In a 34-year-old otherwise healthy man with a 5‑day history of increased bowel frequency, urgency with small or no stool, rectal bleeding and mucoid discharge, but no abdominal pain, nausea, vomiting, heartburn, dysphagia, odynophagia, abdominal distension, constipation, hypothyroid symptoms, or recent outside food exposure, what is the appropriate diagnostic work‑up and initial management?

Immediate Diagnostic Work-Up and Management

This patient requires urgent colonoscopy with biopsies, stool studies for infection (including culture, ova and parasites, and C. difficile), and measurement of inflammatory markers (CRP, CBC, albumin, and fecal calprotectin) to differentiate between infectious colitis and inflammatory bowel disease. 1

Algorithmic Approach to Diagnosis

Step 1: Initial Laboratory Assessment

• Blood tests: Full blood count (looking for anemia from bleeding, leukocytosis suggesting inflammation), CRP, albumin 1
• Stool studies:
  • Bacterial culture (Salmonella, Shigella, Campylobacter, E. coli O157:H7)
  • Ova and parasites
  • C. difficile toxin
  • Fecal calprotectin: Excellent sensitivity for IBD but poor specificity—infections also elevate it 1, 2

Step 2: Endoscopic Evaluation

Full colonoscopy with segmental biopsies is mandatory 1. The clinical presentation—increased frequency, urgency with tenesmus (sensation to defecate with minimal/no stool), rectal bleeding, and mucoid discharge—strongly suggests distal colonic inflammation, most consistent with either:

• Ulcerative colitis (new-onset IBD)
• Infectious colitis (proctocolitis)

The 2025 BSG guidelines emphasize that diagnosis of ulcerative colitis requires colonoscopy with histology, as endoscopic appearance alone may underestimate disease extent 1. Segmental biopsies are critical even in areas that appear normal endoscopically.

Why not flexible sigmoidoscopy? While research shows sigmoidoscopy captures 95% of substantial lesions in hematochezia 3, the guideline-based approach for suspected IBD requires full colonoscopy to establish disease extent, which directly impacts prognosis and treatment 1. Disease extent determines colectomy risk: 19% at 10 years for extensive colitis versus 5% for proctitis.

Step 3: Risk Stratification During Evaluation

Red flags requiring urgent assessment:

• Hemoglobin drop suggesting significant bleeding
• Fever or systemic toxicity
• Severe diarrhea (>6 stools/day with blood)
• Abdominal tenderness developing

If acute severe colitis develops, unprepared flexible sigmoidoscopy is appropriate initially, with planned colonoscopy later 1.

Clinical Reasoning

Why This is Likely IBD (Ulcerative Colitis):

• Age 34: Peak incidence for IBD
• Tenesmus with urgency: Classic for distal colonic inflammation, independently associated with histologic inflammation even when endoscopy appears normal 4
• Mucoid discharge: Suggests mucosal inflammation
• No pain: Ulcerative colitis often presents without significant abdominal pain, unlike Crohn's disease
• Short duration (5 days) with persistent symptoms: Infectious causes typically resolve or worsen more dramatically

Why Infection Must Be Excluded:

The 2017 IDSA guidelines emphasize that stool cultures and testing must be performed before assuming IBD 2. Infections can mimic IBD completely and treating presumed IBD with immunosuppression when infection is present causes catastrophic outcomes 5.

Common pitfall: Starting corticosteroids or biologics before excluding infection. Always obtain stool studies first.

Initial Management Pending Results

Symptomatic Treatment:

• Hydration: Oral or IV depending on severity
• Avoid NSAIDs: Can worsen colitis
• No empiric antibiotics: Unless sepsis or specific pathogen identified 2
• No antidiarrheals: Risk of toxic megacolon if severe colitis

Monitoring:

• Daily hemoglobin if bleeding continues
• Vital signs for hemodynamic instability
• Stool frequency and character

Safety Netting Instructions

Return immediately or call if:

• Fever >38°C develops
• Dizziness, lightheadedness, or fainting (suggesting significant blood loss)
• Abdominal pain develops or worsens
• Stool frequency increases to >6 times daily
• Pure blood without stool
• Unable to tolerate oral fluids

Follow-up within 48-72 hours for:

• Laboratory results review
• Colonoscopy scheduling (should occur within 1-2 weeks if stable)
• Reassessment of bleeding and symptoms

Special Considerations

If all testing is negative (colonoscopy normal, biopsies normal, stool studies negative, normal inflammatory markers), consider:

• Small bowel pathology (Meckel's diverticulum, though rare at age 34) 6, 7
• Vascular lesions (angiodysplasia, ectasias) 8
• Capsule endoscopy or CT/MR enterography as next steps

However, normal endoscopy does NOT exclude IBD—histology may show microscopic inflammation 1. This is why biopsies are non-negotiable even with normal-appearing mucosa.

The combination of urgency, tenesmus, rectal bleeding, and mucoid discharge in a young adult without infectious exposure makes new-onset ulcerative colitis the leading diagnosis until proven otherwise, but systematic exclusion of infection and complete endoscopic/histologic evaluation are mandatory before initiating IBD-specific therapy.