Why Is There Blood in My Dog's Stool?

Blood in a dog's stool understandably causes panic, but the type of blood matters enormously for determining urgency.

Hematochezia — bright red blood on the surface of formed stool or mixed with soft stool — typically comes from the lower digestive tract (colon, rectum, or anus). Common causes include colitis (inflammation of the colon from stress, dietary indiscretion, or infection), anal gland issues, intestinal parasites, and minor rectal trauma from straining. While it looks alarming, a small amount of bright red blood on otherwise normal stool in a dog who is acting well is often not an emergency.

Melena — dark, black, tarry stool — indicates digested blood from higher in the GI tract (stomach or small intestine). This is generally more concerning because it can indicate stomach ulcers, internal bleeding, or ingestion of something caustic. Melena always warrants prompt veterinary evaluation.

Hemorrhagic gastroenteritis (HGE/AHDS) causes dramatic, sudden-onset bloody diarrhea that looks like raspberry jam. It comes on rapidly and can cause severe dehydration quickly. While the exact cause is unknown, it requires urgent veterinary care for IV fluid support.

In puppies, bloody diarrhea is always urgent — parvovirus is the primary concern, especially in unvaccinated pups.