Rectal Bleeding: What Could Be Causing It

How Common Is Rectal Bleeding?

Rectal bleeding is one of the most frequent gastrointestinal complaints seen in primary care and emergency departments. Population-based surveys estimate that roughly 14% of adults experience at least one episode of rectal bleeding per year, though fewer than half seek medical attention [1]. The clinical term for visible red or maroon blood from the rectum is hematochezia, distinguishing it from melena (black, tarry stools originating higher in the GI tract).

Most episodes originate from benign anorectal conditions. A prospective UK study of 487 patients referred for rectal bleeding found that hemorrhoids accounted for 38.6% of diagnoses, while colorectal cancer was identified in 3.4% [2]. That gap matters. The overwhelming majority of people who notice blood on their toilet paper do not have cancer, but the minority who do benefit enormously from early detection. A 2020 BMJ analysis found that patients presenting with rectal bleeding had a positive predictive value for colorectal cancer of approximately 2.4% to 7.5%, depending on age and accompanying symptoms [3]. The challenge for clinicians is stratifying who needs urgent investigation from who can be managed conservatively.

Age shifts the probability. In patients under 40 without alarm features, benign causes dominate. Over 50, the pretest probability of neoplasia rises substantially. The American Gastroenterological Association's 2023 clinical practice update specifically recommends that all patients over 45 with new hematochezia undergo colonoscopy rather than assuming a hemorrhoidal source [4].

Hemorrhoids: The Most Common Culprit

Internal hemorrhoids cause painless, bright red bleeding that patients typically notice on the paper, dripping into the bowl, or coating the stool surface. They account for the largest single share of rectal bleeding diagnoses across multiple cohort studies [2].

Hemorrhoids are graded I through IV. Grade I hemorrhoids bleed but do not prolapse. Grade II prolapse with straining but reduce spontaneously. Grade III require manual reduction, and Grade IV are irreducible. Most bleeding comes from Grade I and II disease. The underlying pathology involves engorgement and downward displacement of the anal cushion vascular plexus, not simple "varicose veins" as commonly described.

Conservative treatment resolves symptoms in the majority. Fiber supplementation (targeting 25 to 30 grams daily), adequate hydration, and avoidance of prolonged straining form the foundation. A Cochrane review of seven trials (N=378) found that fiber supplements reduced the risk of persistent hemorrhoid symptoms by 47% compared to placebo (RR 0.53, 95% CI 0.38 to 0.73) [5]. Office-based procedures such as rubber band ligation are effective for Grade I to III hemorrhoids that fail conservative management. The procedure has a success rate of 60% to 80% for bleeding control with a single session [6].

External hemorrhoids, by contrast, cause pain rather than bleeding unless they thrombose and erode through the overlying skin. Thrombosed external hemorrhoids present as a tender, bluish perianal lump.

Anal Fissures

An anal fissure is a linear tear in the anoderm, typically at the posterior midline. The hallmark presentation is sharp, tearing pain during and immediately after bowel movements, accompanied by small-volume bright red blood. Fissures are the second most common cause of anorectal bleeding [7].

Acute fissures (present for <6 weeks) heal in most patients with conservative measures: sitz baths, stool softeners, and topical analgesics. Chronic fissures persist because of internal sphincter spasm that reduces blood flow to the fissure base. Topical nitroglycerin 0.4% ointment or topical diltiazem 2% gel are first-line pharmacologic therapies. A randomized trial comparing topical diltiazem to nitroglycerin in 102 patients found healing rates of 65% and 60% respectively, with fewer headaches in the diltiazem group [8]. For refractory chronic fissures, lateral internal sphincterotomy remains the definitive treatment, with healing rates exceeding 90% [7].

Fissures located off the midline (lateral position) should raise suspicion for Crohn disease, tuberculosis, HIV-related ulceration, or malignancy. These atypical fissures warrant biopsy and further workup.

Inflammatory Bowel Disease

Ulcerative colitis and Crohn disease are chronic inflammatory conditions that frequently present with bloody diarrhea. In ulcerative colitis, the inflammation is continuous and confined to the mucosa, starting at the rectum and extending proximally. Bloody stools with mucus, urgency, and tenesmus are the cardinal features.

Crohn disease can affect any segment of the GI tract, and rectal bleeding is less universal than in ulcerative colitis. When Crohn involves the colon or rectum, bleeding can be significant. Perianal disease (fistulae, abscesses, complex fissures) is present in up to 40% of patients with colonic Crohn disease [9].

Diagnosis rests on a combination of endoscopy with biopsy, imaging, and laboratory markers. Fecal calprotectin has emerged as a useful noninvasive screening tool. A meta-analysis of 13 studies (N=1,062) found that fecal calprotectin at a cutoff of 50 mcg/g had a pooled sensitivity of 93% and specificity of 96% for distinguishing IBD from irritable bowel syndrome [10]. The American College of Gastroenterology guidelines recommend checking fecal calprotectin as a first step in patients with chronic diarrhea and bleeding when IBD is suspected [11].

