Bloody Stool (Melena and Hematochezia) in Dogs

Key Takeaways

Bloody stool describes the presence of blood in feces and includes digested blood (melena) or undigested blood (hematochezia). 

• Bloody stool is a non-specific symptom triggered by many conditions such as mild, dietary-induced colitis to emergency conditions such as parvovirus infection, hemorrhagic gastroenteritis, or bleeding disorders

• Investigation of blood in the stool involves physical examination, laboratory tests, and diagnostic imaging

• Treatment focuses on the underlying cause and includes medication, surgery, nutritional support, and supportive care 

• Prognosis varies depending on the underlying condition

• Blood in the stools warrants veterinary attention unless it is expected with a previously diagnosed condition

• A first instance of bloody stool warrants urgent veterinary attention

Blood in stool characterized  by sudden onset of passing frequent, small amounts of clotted, red blood or accompanied by symptoms such as pale gums, collapse, or breathing difficulties are an emergency

A Closer Look: What is Bloody Stool in Dogs?

Bloody stool is a common, non-specific symptom associated with many conditions. Many cases are mild and resolve without treatment, whereas other cases indicate a life threatening emergency.  Symptoms and severity of bloody stools vary according to where the blood originated from in the colon and underlying cause. Blood that originates anywhere from the nose/mouth to the small intestine is digested and presents as black, tar-like, foul smelling feces known as melena.

Red blood in the stools is known as hematochezia and originates from the bottom of the small intestine, colon, and rectum. Melena and hematochezia can occur at the same time if bleeding is present in multiple locations.

Underlying causes are numerous and prognosis is similarly varied.

Possible Causes

Bloody stools in dogs are categorized by the type of condition causing the symptoms. Categories and examples of conditions associated with blood in stool include:

Autoimmune disorders such as immune mediated hemolytic anemia, food allergies, and immune mediated thrombocytopenia

Metabolic disorders such as chronic kidney disease (resulting gastric ulceration)

Nutritional disease such as dietary indiscretion

Cancers such as stomach or intestinal cancer, pancreatic cancer, liver cancer, and gastric lymphoma

Infectious diseases such as parvovirus, distemper, campylobacteriosis, and salmonellosis

Parasites such as hookworm and lungworm

Inflammatory disease such as inflammatory bowel disease (IBD)

Diseases of unknown origin (idiopathic) such as hemorrhagic gastroenteritis and antibiotic responsive diarrhea

Poisonings such as NSAID toxicosis, anticoagulant rodenticide toxicosis, blue-green algae toxicosis, sago palm toxicosis, zinc toxicosis, xylitol toxicosis, vitamin D toxicosis, mushroom poisoning , and organophosphate poisoning

And injuries, such as sharp or blunt force injury to the gastrointestinal tract.

Risk Factors

Blood in the stools usually warrants urgent veterinary attention, but cases that present alongside other serious symptoms require emergency veterinary treatment. Emergency symptoms include: 

WeaknessCollapsePale gumsDifficulty breathing • Severe vomiting

• Sudden onset of passing frequent, small, jelly-like clots of blood

Testing and Diagnosis

Investigation of bloody stools includes:

• Physical examination

• Laboratory testing such as fecal analysis, blood tests, and urinalysis

• Antigen test for parvo

• Diagnostic imaging including x-rays, endoscopy, and abdominal ultrasound

Treatment varies depending on the underlying condition. If the condition is known then specific treatment includes medication and surgery. Most cases require symptomatic treatment alongside testing. 

Supportive treatment includes:

• Medication such as gastroprotectants • Fluid therapy • Nutritional support • Blood transfusion in severe cases

Similar symptoms

Sometimes dogs eat something red where the color passes through the gastrointestinal tract. If a dog defecates on printed paper (such as when using newspapers during housetraining) and the ink bleeds, it may be mistaken for blood in stools.

Dogs that have been fed activated charcoal for treatment of toxicosis pass dark black stools.

Associated Symptoms

Other symptoms associated with blood in the stools include:

• Straining to defecate • Pain when defecating • DiarrheaVomiting Weight loss • Loss of appetite

Cases of severe blood loss present with

• Pale gums• Weakness • Collapse

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