I'm sorry that your question wasn't answered in a timely manner. There are quite a few causes of hematochezia (blood in or on the stool) or bleeding originating from the rectum itself. Here's a synopsis of hematochezia for you from Clinical Veterinary Advisor, 3rd Ed., Cote', 2015...The most important words in the following synopsis are:
- Evaluation begins with history, physical exam, and digital rectal exam. Please read the synopsis and then return to our conversation with additional information and further questions or concerns.
The presence of red blood on the surface of or admixed into the stool
Species, Age, Sex
Dependent on underlying cause
- Neoplasia more likely in older animals
- Histiocytic ulcerative colitis: dogs < 2 years old
- Perineal hernia: adult/older, male intact dogs
The most common risk factor for hematochezia is colitis of any cause. Neoplasia is less commonly responsible. Coagulopathies are a rare cause of hematochezia.
Clinically significant anemia very uncommonly occurs as a result of hematochezia.
History, Chief Complaint
- Concurrent mucus in the stool, tenesmus (both are common), painful defecation, “scooting” behavior, licking/chewing/scratching the perineum are common manifestations of colonic or anorectal disease.
- Animals with isolated hematochezia rarely present signs of systemic illness.
- Weight loss and inappetence can occur with concurrent small-intestinal or pancreatic disease, histiocytic ulcerative colitis, or neoplasia.
Physical Exam Findings
- Generally clinically healthy
- The perianal area may be soiled with blood, fecal material, and/or mucus.
- The anus may be inflamed, ulcerated, or painful.
- A mass (neoplasm), swelling (anal sac abscess, perineal hernia, or neoplasm), or fissure (perianal fistula) around the anus may be visible.
- A digital rectal examination is essential in any patient with hematochezia (intraluminal or extraluminal mass, stricture, anal sac mass or abscess, pain, melena).
Etiology and Pathophysiology
- The blood is fresh (undigested), localizing the problem to the descending colon, rectum, or anus.
- Conversely, melena represents oxidized blood as seen with digested blood. Rarely, colonic disorders may produce melena, instead of hematochezia, if colonic transit times are substantially increased (e.g., constipation).
- Evaluation begins with history, physical exam, and digital rectal exam.
- In otherwise well animals with normal physical exam findings, diagnostic testing can begin with fecal analysis and/or response to nonspecific, supportive treatment.
- Further diagnostic evaluation is required in animals with signs of systemic illness, physical exam abnormalities, bleeding diathesis, and/or chronic/recurrent hematochezia.
For detailed differential diagnosis, see p. 1283.
- Anus (e.g., anal sac disorders [see p. 57], perianal fistula, neoplasia, trauma)
- Rectum and colon (e.g., colitis [most common], parasites, neoplasia, stress-associated)
- Visual and digital anorectal examination, including anal sac palpation
- Fecal flotation and direct examination for parasites
- Fecal smear, culture for fecal pathogens, Clostridium enterotoxin detection
- Results of trial therapy (see Acute General Treatment, below)
Advanced or Confirmatory Testing
Further diagnostic evaluation is required in animals with signs of systemic illness, physical exam abnormalities, bleeding diathesis, and/or chronic/recurrent hematochezia.
- Serum biochemistry profile
- Coagulation profile
- Abdominal radiographs, ultrasound
Initial therapy consists of dietary change, broad-spectrum dewormer, and an antibiotic to control bacterial overgrowth. Unresponsive chronic cases may benefit from referral to a specialist for colonoscopy.
Acute General Treatment
Nonspecific trial therapy can be attempted in an animal without systemic signs:
- Dietary modification as dictated by underlying disorder
- Broad-spectrum anthelmintic (e.g., fenbendazole 50 mg/kg PO q 24h × 3 days)
- Trial course of metronidazole (e.g., 7.5-10 mg/kg PO q 12h × 10 days), or tylosin (10 mg/kg PO q 8h for 21 days as treatment trial if suspecting inflammatory bowel disease, or 20 mg/kg PO q 12h for clostridial colitis), sulfasalazine (dogs: 20-40 mg/kg PO q 8h for 14-21 days, then taper by 25%-30% q 14-21 days; cats [use with caution given salicylate sensitivity]: 10-20 mg/kg PO q 24h maximum of 10 days, then taper to lowest effective dose/discontinue)
Specific treatment depends on the underlying disease.
Prognosis & Outcome
Dependent on underlying disease
Pearls & Considerations
Hematochezia should not be confused with melena (dark, tarry stool typically caused by digested blood from stomach or small intestine).