Treatment depends on disease severity and extent. For mild to moderate ulcerative colitis, 5-aminosalicylates (mesalamine) remain the first-line induction and maintenance therapy. Moderate to severe disease often requires biologic agents. Dr. David Rubin, Chief of Gastroenterology at the University of Chicago, has stated: "Early introduction of advanced therapies in moderate-to-severe IBD reduces the long-term risk of complications, hospitalizations, and surgery" [11].

Colorectal Cancer and Polyps

Colorectal cancer is the diagnosis that drives clinical urgency around rectal bleeding. It is the third most common cancer in the United States and the second leading cause of cancer death, with an estimated 153,020 new cases in 2023 [12]. Rectal bleeding is present in approximately 40% of patients at diagnosis, making it one of the most common presenting symptoms [3].

The bleeding pattern in colorectal cancer varies by tumor location. Left-sided and rectal tumors tend to produce visible red blood mixed with stool. Right-sided (proximal) tumors more often cause occult bleeding and iron-deficiency anemia rather than overt hematochezia. Accompanying alarm features include unintentional weight loss, change in bowel caliber, new-onset constipation or diarrhea lasting more than four weeks, and abdominal pain.

The adenoma-carcinoma sequence means that most colorectal cancers arise from precancerous polyps over a 10 to 15 year period. This long dwell time makes screening highly effective. The USPSTF recommends screening for colorectal cancer in all adults aged 45 to 75 years, with colonoscopy every 10 years, annual fecal immunochemical testing (FIT), or stool DNA testing every 1 to 3 years as acceptable options [13]. The National Polyp Study demonstrated that colonoscopic polypectomy reduced colorectal cancer incidence by 76% to 90% compared to reference populations [14].

Any patient over 45 with new rectal bleeding should be evaluated with colonoscopy. The threshold drops even lower for patients with a family history of colorectal cancer, Lynch syndrome, or longstanding IBD.

Diverticular Bleeding

Diverticular hemorrhage is the most common cause of acute, large-volume lower GI bleeding in adults over 60. It accounts for approximately 30% to 40% of significant lower GI bleeding episodes requiring hospitalization [15]. The bleeding originates from an arterial vessel (vasa recta) that becomes draped over the dome of a diverticulum and erodes.

The typical presentation is sudden, painless passage of a large volume of maroon or bright red blood. Most episodes stop spontaneously. A retrospective analysis of 1,514 patients hospitalized for diverticular bleeding found that 76% stopped without intervention [15]. Recurrence rates, however, are substantial: 14% at one year and up to 38% at four years.

Colonoscopy performed within 24 hours of presentation (urgent colonoscopy) can identify the bleeding source in 20% to 40% of cases and allows for endoscopic hemostasis with clips, epinephrine injection, or thermal coagulation. The 2023 American College of Gastroenterology guidelines recommend urgent colonoscopy after adequate bowel preparation for patients with severe hematochezia and hemodynamic stability [16].

For patients with recurrent diverticular bleeding from an identified segment, segmental colectomy is definitive but reserved for cases that fail endoscopic and angiographic management.

Anorectal and Colonic Infections

Infectious colitis and proctitis can produce bloody diarrhea that mimics IBD. Common pathogens include Clostridioides difficile, Shigella, Salmonella, Campylobacter, and enterohemorrhagic Escherichia coli (EHEC, particularly O157:H7). In sexually transmitted proctitis, Neisseria gonorrhoeae, Chlamydia trachomatis (including lymphogranuloma venereum serovars), and herpes simplex virus are the primary causes.

C. difficile infection deserves special attention. It is the most common healthcare-associated infection in the United States, causing an estimated 223,900 cases and 12,800 deaths annually [17]. Bloody stools occur in approximately 5% to 10% of C. difficile cases and suggest severe or fulminant disease. The Infectious Diseases Society of America recommends nucleic acid amplification testing (NAAT) or a two-step algorithm (GDH plus toxin EIA) for diagnosis [17].

Traveler's diarrhea with blood (dysentery) should prompt stool cultures and consideration of empiric fluoroquinolone or azithromycin therapy, depending on the region of travel and local resistance patterns.

Ischemic Colitis

Ischemic colitis results from transient hypoperfusion of the colon, most often affecting the "watershed" areas at the splenic flexure and rectosigmoid junction. It typically presents in older adults with sudden left-sided abdominal cramping followed by bloody diarrhea within 24 hours.

The condition is usually self-limited, resolving with supportive care (IV fluids, bowel rest, avoidance of vasoconstrictors) in 80% to 85% of cases. CT with IV contrast shows segmental colonic wall thickening, and colonoscopy reveals mucosal edema, hemorrhage, and ulceration in a segmental distribution. Dr. Lawrence Brandt, a leading authority on mesenteric ischemia at Albert Einstein College of Medicine, has noted: "The hallmark of ischemic colitis is its segmental, watershed distribution. Circumferential involvement or right-sided ischemia should prompt evaluation for acute mesenteric ischemia, which is a surgical emergency" [18].

