dogs.
So if your vet skips them, that follows the current evidence. Our metronidazole guide explains why vets now use antibiotics less for diarrhea in general.
How Long Does HGE Last? Recovery and Outlook
Most dogs turn the corner fast once fluids start. In the 108-dog study, the clear improvement came within the first 48 hours.
The outlook is good with prompt treatment. Merck puts deaths at under 10% in hospitalized dogs, and in the 237-dog study 96% survived to discharge. Without treatment the risk is much higher. Serious complications include shock, very low blood protein, sepsis and a clotting disorder called DIC.
Some dogs have gut trouble long after the episode. In a follow-up of dogs that had an episode of acute bloody diarrhea, 28% later showed signs of chronic gut disease, compared with 13% of similar dogs that never had it. If your dog has ongoing tummy trouble months later, mention the HGE episode to your vet.
Is HGE Contagious?
AHDS itself is not considered contagious. The catch is that parvo looks similar and is highly contagious, so keep a sick dog away from other dogs until your vet has ruled it out.
Is Bloody Diarrhea in Dogs an Emergency?
Yes. Sudden bloody diarrhea, especially with vomiting or lethargy, needs a vet straight away. Cornell's Riney Canine Health Center lists blood with vomiting or diarrhea, and lethargy or refusing food alongside them, as warning signs. AHDS can kill if it isn't treated, and dogs can go into shock before they look dehydrated.
Why Is My Dog Not Eating After HGE?
A sore, healing gut, leftover nausea and the stress of a hospital stay can all dull a dog's appetite for a while. Follow the feeding plan your vet sends home with you. If your dog won't eat, starts vomiting again or the diarrhea returns, call your vet.
Questions to Ask Your Vet
- Is this HGE (AHDS), or could it be parvo or something else? Which tests rule those out?
- How concentrated was my dog's blood, and how will you know when it's back to normal?
- Does my dog need antibiotics, and if so, why?
- What should I feed at home, and when?
- Which signs mean I should bring my dog straight back?
Originally written by Dr. Kaylee Ferreira. Updated by the I Love Veterinary editorial team.
Sources
- Merck Veterinary Manual: Acute Hemorrhagic Diarrhea Syndrome in Dogs
- Merck Veterinary Manual: Canine Parvovirus Infection
- Merck Veterinary Manual: Evaluation and Initial Treatment of Dog and Cat Emergencies
- Cornell Riney Canine Health Center: When to Go to the ER
- Unterer and Busch 2021, Vet Clin North Am Small Anim Pract: Acute Hemorrhagic Diarrhea Syndrome in Dogs
- Unterer et al. 2014, J Vet Intern Med: Lesions and bacterial invasion in dogs with AHDS
- Leipig-Rudolph et al. 2018, J Vet Diagn Invest: Intestinal lesions and netF-positive Clostridium perfringens
- Sindern et al. 2019, J Vet Intern Med: netE and netF toxin genes in dogs with AHDS
- Mortier et al. 2015, Vet Rec: Acute haemorrhagic diarrhoea syndrome in dogs, 108 cases
- Unterer et al. 2011, J Vet Intern Med: Amoxicillin/clavulanic acid vs placebo in dogs with HGE
- Dupont et al. 2021, J Vet Intern Med: 237 dogs hospitalized with suspected AHDS
- Scahill et al. 2024, Vet J: Antimicrobial and nutraceutical treatment for canine acute diarrhoea (ENOVAT systematic review)
- Skotnitzki et al. 2022, J Vet Intern Med: Chronic gastrointestinal signs after acute hemorrhagic diarrhea
This article is for general information and is not a substitute for advice from your veterinarian.
