Bloody Diarrhea in Dogs: Causes, HGE and When It's an Emergency

Red Blood vs. Black Stool: What It Means

• Bright red blood (hematochezia): fresh blood that usually comes from the large intestine or rectum. It often comes with mucus, straining and frequent, urgent small stools, a pattern typical of colitis.^7,8
• Black, tarry stool (melena): digested blood from higher up, such as the stomach or small intestine, and occasionally from swallowed blood. Black stool always needs a vet.^2,9
• "Raspberry jam" diarrhea: large amounts of bloody, jelly-like diarrhea that starts suddenly is typical of AHDS.^3,4

Note that Pepto-Bismol turns stool black, which can look like or mask bleeding, so don't give it unless your vet tells you to.^10,11

Causes of Bloody Diarrhea in Dogs

• Colitis: inflammation of the large intestine, from causes such as dietary indiscretion, stress, parasites or inflammatory bowel disease^8,2
• Acute hemorrhagic diarrhea syndrome (AHDS), formerly called hemorrhagic gastroenteritis (HGE)³
• Parvovirus, especially in puppies and unvaccinated dogs^5,6
• Parasites: whipworms can cause fresh blood in the stool, threadworms can cause blood-streaked diarrhea, and severe hookworm infections cause dark, tarry diarrhea and anemia in puppies¹²
• Swallowed objects, toxins (including rat poison), ulcers, tumors and infections^2,13

Acute Hemorrhagic Diarrhea Syndrome (HGE)

AHDS causes sudden vomiting and profuse bloody diarrhea, often described as looking like raspberry jam, in dogs that were healthy just before.^3,4 It's most common in young to middle-aged small and toy breeds such as Yorkshire Terriers, Miniature Pinschers, Miniature Schnauzers, Miniature Poodles and Maltese.³ The exact cause isn't known, but toxins from the bacterium Clostridium perfringens are thought to be involved. It isn't considered contagious.^3,4

• Why it's an emergency: dogs can lose fluid so fast that they go into shock before they look dehydrated.³
• Treatment: prompt IV fluids are the main treatment, along with anti-nausea medicine and supportive care. Antibiotics are no longer routinely used unless a dog is severely ill or shows signs of sepsis.^3,4,14
• Outlook: with prompt treatment the prognosis is good, and fewer than 10% of hospitalized dogs die. Most recover within a few days.^3,4

My Dog Has Bloody Diarrhea but Is Acting Normal

A small streak of red blood in soft stool from a dog that is bright, eating and drinking is often caused by mild colitis, but you should still call your vet the same day.^1,2 Dogs with AHDS can go downhill within hours, so watch closely and go to a vet right away if the diarrhea becomes larger in volume or jam-like, or your dog starts vomiting or seems tired.³

What Will a Vet Do for Bloody Diarrhea?

Your vet will examine your dog and check for dehydration. Tests may include a stool test for parasites, a parvovirus test, bloodwork (a very high red-cell concentration is a clue to AHDS) and X-rays or ultrasound.^2,5,4 Treatment depends on the cause and may include:

• Fluids: IV fluids for dehydrated dogs. A study found that some dogs with mild to moderate dehydration from bloody diarrhea could be rehydrated with an oral electrolyte solution in the hospital.^3,15
• Anti-nausea medicine and a bland, easily digested diet^3,8
• Dewormers if parasites are found²
• Antibiotics only for severe cases: current guidelines recommend against them for mild or moderate bloody diarrhea, because they don't speed recovery.¹⁶

See dog diarrhea treatment for more on medicines.

Frequently Asked Questions

Is bloody diarrhea in dogs an emergency?

It can be. Go to a vet right away if there's a lot of blood, the diarrhea looks like raspberry jam, or your dog is vomiting, lethargic or a puppy. A few streaks of blood in a dog that seems well still warrant a call to your vet the same day.

Will bloody diarrhea go away on its own?

Mild bloody diarrhea from colitis sometimes settles within a few days, but serious causes such as AHDS and parvovirus can become life-threatening quickly. Have your vet check your dog rather than waiting.

What can I give my dog for bloody diarrhea?

Don't give home medicines. Keep water available and call your vet, who can find the cause and treat it. Pepto-Bismol can turn stool black and hide bleeding.

Why does my dog's poop look like jelly with blood in it?

Jelly-like stool usually contains mucus from an inflamed large intestine (colitis). Large amounts of bloody, jam-like diarrhea can be a sign of acute hemorrhagic diarrhea syndrome, which needs urgent care.

Can a dog survive hemorrhagic gastroenteritis?

Yes. With prompt treatment, mainly IV fluids, the outlook is good and most dogs recover within a few days. Without treatment it can be fatal.

Do dogs with bloody diarrhea need antibiotics?

Usually not. Current guidelines reserve antibiotics for dogs that are severely ill, show signs of sepsis or have certain blood-test changes, which includes most dogs with parvovirus. They don't help mild or moderate cases recover faster.