Blood in Dog Stool: What Red or Black Poop Means

Red blood vs black, tarry stool

Vets use two words for blood in stool. Hematochezia means fresh, bright red blood. It usually comes from the lower part of the gut, such as the colon, rectum or anus. You may see red streaks on the surface of the stool, red drops at the end of a bowel movement, or blood mixed with mucus.

Melena means black, sticky, tar-like stool. The black color comes from blood that has been digested on its way through the gut. It usually points to bleeding in the stomach or the upper small intestine. Melena can be easy to miss, because it looks like very dark stool rather than blood.

Some foods, such as liver and other dark meats, can make stool darker than usual. One simple check is to smear a little stool on a white paper towel. Digested blood often looks dark red or black against the white. If you are not sure, take a photo and ask your vet.

Swallowed blood can also turn stool black. A dog with a nosebleed or a bleeding mouth may swallow enough blood to pass dark stool, even when the gut itself is healthy. Your vet will want to know about any bleeding you have seen elsewhere.

Common causes of bright red blood

Fresh blood usually means the colon or the area around the anus is irritated or injured. Common causes include the following.

• Colitis, or inflammation of the colon, often after stress, a diet change or eating garbage
• Intestinal parasites, such as whipworms and hookworms, and single-celled parasites such as Giardia
• Anal gland problems, including impaction and abscesses
• Constipation and hard straining
• Bacterial infections, such as Salmonella
• Food allergies and inflammatory bowel disease
• Rectal polyps and other growths near the anus

Colitis is one of the most common reasons for red blood. Dogs with colitis tend to pass small amounts of soft stool many times a day. They often strain, seem in a hurry to go out, and pass mucus or a little bright red blood near the end. Stress colitis, after boarding, travel or a move, is a frequent cause. Many cases settle quickly with treatment, but the cause still needs to be found. If anal glands may be involved, see our guide to anal gland problems in dogs.

Common causes of black, tarry stool

Black stool suggests bleeding higher up in the gut. It is less common than red blood and is more often linked to serious problems. Possible causes include the following.

• Stomach or intestinal ulcers, often linked to anti-inflammatory medicines, liver disease or some tumors
• Hookworms, which feed on blood in the small intestine
• Swallowed objects that damage the lining of the gut
• Tumors in the stomach or small intestine
• Rat and mouse poisons that stop the blood from clotting
• Other illnesses, such as kidney disease, liver disease and Addison's disease
• Swallowed blood from the nose, mouth or lungs

In dogs, anti-inflammatory pain medicines, cancer and liver disease are among the most common causes of stomach ulcers. Never give your dog human pain relievers unless your vet tells you to. Giving these medicines together with steroids raises the risk of ulcers further.

Serious causes to know about

Parvovirus is a severe viral infection that mainly affects puppies from about 6 weeks to 6 months old, especially those that are unvaccinated or not fully vaccinated. It often starts with tiredness, a poor appetite and fever. Within a day or two, vomiting and diarrhea follow, and the diarrhea is often bloody. About a quarter of dogs with parvovirus have diarrhea without visible blood, so a puppy does not need bloody stool to be at risk. With intensive treatment in hospital, more than 90 percent of dogs survive. Read more in our guide to parvovirus in dogs.

Acute hemorrhagic diarrhea syndrome, once called hemorrhagic gastroenteritis, strikes suddenly in dogs that were healthy the day before. Dogs vomit and pass large amounts of bloody diarrhea that is often described as looking like raspberry jam. Small and toy breeds, such as Yorkshire Terriers and Maltese, are affected most often. These dogs can become dehydrated quickly and need fluids through a drip. With prompt treatment, most recover within a few days.

Anticoagulant rat poisons stop the blood from clotting. Bleeding may show up as red or black stool, nosebleeds, bruising, pale gums or weakness. Signs often appear several days after the poison was eaten, so do not wait for symptoms if you think your dog found bait or a poisoned rodent. Call your vet right away and bring the packaging. For other dangers in the home, see common household poisons.

Hookworms are a particular risk for young puppies. They feed on blood, and a heavy infection can cause dark or bloody stool, pale gums and weakness. Puppies can become seriously anemic even before worm eggs show up in a stool test.

Swallowed objects, such as bone fragments, toys or fabric, can scrape or block the gut. Vomiting, a painful belly and loss of appetite alongside abnormal stool are warning signs. Our guide to swallowed objects in dogs explains what to do.

When it is an emergency

Any blood in your dog's stool is worth a call to your vet. Contact your vet the same day, or an emergency clinic out of hours, if you notice any of these signs.

• Black, tarry stool
• More than a few streaks of blood, or diarrhea that is mostly blood
• Vomiting, especially vomiting that repeats or contains blood
• Weakness, collapse or unusual tiredness
• Pale, white or gray gums
• Refusing food or water
• A painful or swollen belly
• Bruising, nosebleeds or bleeding anywhere else on the body
• Bloody stool in a puppy, or in any dog that is not fully vaccinated
• Any chance your dog ate rat poison, a medicine or a foreign object

If you suspect parvovirus, call the clinic before you arrive. The staff may ask you to wait outside or use a separate entrance, because the virus spreads easily to other dogs.

A single small streak of red blood in an adult dog that is bright, eating and otherwise well is less urgent. It is still sensible to phone your vet for advice. Book a visit if it happens again, lasts more than a day or two, or comes with any other change in your dog.

What to do before you see the vet

Write down when you first saw the blood, how much there was, and whether it was red or black. Note how often your dog is passing stool, whether there is mucus, and whether your dog is straining. Think about any new food, treats, chews, medicines or things your dog may have eaten on walks.

A fresh stool sample in a clean bag or pot is very useful, since it can be tested for parasites and other causes. If you cannot collect a sample, a clear photo helps. Keep fresh water available and do not give any human medicines. Your vet will tell you whether to hold back food.

How vets find the cause

Your vet will ask about the history and examine your dog, checking the gums, hydration, temperature and belly. A rectal exam can find anal gland problems, growths and signs of where the blood is coming from. A stool test looks for worms, Giardia and other parasites. Puppies with bloody diarrhea are often tested for parvovirus.

Blood tests show whether your dog has lost a lot of blood and how well the organs are working. They can also check whether the blood is clotting normally. X-rays or an ultrasound scan may be needed to look for swallowed objects, tumors and other problems. In some dogs, the vet looks inside the stomach or colon with a small camera and takes tiny tissue samples.

Treatment depends on the cause. It may include a bland or special diet, parasite treatment, fluids, medicines to protect the stomach, or surgery to remove a swallowed object. Dogs with severe illness, such as parvovirus or poisoning, often need a stay in hospital.

Prevention

Not every case can be prevented, but a few habits lower the risk. Keep up with vaccinations, including protection against parvovirus. Follow the parasite control plan your vet recommends, and pick up stool promptly. Change food slowly over about a week. Keep garbage, bones, small toys and medicines out of reach, and never give your dog human pain relievers. If you use rat or mouse bait, place it where your dog cannot reach it or the poisoned rodents, or choose another method. For loose stool without blood, see our guide to diarrhea in dogs.

Rescue dogs and blood in stool

Dogs that have lived on the street or in crowded kennels are more likely to carry worms and other parasites. The stress of a move to a new home can also trigger colitis in the first days. At Paw Squadron, every dog we rescue sees a vet and is dewormed. Even so, some parasites are shed on and off and can be missed. If you notice blood in your new dog's stool, a vet visit and a fresh stool test are a sensible first step.

For more practical health guides, browse PawPedia. If you adopted a dog from us and have a question, write to us from the Contact page.