What this means
Blood in stools looks different depending on where it came from, and the difference matters. Bright red, unchanged blood usually comes from the large intestine or the rectum, close enough to the exit that digestion has not altered it. Black, shiny, tar-like stools mean the blood was digested on the way through, so the bleeding was higher up, in the stomach or small intestine. That second picture is the more serious sign, even when the amount looks small.
Quantity matters too. A few streaks in mucus after hard straining is a different thing from a pool of liquid blood. Neither, though, is something to simply watch for a few days — even small bleeding that repeats needs an explanation.
Photograph the stool and, if you can, keep a sample. That tells your vet more than any description, and by the time of the appointment it may look quite different.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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Severe irritation of the large intestine
An inflamed large-intestine lining bleeds readily. The pattern is small amounts of stool with mucus and bright red streaks, passed with straining and more often than usual.
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A gut infection or parasites
Some organisms damage the gut lining and cause bloody diarrhoea. Young dogs cope with it worse because they lose fluid faster.
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Inflammation of the pancreas
A more severe pancreatic inflammation can show as bloody diarrhoea alongside vomiting, belly pain and lethargy. This is not something to watch at home.
About the condition: Pancreatitis -
A foreign object, or something sharp that was swallowed
A bone splinter or another sharp object can damage the gut wall. Vomiting and a painful belly usually go with it.
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Problems with blood clotting
When clotting is disturbed, bleeding in the gut can start with no obvious injury. You may also notice bruising on the skin or bleeding from the nose.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Whether the blood is bright red, or the stools are black and tarry
- How much blood there is, and whether it is repeating
- Whether your dog is vomiting too
- Whether the gums look pale
- Whether your dog is bright, or flat and reluctant to get up
- Whether there is any bruising on the skin
When to book a routine visit
Even a single small amount of blood in the stool is a reason to contact your vet the same day and agree how quickly to come in. If there is a lot of blood, if the stools are black, or if your dog is flat with pale gums, go straight away.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Inflammatory bowel disease (IBD) Digestion and liver This is a long-term disorder of the digestive tract in which inflammatory cells build up in the wall of the stomach or intestine, so it becomes less able to digest food and absorb nutrients. The exact cause is not fully understood; an interplay between the immune system, gut bacteria and food is thought to play a part. Because many other digestive problems look much the same, a vet works out what is really going on with tests.
- Pancreatitis Digestion and liver Pancreatitis is inflammation of the pancreas, in which digestive enzymes become active too early and start to irritate the pancreas itself and the tissue around it. It can come on suddenly or smoulder for a long time with repeated flare-ups, and in more severe cases it affects other organs too. The causes vary, so working out what is going on with a particular dog is a job for the vet.
- Protein-losing enteropathy Digestion and liver This is a condition in which a damaged gut wall lets too much protein from the blood leak into the intestine, where it is lost. It is not a single disease but the result of various intestinal disorders, such as long-term inflammation or changes in the gut's lymph vessels. When protein levels in the blood fall, fluid can collect in the belly or under the skin, so this is a condition that needs a vet's attention.
- Cancer Cancer Cancer is not one disease but a whole group of different malignant tumours that can appear in almost any organ or tissue. They can grow slowly or quickly and spread to other parts of the body, so the earlier a change is noticed, the more options a vet has. Only a vet can tell whether a lump or other change is malignant.
- Thrombocytopathy Blood and immunity Thrombocytopathy is a blood clotting disorder in which the blood has enough platelets but they do not work as they should, so bleeding is slow to stop. It can be inherited or arise from another illness or certain drugs. In such a dog even a small wound or a veterinary procedure can lead to prolonged bleeding, so it is worth telling the vet about it beforehand.
- Parvovirus Infections Parvovirus is a highly contagious viral disease of dogs that damages the lining of the gut and the blood cells that defend the body against infection. Puppies and unvaccinated dogs are at greatest risk. The illness moves fast and the dog loses a great deal of fluid, so it needs a vet immediately.
Body systems: Digestion and liver Cancer Blood and immunity Infections