Skip to main navigation Skip to main content

Animal Health Foundation Animal Health Foundation
Dog with tongue out

Bloody Diarrhea in Dogs

Dr. Beth Guerra, an emergency veterinarian at Animal Critical Care and Emergency Services (ACCES) hospital in Renton, answers this week's questions about bloody diarrhea. It is the first of a two-part series.

Question: What causes bloody diarrhea in dogs?

Answer: Bloody stool or diarrhea is common in veterinary medicine and often constitutes an emergency because it is so alarming. Blood can show up in the stool in two ways -- as hematochezia, which is the presence of bright red blood with normal feces or diarrhea, or as melena, which is digested blood that often gives the stool a dark, tarry appearance.

Question: What is the difference (aside from the way they look)?

Answer: Dark, tarry melena represents blood that has come from the upper GI tract, such as the stomach or first part of the small bowel. It essentially has been "digested" as it moves through the intestine and, therefore, appears dark and sticky.

Conversely, bright red hematochezia represents blood from the descending colon, rectum, or anus, and appears more like actual blood.

Question: What can cause the bright red bleeding in hematochezia?

Answer: There are myriad causes that can span all ages and breeds. A thorough history and physical exam should always be performed on any patient that has hematochezia. It is also important to determine if the stool has been normal or if the pet has been having diarrhea.

External causes include masses or abscesses around the anus or anal glands that are brittle or have ruptured, trauma, passing of a foreign body, hernias or fistulas. Internal causes include colitis, stress, constipation, certain infectious organisms such as campylobacter or clostridium, parasites, masses or polyps, a prolapsed rectum or blood-clotting problems.

Question: What causes the dark, sticky bleeding in melena?

Answer: Melena is caused by any bleeding in the esophagus, stomach, or first part of the small intestine. It also can represent blood from the oral cavity, nasal cavity or lung that has been swallowed.

The stool appears dark and tarry and can have a foul odor. If vomiting occurs, it often resembles "coffee grounds."

Melena can be caused by direct bleeding in the GI tract from ulcerations in the esophagus, stomach or beginning part of the intestine, parasites, trauma from passing foreign bodies, inflammatory bowel disease, or intestinal or stomach cancer.

Systemic disease such as liver failure, blood-clotting problems, kidney failure, Addison's disease, pancreatitis, certain types of cancer (such as mast cell tumor) or shock situations (such as severe heat stroke) can also lead to bleeding in the bowel.

Wounds in the oral cavity, nasal bleeding or pulmonary hemorrhage, where blood is coughed up and swallowed, can also cause melena.

Question: What are the most common symptoms of hematochezia?

Answer: Usually blood mixed with normal stool or diarrhea. The pet is often straining to defecate and may be passing small amounts of stool with bright red blood or large amounts of bloody fluid. Often blood can be seen around the perineal area or on the fur or is detected on rectal exam by the veterinarian.

Because these causes are localized, patients rarely exhibit systemic disease.

Weight loss, lethargy and vomiting are usually not observed; however, there is a disease process associated with hematochezia that can be quite severe, known as hemorrhagic gastroenteritis (HGE). This is characterized by acute onset of bloody diarrhea, often accompanied by vomiting, and signifies acute inflammation within the GI tract. Patients with HGE are quite ill and usually require hospitalization.

Question: What are the most common symptoms of melena?

Answer: Melena may be more subtle and difficult for owners to detect because it is not as conspicuous as bright red blood.

Diagnosis is usually made by rectal exam or examination of the feces by a veterinarian. Patients are usually ill and may exhibit a variety of symptoms including weight loss, lethargy, lack of appetite, pale gums or weakness that indicates anemia, or a history of coughing or respiratory difficulty.

Question: How is hematochezia diagnosed and treated?

Answer: Your vet should examine the anus, anal glands and rectum to rule out the possibility of a mass, polyp, or abscess.

A fecal examination is needed to rule out intestinal parasites.

If the bleeding does not diminish with treatment or the pet is critically ill (as in HGE), further diagnostics, such as a CBC/chemistry, abdominal ultrasound, or colonoscopy, should be considered.

Treatments are varied and depend on the diagnosis.

Question: How is melena diagnosed and treated?

Answer: Melena is usually an indication of a more serious illness, and because it indicates bleeding from higher up in the GI tract, more thorough diagnostics are often required initially.

The owner should be questioned about possible trauma, exposure to toxins such as rat baits that interfere with clotting (D-Con), or drugs such as NSAIDs or steroids.

Generally, a diagnostics workup should include a CBC/chemistry, urinalysis, fecal exam and coagulation profile.

Abdominal ultrasound and endoscopy can often be used to augment these initial diagnostics and are most useful in evaluating the GI tract.

Again, treatment is varied and depends on the source of the bleeding.

Question: When do I need to take my pet to the vet?

Answer: In general, any change in appearance, frequency or volume of feces can indicate a medical problem. The presence of blood in the feces, in any form, warrants a physical exam by a veterinarian.

Further diagnostics and treatment can be discussed at that time based on the history of the patient and the results of the exam.

Prognosis can be excellent, in the case of hematochezia caused by parasites, or guarded, as when melena is caused by GI ulceration or cancer.

Dr. Beth Guerra

Guerra is a graduate of the veterinary college at the University of Illinois in 2001. She worked in day practice in Chicago before moving to Seattle in 2003. She joined the ACCES staff in 2007 and works in the Renton hospital. Guerra enjoys treating trauma patients and exotic animals.

Return to news and events