Melena (Blood in Stool) in Dogs

Melena is the presence of digested blood in the feces and makes the stools appear black and tarry. Melena is different from fresh blood in the stool (hematochezia). Melena may represent a severe, life-threatening illness, and should not be ignored. It must especially be addressed if it persists or worsens.

Melena develops when bleeding occurs into the stomach or small intestines. The bleeding must be high in the intestinal tract in order for the blood to be digested and become discolored. Bleeding into the colon or rectum (hematochezia) appears as fresh blood in the stool. 

General Causes

Infectious agents

Certain drugs 

Cancer

Foreign bodies in the stomach or intestines

Infiltrative and inflammatory gastrointestinal diseases

Ingestion of blood

Coagulopathies (bleeding disorders)

Metabolic and other diseases that cause gastrointestinal ulceration

Hemorrhagic gastroenteritis (HGE)

Perioperative hemorrhage (bleeding associated with surgery on the intestinal tract)

Gastrointestinal ischemia (lack of blood supply) 

Ingestion of heavy metals (uncommon causes)

What to Watch For

Dark, almost black stools

Diarrhea

Vomiting

Pale gums

Other areas of bleeding or bruising on the body

Weight loss

Poor appetite

Excessive drinking or urinating

Excessive urinating

Diagnosis

A thorough history and physical examination are often helpful in determining if melena is present and in suggesting an underlying cause. To determine the exact cause, additional tests are usually necessary and include the following:

Complete blood count (CBC)

Biochemical profile

Urinalysis 

Fecal examination

Abdominal and chest radiographs (X-rays) 

Serology for certain infectious diseases

Coagulation profile

Abdominal ultrasonography

Upper gastrointestinal barium series

Endoscopy