The appearance of blood mixed with or separate from feces, known medically as hematochezia or melena depending on its presentation, indicates bleeding somewhere within the gastrointestinal (GI) tract. While the sight of blood is alarming, the source is often benign and easily treatable. However, any instance of blood in the stool requires prompt evaluation by a healthcare professional to determine the exact cause and rule out serious conditions. Understanding the characteristics of the blood provides initial clues that guide the medical assessment.
Understanding the Visual Clues
Bright red blood, known as hematochezia, typically points to bleeding in the lower part of the GI tract. This fresh appearance indicates the blood has traveled a relatively short distance without undergoing significant chemical changes. Sources are usually found in the colon, rectum, or anus, where the blood may appear as streaks on the outside of the stool or mixed in with it. Rapid transit can sometimes cause blood originating from the upper GI tract to maintain its red color.
A distinctly different appearance is melena, which is characterized by black, sticky, and tarry feces that often possess a foul odor. This dark color is the result of blood being exposed to digestive enzymes and stomach acid over a longer period. The iron in the hemoglobin is chemically altered, yielding the dark, paint-like consistency. Melena strongly suggests that the bleeding originates high up in the digestive tract, such as the stomach or the small intestine.
Producing true melena requires substantial blood loss in the upper GI tract and a transit time long enough for the blood to be fully processed into the tarry consistency. If the bleeding source is in the small intestine or the proximal (upper) colon, the resulting stool may present as a maroon color. This intermediate presentation suggests the blood has been partially digested but not enough to produce the jet-black color of melena.
Sometimes, blood is not visible to the naked eye but is still present in the feces, a condition known as occult bleeding. This hidden blood may be a sign of slow, chronic blood loss from various parts of the GI tract. The color and consistency of the stool provide immediate, though not definitive, clues that guide the initial assessment of the bleeding location.
Common Sources of Gastrointestinal Bleeding
The most frequent cause of bright red hematochezia is often benign hemorrhoids, which are swollen veins located in the lower rectum and anus. Straining during bowel movements or prolonged sitting can irritate these vessels, leading to painless bleeding that typically appears as streaks on the toilet paper or in the bowl. Similarly, anal fissures, which are small tears in the lining of the anal canal, can cause sharp pain during defecation along with small amounts of bright red blood.
Moving higher up the colon, diverticulosis is a common source of significant, painless lower GI bleeding, particularly in older adults. This condition involves the formation of small pouches, called diverticula, that protrude through the muscular wall of the colon. When a small blood vessel adjacent to a diverticulum ruptures, it can cause a sudden and large volume of bright or dark red blood to pass.
Inflammatory Bowel Disease (IBD), which encompasses Crohn’s disease and ulcerative colitis, causes chronic inflammation that damages the lining of the GI tract. Ulcerative colitis affects the large intestine and rectum, frequently causing bloody diarrhea mixed with mucus due to widespread mucosal ulceration. Crohn’s disease can affect any part of the digestive tract, and bleeding occurs when deep ulcers erode into the blood vessels.
Colorectal polyps and cancer can cause slow, chronic bleeding often detected only through occult blood tests. Polyps are growths on the inner lining of the colon or rectum that may evolve into cancer over time. Bleeding from these lesions is typically intermittent and low-volume, making it a subtle indicator of disease progression.
Sources responsible for black, tarry melena are typically found in the upper GI tract, with peptic ulcers being a common cause. These ulcers are open sores that develop on the lining of the stomach or the duodenum, the first part of the small intestine. Bleeding occurs when the acidic environment erodes the ulcer deep enough to penetrate a nearby artery or vein.
Esophageal varices are a source of upper GI bleeding, often seen in individuals with advanced liver disease, such as cirrhosis. High blood pressure in the portal vein system causes collateral veins in the esophagus to enlarge and become fragile. These thin-walled vessels are susceptible to rupture, leading to massive hemorrhage that can present as either melena or hematemesis (vomiting blood).
Gastritis, which is inflammation of the stomach lining, can also lead to upper GI bleeding, though often less severely than ulcers or varices. The inflammation can cause shallow erosions in the mucosal surface, resulting in slow, persistent blood loss. Certain medications, particularly nonsteroidal anti-inflammatory drugs (NSAIDs) and high alcohol intake, are common precipitants of both gastritis and peptic ulcer formation.
Medical Investigation and Diagnosis
When evaluating blood in the stool, a healthcare provider begins by taking a thorough patient history and performing a physical examination, including a digital rectal exam (DRE). The DRE can often immediately identify common, lower-lying causes like hemorrhoids or fissures. Initial laboratory work involves blood tests to assess for anemia, which accompanies chronic blood loss, and to check clotting factors.
To confirm the source of bleeding, specialized diagnostic tools are utilized, often starting with endoscopy. A colonoscopy is the standard procedure for investigating the lower GI tract, allowing the physician to visualize the colon lining, identify lesions, and even treat minor bleeding sources directly. Conversely, an esophagogastroduodenoscopy (EGD) is used to examine the esophagus, stomach, and duodenum, targeting potential upper GI bleed locations.
For bleeding in the small intestine, which is inaccessible by standard EGD or colonoscopy, a capsule endoscopy may be employed. The patient swallows a small camera that transmits images wirelessly as it passes through the digestive tract. Stool tests, such as the fecal immunochemical test (FIT), are also used to detect occult blood not visible to the eye, often as a screening tool for colorectal cancer.
Certain symptoms demand immediate emergency attention. Large-volume blood loss, especially when accompanied by signs of shock like dizziness, confusion, or fainting, requires immediate care. Severe, sudden abdominal pain and a rapid heart rate alongside the bleeding are also red flags requiring an immediate call for emergency services.