Seeing blood in your feces causes understandable concern. This sign, known medically as hematochezia or melena, indicates bleeding somewhere along the gastrointestinal (GI) tract, which extends from the esophagus to the anus. While some visible blood stems from minor, easily treatable issues, this symptom should never be ignored. A medical evaluation is required to determine the source and severity of the bleeding. The appearance of the blood provides the first important clue, helping to narrow down the potential location of the problem.
Visualizing the Blood: Color and Consistency
The color and texture of the blood in the stool indicate where the bleeding is occurring. Bright red blood, medically termed hematochezia, suggests fresh blood that has not traveled far through the digestive system. This usually points to a source in the lower GI tract, such as the colon, rectum, or anus. The blood remains red because it has not been significantly altered by digestive enzymes or stomach acid.
In contrast, dark, tarry, and often foul-smelling stools, known as melena, typically signify bleeding in the upper GI tract, including the esophagus, stomach, or upper small intestine. The black color results from the blood being digested and chemically changed by acid and enzymes as it passes through a considerable length of the digestive system. Sometimes, the amount of blood is too small to be visible (occult or hidden blood), requiring specialized laboratory tests for detection.
Common Causes in the Lower Gastrointestinal Tract
Bleeding that originates closer to the exit point of the digestive tract often presents as bright red blood. One of the most frequent causes is hemorrhoids, which are swollen blood vessels located in the rectum or around the anus. These fragile vessels can bleed when irritated by straining during a bowel movement or by passing hard stool. Hemorrhoids are generally considered a less severe cause, resulting in small amounts of blood visible on the toilet paper or in the toilet bowl.
Another common source of bright red blood is an anal fissure, which is a small tear in the thin lining of the anal canal. This tear is often caused by the passage of a large or hard stool and typically causes sharp pain during a bowel movement, in addition to the bleeding. A more serious condition is diverticulitis, where small pouches (diverticula) develop in the wall of the colon. When a small blood vessel near a diverticulum bursts, it can cause painless, sometimes significant bleeding. Inflammatory bowel disease (IBD), which includes Crohn’s disease and ulcerative colitis, also causes inflammation and ulcers in the colon that can lead to bloody stool.
Causes and Concerns in the Upper Gastrointestinal Tract
Bleeding that results in the black, tarry stool known as melena usually has its source higher up in the digestive system. The most common cause of upper GI bleeding is a peptic ulcer, which is a sore on the lining of the stomach or the first part of the small intestine (duodenum). These ulcers often bleed, and the blood is darkened by stomach acid as it moves down the tract. Peptic ulcers are frequently caused by infection with the bacterium Helicobacter pylori or by the long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs).
Inflammation of the stomach lining, known as gastritis, can also cause shallow erosions that bleed and lead to melena. Conditions affecting the esophagus may also be responsible, such as esophageal varices—enlarged, fragile veins in the lower esophagus often associated with advanced liver disease. These varices can rupture and cause massive, urgent bleeding. Because the blood loss from the upper GI tract can be rapid and substantial, these causes are generally considered more medically serious than typical lower GI bleeding.
Diagnostic Procedures to Determine the Source
Investigating the source of GI bleeding begins with a physical examination and review of the patient’s medical history and symptoms. Initial laboratory work includes blood tests to check for anemia (signaling chronic blood loss) and stool tests for occult blood. These preliminary steps help to determine the next course of action.
For suspected lower GI bleeding, the primary diagnostic tool is a colonoscopy, which involves inserting a flexible tube with a camera through the rectum to examine the entire large intestine. If the bleeding is suspected to be from the upper GI tract, an upper endoscopy is performed, where a similar scope is passed down the throat to visualize the esophagus, stomach, and duodenum. If the bleeding source remains obscure, tests such as capsule endoscopy (where the patient swallows a pill-sized camera) or angiography (which uses dye and X-rays to visualize blood vessels) may be necessary.
When to Seek Immediate Medical Attention
While many causes of blood in the stool are not life-threatening, certain accompanying signs signal a medical emergency. If you experience a large volume of bright red bleeding that continues without stopping, or if the toilet water turns red with blood, you should seek emergency care. Passing blood clots or experiencing continuous bloody diarrhea also necessitates urgent evaluation.
Any sign of significant blood loss leading to systemic symptoms requires immediate attention. Symptoms include feeling dizzy, lightheaded, or fainting, which suggests the body is going into shock due to rapid blood volume decrease. Other acute symptoms, such as a rapid heart rate, severe abdominal pain, high fever, or persistent vomiting, especially if the vomit looks like coffee grounds, indicate a serious, potentially life-threatening condition. Delaying care in the presence of these symptoms can have severe consequences.