Blood in Dog Stool: Causes, When to Worry and What to Do

What it usually means

Blood in stool shows up in two main ways. Bright red blood (hematochezia) is fresh and usually comes from the lower digestive tract: the colon, rectum or anus. You may see streaks on a firm stool, or blood and mucus with loose stool. Black, tarry stool (melena) is digested blood, usually from higher up, in the stomach or small intestine.

Not everything that looks bloody is. Beets and red-dyed treats can tint stool red, and diets high in organ meats or dark proteins can darken it. If you are unsure, wipe the stool with a paper towel and see whether the smear looks dark red or black.

Causes range from minor to life-threatening. Eating something unsuitable, colitis, worms and anal gland problems are common. Serious causes include parvovirus, acute hemorrhagic diarrhea syndrome, blockages, ulcers, clotting disorders and tumors. You cannot tell them apart by looking, which is why vets advise a call whenever a dog passes blood. If the stool is loose as well, our page on diarrhea covers the general picture.

Common causes

Cause	What it means	Urgency
Dietary indiscretion	Spoiled food, sticks, bones, new treats or chews, or an abrupt diet change can irritate the gut and cause bleeding.	Call your vet
Colitis	Inflammation of the large intestine. Typically frequent, small, loose stools with straining, mucus and sometimes fresh blood.	Call your vet
Intestinal parasites	Hookworms, whipworms, coccidia and giardia can all cause bloody stool.	Call your vet
Anal gland problems	Infected or blocked anal sacs can cause bleeding and discomfort near the rear.	Call your vet
Acute hemorrhagic diarrhea syndrome	Formerly called hemorrhagic gastroenteritis (HGE). Sudden vomiting and profuse bloody diarrhea that can lead to shock without prompt fluids.	See a vet now
Parvovirus and other infections	Parvovirus, salmonella and other infections can cause bloody diarrhea. Parvovirus is especially dangerous in puppies and unvaccinated dogs.	See a vet now
Foreign object or intussusception	A swallowed object or a telescoping bowel can cause bloody stool, often with vomiting or belly pain.	See a vet now
Ulcers and drug reactions	Stomach or intestinal ulcers can cause black, tarry stool. Some pain relievers and steroids can trigger them.	See a vet now
Clotting problems and rat poison	Anything that stops blood from clotting properly can cause bleeding in the gut.	See a vet now
Inflammatory bowel disease, tumors and other serious illness	Chronic gut disease, pancreatitis and cancer can all show up as blood in the stool.	Call your vet

What you can do at home

Do not try to treat blood in the stool on your own. Call your vet, describe what you see, and ask whether your dog needs to be seen right away. A phone call can help sort out how urgent it is. If your dog is unvaccinated, young or may have parvovirus, call ahead before visiting a clinic or emergency hospital.

While you wait, keep fresh water available. Make notes your vet will want: the color, consistency, amount and frequency of the stool, when the blood first appeared, any recent changes in food, treats or chews, anything your dog could have eaten, and other symptoms. Collect a fresh stool sample in a clean container or bag to take with you.

Ask your vet before offering food, even a bland meal. Do not give any human medicine. Never give your dog human pain medicines such as ibuprofen, aspirin or acetaminophen on your own. Ibuprofen and aspirin can cause stomach ulcers and bleeding in dogs, and acetaminophen can damage the liver. If your dog takes a prescribed medicine, tell your vet and ask whether to give the next dose.

If you think your dog ate rat poison or another toxin, call your vet or an emergency clinic, or in the US ASPCA Animal Poison Control at (888) 426-4435 or Pet Poison Helpline at (855) 764-7661 (fees may apply).

What happens at the vet

Your vet will ask about the stool, your dog's diet, vaccines and parasite prevention, and any chance of eating something harmful. A physical exam includes feeling the belly and a rectal exam, which checks for masses, foreign material and anal gland problems.

Tests depend on what the exam suggests. A fecal exam looks for parasites and bacteria. Puppies and unvaccinated dogs are usually tested for parvovirus. Bloodwork shows blood loss, dehydration, organ function and clotting, and X-rays or ultrasound can find blockages, thickened bowel walls or tumors. Sometimes endoscopy or colonoscopy with biopsies is needed.

Treatment follows the cause. Many dogs need fluids to fix dehydration and mineral loss, and severe cases need hospital care. Parasites are treated with antiparasitic medicine, diet is adjusted, and surgery is needed for some blockages, tumors or other problems. Most dogs with acute hemorrhagic diarrhea syndrome recover well when treated promptly with fluids. Some dogs improve within a day or two, while others stay in the hospital for several days.

Prevention

Keep vaccinations current, especially against parvovirus, and use year-round parasite prevention as your vet advises. These steps help protect against parvovirus and intestinal parasites, two common causes of bloody stool.

Avoid abrupt diet changes. Introduce new foods, treats and chews gradually, and skip table scraps. Keep garbage secured, and store toxins, rat poison and medicines where your dog cannot reach them. If your dog eats non-food items, supervise outings and use a gate or crate when you cannot watch.

Never give human pain medicines on your own. Drugs such as ibuprofen and aspirin can cause stomach ulcers and bleeding in dogs.

Minimize stress where you can, since stress can bring on colitis and bloody stool in some dogs.

Frequently asked questions

Is a little blood in my dog's stool an emergency?

Not always, but call your vet whenever you see blood. A few streaks of bright red blood in a stool, in a dog who is bright and eating, may be minor, and a quick phone call can help decide how urgent it is. Go straight in for black stool, large amounts of blood, vomiting, weakness or pale gums.

What does black, tarry stool mean in a dog?

It usually means digested blood from the stomach or small intestine, possibly from an ulcer or a drug reaction. It is a red flag and needs a vet visit right away. Some foods can darken stool, so wipe it on a paper towel to check whether it looks black.

Why does my dog have bloody diarrhea but still acts normal?

Even a dog who seems fine can have a problem that gets worse, so get an exam. Dehydration can build quickly, especially in puppies and small dogs, and some causes such as parvovirus are dangerous.

Can stress cause blood in dog stool?

Stress can trigger colitis, which can cause loose stool with mucus and sometimes blood. But do not assume stress is the cause. A vet should rule out parasites, infections and other problems.

What should I bring to the vet?

A fresh stool sample in a clean container, a list of your dog's food, treats, chews and medicines, and notes on when the blood first appeared and any other symptoms.

Written from veterinary sources by the Pawsplained editorial team. Not yet reviewed by a veterinarian; this is general information, not a diagnosis or treatment plan. Updated Oct 30, 2026. Editorial policy