A concerned owner called the other day. Solly, the family dog, was passing stools that looked black. Go ahead. Get the giggling out of your system now. We’re gonna talk about poop. There’s no lack of euphemisms for digestive waste, but technically it’s called feces, and feces often give important information about what’s happening inside an animal’s gastrointestinal tract. (Remember this next time you think being a veterinarian is a romantic profession.) So what can it mean, that Solly had this dark stool?
The majority of times when owners report black stool, when I see the sample myself, it is actually just very dark brown, a normal variation. The color of what goes in affects the color of what comes out. “Did anyone give Solly Pepto-Bismol?” I asked. Pepto-Bismol, or any product containing bismuth subsalicylate, can turn stool black. Weird, huh? How does bright pink medication do this? Sulfur in the saliva interacts with the bismuth to form bismuth sulfide … which is black. Ingested charcoal can also make stool black — if Solly chewed on burned wood from the firepit or briquettes spilled from the barbecue, or if a veterinarian intentionally administered activated charcoal, as we might do after a dog ingests certain toxic substances. But, no, Solly hadn’t had bismuth subsalicyclate or charcoal.
“How is he feeling?” I asked. Dark, tar-like stools can indicate bleeding in the upper gastrointestinal tract, anywhere from the nose and mouth down to the small intestines. The blood gets digested, so when it comes out the other end, it is no longer red. The presence of black, tarry stool caused by digested blood is called melena. Most dogs suffering from significant internal hemorrhage will have other signs consistent with blood loss, such as weakness and pale gums. But Solly was feeling fine.
“Is he on any medications?” I asked. There are a large number of drugs that can cause stomach ulcers. Ulcers can cause hemorrhage. Hemorrhage can cause melena. The most common drugs involved in this scenario are nonsteroidal anti-inflammatories, AKA NSAIDs, including veterinary prescription drugs like Rimadyl, Deramaxx, Metacam, or Previcox. Or your veterinarian may dispense generic versions of the same NSAIDs. Owners often make the mistake of giving pets over-the-counter NSAIDs intended for people. Dogs (and cats) are not just furry, four-legged people. These products in your medicine cabinet can cause life-threatening problems if given to your pets. Always check with your veterinarian before administering any medication. I occasionally suggest aspirin for dogs (cat owners: Don’t do it!) but other over-the-counter NSAIDs such as ibuprofen (Advil), or naprosyn (Aleve) can cause nasty problems. Naprosyn in particular can lead to severe gastrointestinal hemorrhage in dogs. Corticosteroids, such as prednisone, are another potentially problematic class of medications frequently prescribed for things such as skin problems and allergies. Most dogs handle them just fine, but rarely, an individual will develop significant gastrointestinal bleeding. With any of these medications, long-term use increases the risk. It’s also important to consider drug interactions. NSAIDs should never be given at the same time as corticosteroids. But Solly wasn’t taking anything.
There are other less common causes of melena: anything that interferes with normal blood clotting such as anticoagulant rat poison, or bleeding disorders such as autoimmune thrombocytopenia. Inflammatory diseases like hemorrhagic gastroenteritis, pancreatitis, and inflammatory bowel disease. Foreign bodies that irritate or perforate the GI tract. Liver or kidney failure, which may lead to clotting problems or stomach ulcers. Cancer. Even intestinal worms, if there are enough of them. Usually such cases will exhibit other signs of illness besides the melena. Not so with hematochezia.
Hemato … what? Hematochezia. That’s the medical term for bright red streaks of blood in the stool, a very different situation from the dark, tarry appearance of melena. In younger dogs, hematochezia is often caused by intestinal parasites, or just by eating stupid things: birdseed, acorns, hair — stuff that irritates the rectum and/or anus on its way out. Older dogs are less likely to have worms, though it never hurts to run a fecal study to rule out such parasites, as well as a test for protozoa like Giardia. I am rarely concerned about a single episode of a little blood in a formed stool if the animal is feeling completely fine otherwise, but persistent hematochezia warrants a trip to the veterinarian. One of the first things we do is examine under the dog’s tail for anal-sac infections, tumors, and other perianal problems such as trauma, fistulas, or hernias. If all looks normal, we then have to decide whether to pursue definitive diagnosis or just try nonspecific therapy.
Many of these dogs have “colitis,” i.e. inflammation of the colon, resulting in diarrhea, straining, increased frequency and urgency of defecation, and mucoid stools, as well as hematochezia. Why is the colon inflamed? Underlying etiologies can run the gamut: food intolerance, stress, many types of infections, cancer. Pinning down the culprit can be difficult. Owners often opt to start with dietary changes, such as feeding bland, easily digested food in multiple, small meals, and empirical medications that may help with colitis, regardless of the cause.
Solly did not have hematochezia. No bright red blood. Did he truly have melena, or was this simply a “false-positive” dark stool? Ah, I hear you thinking. “Can’t she just run that test they do for people to check for blood in the stool?” Nope. The occult fecal blood test requires three days of vegetarian diet prior to testing. Otherwise all we would learn is that Solly eats dog food, dog food contains meat, meat contains blood. Since he didn’t have diarrhea, his appetite was good, and he was feeling fine, I suggested feeding a bland diet and continued observation. If the dark stools persisted or if Solly wasn’t feeling well, they should bring him in. I haven’t heard back, so I am assuming no news is good news. That’s today’s scoop on poop. Now grow up. Stop giggling.