Risk factors include atherosclerosis, atrial fibrillation, recent cardiovascular surgery, constipation-inducing medications, and use of cocaine or other vasoconstrictors. Full-thickness necrosis or peritonitis mandates surgical resection.

Radiation Proctitis

Patients with a history of pelvic radiation therapy (for prostate, cervical, rectal, or endometrial cancer) can develop chronic radiation proctitis months to years after treatment. The condition results from obliterative endarteritis of the rectal vasculature, producing telangiectasias that bleed.

Chronic radiation proctitis affects 5% to 20% of patients who receive pelvic radiation [19]. Bleeding ranges from mild intermittent spotting to transfusion-dependent hemorrhage. Endoscopic argon plasma coagulation (APC) is the first-line treatment, with bleeding control achieved in 80% to 90% of patients after one to three sessions [19]. Topical formalin application and hyperbaric oxygen therapy are second-line options for refractory cases.

Less Common Causes

Several other conditions can present with rectal bleeding and should remain on the differential:

Solitary rectal ulcer syndrome occurs from chronic straining and rectal prolapse. The ulcer is typically on the anterior rectal wall 5 to 10 cm from the anal verge and is confirmed by biopsy showing fibromuscular obliteration of the lamina propria.

Dieulafoy lesion is a submucosal artery that bleeds without an overlying ulcer. It is rare in the colon but can cause massive hemorrhage.

Rectal varices develop in patients with portal hypertension and should be distinguished from hemorrhoids. They are found above the dentate line and require different management (portal pressure reduction, TIPS) rather than banding.

Meckel diverticulum is the most common cause of significant lower GI bleeding in children and young adults under 18. Ectopic gastric mucosa within the diverticulum produces acid that ulcerates the adjacent ileal mucosa. A technetium-99m pertechnetate scan (Meckel scan) has a sensitivity of approximately 85% in pediatric patients [20].

When to Seek Urgent Evaluation

Not all rectal bleeding requires emergency care, but certain features demand immediate evaluation. Large-volume bleeding soaking through clothing or filling the toilet bowl, passage of large clots, lightheadedness or syncope, heart rate above 100, systolic blood pressure below 90 mmHg, and hemoglobin <7 g/dL all indicate significant hemorrhage requiring hospital-based resuscitation and endoscopy.

The Oakland score is a validated tool for risk-stratifying acute lower GI bleeding. It incorporates age, sex, prior lower GI bleeding, heart rate, systolic blood pressure, hemoglobin, and digital rectal examination findings. A score of 8 or less identifies patients safe for outpatient management, while scores above 8 predict need for intervention [21]. The original validation study (N=2,336) found that a score of 8 or less had a 95.6% negative predictive value for the composite outcome of transfusion, rebleeding, therapeutic intervention, or death [21].

Even in the absence of these acute indicators, any adult over 45 with new-onset rectal bleeding, any patient with bleeding persisting beyond two weeks, and anyone with concurrent iron-deficiency anemia or weight loss should undergo colonoscopy.

Diagnostic Workup

The evaluation begins with a focused history and physical examination, including digital rectal examination and anoscopy. Laboratory work should include a complete blood count, comprehensive metabolic panel, coagulation studies, and type and screen if bleeding is significant.

Colonoscopy is the primary diagnostic and therapeutic procedure. It allows direct visualization, biopsy, and treatment (polypectomy, hemostatic clip placement, thermal coagulation). For patients with massive bleeding precluding adequate colonoscopic visualization, CT angiography can detect active extravasation at rates as low as 0.3 to 0.5 mL per minute and guides subsequent catheter-directed angiography with embolization [22].

Capsule endoscopy and deep enteroscopy are reserved for cases where upper endoscopy and colonoscopy are nondiagnostic and a small bowel source is suspected.

Treatment Principles

Treatment is cause-specific. Conservative management with fiber, hydration, and sitz baths addresses most hemorrhoidal and fissure-related bleeding. Endoscopic therapy (banding, clipping, APC, injection) treats bleeding from polyps, diverticula, angiodysplasia, and radiation proctitis. Medical therapy targets underlying conditions: mesalamine and biologics for IBD, antibiotics for infectious causes, and portal pressure reduction for variceal bleeding.

Surgical intervention is reserved for massive hemorrhage unresponsive to endoscopic and angiographic management, perforation, and malignancy. For colorectal cancer detected at an early stage (Stage I), five-year survival exceeds 90%, reinforcing the importance of prompt investigation [12].

Patients on anticoagulants (warfarin, apixaban, rivaroxaban) or antiplatelet agents (aspirin, clopidogrel) present a management challenge. These medications amplify bleeding but are rarely the primary cause. Decisions about holding or reversing anticoagulation must balance bleeding severity against thrombotic risk and should involve the prescribing clinician.