Hematochezia refers to the presence of red or fresh blood in the stools, and must be differentiated from melena, which is the presence of black, tarry stools. The causes, diagnostic tests, and treatment protocols for hematochezia often differ from those for melena.

Hematochezia is often a sign of lower gastrointestinal disease. In some cases it is an indication of a minor, transient problem. In other cases it is indicative of a serious underlying disease that can become an emergency requiring intensive therapy. Hematochezia may be the only clinical sign seen, or it may be accompanied by other signs, especially straining to defecate. Obtaining a detailed history and through physical examination are essential when evaluating these patients.

Causes

There are many potential causes of hematochezia. The most common causes are usually associated with the gastrointestinal tract, although in some cases, the cause is completely unrelated (e.g. clotting disorders or coagulopathies). It is important to determine the cause of hematochezia, as specific treatment is often necessary for these patients.

Numerous infectious agents may result in hematochezia. These include viral infections such as panleukopenia, bacterial infections such as Salmonella, protozoal agents such as coccidiosis, and intestinal parasites such as hookworms and roundworms.

Dietary intolerance and indiscretion from eating spoiled food, overeating, ingesting foreign material (especially bones), a sudden change in diet, or eating people food may cause inflammation of the lower bowel and hematochezia.

Dietary allergy to certain food substances, such as to particular proteins, lactose, high fat content, and certain food additives may also cause colitis with hematochezia.

Masses of the colon, rectum or anus may cause bleeding and produce hematochezia. Such masses include benign (polyps) and malignant (cancer) tumors.

Persistent hematochezia is a common sign of inflammation of the colon, sometimes referred to as colitis. Many of the causes of hematochezia listed above also cause colitis. Colitis can also occur for unknown, immune-related, or poorly defined reasons, and may require a colonic biopsy to identify the type of inflammation present.

Trauma of any sort can cause hematochezia. Examples include bite wounds to the anal area, fractures of the pelvis that disrupt the colon or rectum, the passage of sharp ingested objects (e.g. bones, needles, tacks, etc.), and the insertion of instruments or materials into the rectum (e.g. examination scopes, enema syringes, etc.).

Bleeding disorders (coagulopathies) of the body may result in bleeding from the lining of the lower bowel. There are numerous types of bleeding disorders that may occur in animals. Examples include ingestion of rat poison that contains anticoagulants, inherited clotting disorders (rare in the cat), decreased numbers of platelets (uncommon in the cat), disseminated intravascular coagulation (DIC) from massive infections or organ failure, and severe liver disorders.

Intussusception (the telescoping of one part of the bowel into another) secondary to foreign bodies, tumors, or parasites can cause hematochezia.

Stricture (narrowing) of the anus or colon, secondary to previous trauma, inflammation, cancer or a foreign body may result in bleeding, especially as stools are passed.

Chronic or intermittent constipation and attempted passages of dry, hard stools may result in hematochezia.

Anal sacculitis (inflammation of the anal sacs) or anal sac abscessation can change the consistency of the fluid in the anal sacs to a bloody liquid. This liquid may coat the stools as they are defecated. Anal sac diseases are uncommon in the cat.

Proctitis is inflammation of the rectum and is often associated with colitis.