The presence of blood noticed during or after passing gas or a bowel movement, medically termed hematochezia, originates from the lower gastrointestinal tract, specifically the colon, rectum, or anus. While this experience can be alarming, the causes range from common, minor issues to more serious underlying conditions. Any instance of discovering blood warrants a consultation with a healthcare provider to accurately determine the source and ensure appropriate management.
Assessing the Color and Volume of the Blood
The appearance of the blood offers immediate clues about its origin within the digestive system. Bright red blood indicates fresh bleeding, meaning the source is typically located close to the anal opening, such as the rectum or anus itself. This color suggests the blood has not had time to be chemically altered as it passes through the digestive tract.
In contrast, blood that appears darker red, maroon, or mixed in with the stool suggests a source higher up in the colon or even the small intestine. The darker color results from the blood being exposed to digestive enzymes and bacteria for a longer period before expulsion. Black, tarry stools, known as melena, generally indicate bleeding originating much higher, often in the stomach or upper small intestine, where digestive acid has significantly changed the blood’s hemoglobin.
The amount of blood is also an important factor. Small streaks on toilet paper or drops in the toilet bowl differ from passing large clots or experiencing a sudden, heavy flow. While small amounts may be linked to benign anal conditions, a large volume of blood requires urgent medical evaluation, regardless of its color.
Localized Causes of Rectal Bleeding
The most frequent causes of blood appearing with gas or stool are structural issues located near the anal opening. These conditions often result in bright red blood because the source is close to the exit point.
Hemorrhoids are a very common cause, developing from swollen veins in the lower rectum or anus. Internal hemorrhoids are typically painless but can bleed when strained against or rubbed by passing stool or gas. The increased abdominal pressure from straining during a bowel movement or even a forceful passage of gas can cause these fragile veins to rupture, leading to bleeding.
Another common localized cause is an anal fissure, which is a small tear in the thin tissue lining the anus. Fissures are usually caused by passing hard or large stools, creating a wound highly susceptible to re-injury. The passage of stool or gas stretches the anal canal, reopening the tear and causing a small amount of bright red blood, often accompanied by sharp, intense pain.
Since the bleeding source is superficial, the muscular contractions and pressure changes involved in passing gas or stool can directly irritate the injured tissue, triggering bleeding from a hemorrhoid or fissure.
Internal Conditions Requiring Intervention
While localized issues are common, bleeding can also originate from more significant pathologies higher up in the colon, requiring specific medical intervention. These internal conditions involve changes to the lining or structure of the bowel wall itself.
Inflammatory Bowel Disease (IBD), which includes Ulcerative Colitis and Crohn’s disease, involves chronic inflammation of the digestive tract. Ulcerative Colitis, which affects the colon and rectum, commonly causes bloody diarrhea mixed with mucus due to the ulceration of the lining. Crohn’s disease can affect any part of the digestive tract, and bleeding can occur from deep ulcers within the bowel wall.
Diverticular disease is another major cause, involving small, bulging pouches called diverticula that form on the wall of the large intestine. Bleeding occurs when the small blood vessels near these pouches rupture, often resulting in a sudden, painless, and sometimes substantial amount of dark or bright red blood. Diverticular bleeding is recognized as the most frequent cause of lower gastrointestinal bleeding in older adults.
Growths within the colon, such as colorectal polyps or cancerous tumors, can also cause bleeding. Polyps are small clumps of cells that form on the colon lining. While most are benign, larger ones are more prone to bleeding and may eventually become malignant. Bleeding from polyps or low-lying tumors can manifest as bright red blood, mimicking a benign cause, or as occult blood that causes slow, chronic blood loss.
The Medical Evaluation and Diagnostic Process
Immediate medical attention is necessary if the bleeding is massive, persistent, or accompanied by symptoms like dizziness, fainting, severe abdominal pain, or a rapid heart rate. These signal severe blood loss or a serious acute internal issue.
For less severe, intermittent bleeding, a medical evaluation typically begins with a physical examination, including a digital rectal exam to feel for masses or abnormalities. The physician may also use a small scope, called an anoscopy or proctoscopy, to visually examine the anal canal and lower rectum for hemorrhoids or fissures.
Further investigation often includes tests to check for microscopic amounts of blood not visible to the naked eye. To examine the colon more comprehensively, a flexible sigmoidoscopy may be performed to view the lower part of the colon, or a colonoscopy may be used to visualize the entire large intestine. The colonoscopy is the most thorough procedure, allowing the physician to identify the bleeding source, remove polyps, and take tissue samples for analysis.