What are the potential causes of hematochezia (passage of fresh blood per anus) in an 18-year-old patient?

Causes of Hematochezia in an 18-Year-Old Patient

In an 18-year-old patient, the most common causes of hematochezia are anorectal conditions (hemorrhoids, anal fissures), infectious colitis, inflammatory bowel disease (particularly ulcerative colitis), and polyps, with the critical imperative being to exclude colorectal cancer despite the young age. 1

Age-Specific Differential Diagnosis Framework

Most Common Causes in Young Adults (18-50 years)

The differential diagnosis in an 18-year-old differs substantially from older adults, where diverticulosis and angiodysplasia predominate. 1 For this age group, prioritize:

Anorectal Conditions (Most Common)

• Hemorrhoids and anal fissures are the leading causes in young adults, though colonoscopy is mandatory before attributing bleeding to these benign sources. 2
• Never assume hemorrhoids without complete evaluation, as this represents a critical diagnostic pitfall. 3, 2

Inflammatory Bowel Disease

• Ulcerative colitis commonly presents in early adulthood with the triad of abdominal pain, diarrhea, and hematochezia. 4
• The incidence of inflammatory bowel disease peaks in early adulthood, making this a key consideration in an 18-year-old. 4

Infectious Colitis

• Bacterial colitis from Salmonella, Campylobacter, or other pathogens is common in young patients. 5
• In a prospective pediatric study extending to age 19, infectious diseases caused 44% of hematochezia cases. 5

Colorectal Neoplasia (Cannot Be Excluded)

• Hematochezia confers a hazard ratio of 10.66 for early-onset colorectal cancer (diagnosed <50 years), with 46% of early-onset cases presenting with rectal bleeding. 1
• Rectal cancers are particularly associated with hematochezia presentations (38% of cases with this symptom). 1

Critical Upper GI Source Exclusion

10-15% of patients presenting with severe hematochezia actually have an upper gastrointestinal bleeding source despite the bright red appearance of blood. 1, 2 This represents a crucial diagnostic consideration that must not be overlooked. 3

Essential Diagnostic Approach

Key Historical Features to Elicit

Red Flag Symptoms Requiring Urgent Evaluation:

• Unexplained weight loss ≥5 kg (associated with OR 2.23 for early-onset colorectal cancer). 1
• Iron deficiency anemia (ferritin <15 ng/dL confers hazard ratio of 10.81 for early-onset colorectal cancer). 1
• Systemic symptoms including fever, abdominal pain, abdominal distention, or fatigue. 1
• Family history of colorectal cancer or inflammatory bowel disease. 4
• Recent antibiotic use (consider antibiotic-associated colitis). 5

Physical Examination Priorities

• Digital rectal examination to assess for masses, fissures, hemorrhoids, or stool consistency. 3
• Vital signs assessment for hemodynamic instability (approximately 15% of acute presentations can involve hypovolemic shock). 3
• Abdominal examination for tenderness, distention, or masses. 1

Laboratory Evaluation

• Complete blood count to assess for anemia and severity of blood loss. 1, 3
• Iron studies (ferritin) if anemia is present. 1
• Erythrocyte sedimentation rate or C-reactive protein may suggest inflammatory bowel disease, though normal values do not exclude it. 4
• Stool culture and testing for infectious pathogens including Salmonella, Campylobacter, C. difficile, and Klebsiella oxytoca. 5
• Consider coagulation studies if personal or family history of bleeding disorders. 3

Mandatory Endoscopic Evaluation

Complete colonoscopy to the cecum is mandatory for any 18-year-old with hematochezia accompanied by:

• Iron deficiency anemia 1, 2
• Unexplained weight loss 1
• Positive fecal occult blood test (even if hemorrhoids are present) 6
• Atypical bleeding pattern 6
• Risk factors for colorectal neoplasia 1, 6

The diagnosis of inflammatory bowel disease is suspected clinically and confirmed through endoscopic biopsy. 4 Anoscopy and flexible sigmoidoscopy represent the minimum evaluation, but complete colonoscopy is preferred as sigmoidoscopy alone misses more than one-fifth of polyps. 3

Critical Pitfalls to Avoid

• Never attribute hematochezia to hemorrhoids without complete colonic evaluation, as hemorrhoids alone do not cause positive fecal occult blood tests and anemia from hemorrhoidal disease is rare (0.5 per 100,000 population). 2, 6
• Do not rely on sigmoidoscopy alone as this misses significant proximal pathology. 3
• Always exclude upper GI bleeding with upper endoscopy if severe bleeding, hypovolemia, or no lower GI source is identified. 2
• Do not dismiss colorectal cancer based on age alone, as early-onset colorectal cancer is increasing and 18-year-olds can develop malignancy. 1

Additional Considerations

In patients with severe ongoing hematochezia requiring transfusion, urgent colonoscopy after oral purge is effective and safe, with a diagnostic yield of 74% for colonic lesions in one prospective study. 7 However, most young patients with hematochezia do not require urgent intervention, as 80-85% of lower GI bleeding stops spontaneously. 1