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.

Guerra.jpgDr. 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?