Blood in Dog Poop: What It Means and What to Do

Blood in your dog’s poop is one of those findings that sends owners straight to their phones, and it is right to take it seriously. But "blood in the stool" covers a wide range (from a single bright red streak after a stressful kennel stay to a life-threatening illness) and the colour, amount and consistency tell you a great deal about which you are dealing with.

This article explains how to read what you are seeing, the common causes, what to do at home and when to go to a vet.

Bright red or black? The two kinds of blood

Bright red blood (vets call it hematochezia) has not been digested, which means it comes from the lower part of the digestive tract: the colon, rectum or anus. It may appear as streaks on the outside of a formed stool, drops at the end of a bowel movement, or blood mixed through soft, mucus-covered diarrhea.

Black, tarry stool (melena) is blood that has passed through the digestive tract and been partly digested on the way, so it comes from higher up: the stomach or small intestine. It looks dark, sticky and shiny, a little like tar, and often smells unusually bad. Melena is less common than red blood but more often a sign of something significant, such as a bleeding stomach ulcer, so it always warrants a vet visit the same day.

A useful check: if you dab a dark stool onto white kitchen paper, digested blood often leaves a reddish-brown tinge.

Common causes of bright red blood

• Colitis. Inflammation of the large intestine is the most common cause of bright red blood. It usually brings frequent, urgent, small amounts of soft stool with mucus, sometimes with straining. Triggers include eating something unsuitable, a sudden diet change, stress, parasites and infections.
• Dietary indiscretion. Rubbish, bones, sticks and rich food can scrape or irritate the bowel.
• Parasites such as whipworms, hookworms, Giardia and coccidia, especially in puppies and young dogs.
• Anal gland problems and other irritation around the bottom, which can leave a little blood on the stool or where your dog has been sitting.
• Constipation and straining, where a hard stool damages the lining on the way out.
• Acute hemorrhagic diarrhea syndrome (AHDS), described below, an emergency.
• Less commonly, polyps or tumours of the rectum, and bleeding disorders.

Blood with mucus

A slimy, jelly-like coating on the stool is mucus, which the lining of the large intestine produces to protect itself. A little mucus with a streak of fresh blood, often in soft stool passed urgently and frequently, is the typical picture of colitis. It is common after stress, a diet change or scavenging and often settles within a few days with a simple diet, but it should be checked if it continues, recurs or your dog seems unwell.

Causes of black, tarry stool

• Stomach or intestinal ulcers, which are a well-known side effect of anti-inflammatory painkillers. Human medicines such as ibuprofen and naproxen are particularly dangerous for dogs.
• Swallowed blood, for example from a nosebleed or a mouth injury.
• Bleeding disorders, including poisoning with anticoagulant rat and mouse baits, which stop blood from clotting.
• Tumours of the stomach or small intestine, mainly in older dogs.
• Severe illness elsewhere, such as liver or kidney disease.

The emergency: AHDS (formerly HGE)

Acute hemorrhagic diarrhea syndrome comes on suddenly, often in a dog that was perfectly well the day before. Affected dogs produce large amounts of bloody, jelly-like diarrhea (often described as looking like raspberry jam) and frequently vomit as well. They lose fluid very quickly and can go into shock.

The condition is thought to be linked to toxins from Clostridium perfringens bacteria damaging the lining of the intestine. It is seen most often in small and toy breeds. With prompt treatment, mainly intravenous fluids and supportive care, most dogs recover well within a few days, but delays are dangerous. If your dog has this kind of diarrhea, go to a vet straight away.

Bloody diarrhea in a young puppy should also be seen urgently, because parvovirus causes similar signs and is often fatal without treatment.

When to call the vet

What you can do at home

If your dog has a little bright red blood on its stool and is otherwise bright, eating and drinking:

1. Take a photo of the stool, or bag a sample in case your vet wants to test it for parasites.
2. Keep the diet simple. Avoid treats, table scraps and anything new. Some vets suggest a short course of a bland, low-fat diet or a veterinary gastrointestinal food.
3. Make sure fresh water is always available, and watch that your dog is drinking.
4. Monitor closely for more blood, diarrhea, vomiting, lethargy or loss of appetite over the next 24 hours.

Do not give human anti-diarrhea medicines or painkillers. Some contain ingredients that are harmful to dogs, and stopping diarrhea can mask a problem that needs treatment.

What the vet will do

Your vet will ask about the colour and amount of blood, the stool consistency, your dog’s diet, possible scavenging, medicines and vaccination history, and will examine your dog, often including a rectal examination. Common next steps are a stool test for parasites and infections, blood tests to check for blood loss, dehydration and clotting problems, and sometimes X-rays, ultrasound or endoscopy.

Treatment depends on the cause. Simple colitis is often treated with a temporary diet change and, where needed, medicines, parasites with a dewormer, and AHDS with hospital care and fluids. If vomiting is part of the picture, read dog throwing up: causes and when to worry, and if there is any chance your dog ate a poison, see dog poisoning and first steps.