What is the initial workup for a patient presenting with mucoid stools?

Workup for Mucoid Stools

Begin with comprehensive stool microbiological testing including bacterial culture, Clostridium difficile toxin assay, and ova/parasites examination, combined with blood work (CBC, CMP, inflammatory markers) and flexible sigmoidoscopy with biopsy to differentiate infectious colitis from inflammatory bowel disease. 1, 2

Initial Clinical Assessment

History Taking

• Document stool characteristics: frequency, consistency, presence of blood, urgency, nocturnal symptoms, and duration (>4 weeks suggests chronic process) 1
• Identify risk factors: recent travel, antibiotic exposure, sexual practices (particularly receptive anal intercourse for infectious proctitis), medication use, smoking history, and family history of IBD 1, 3
• Assess for systemic symptoms: fever, weight loss, abdominal pain, malaise, and extraintestinal manifestations (joint pain, skin lesions, eye symptoms) that suggest IBD 1
• Red flags for organic disease: symptoms <3 months duration, nocturnal/continuous diarrhea, significant weight loss, and blood in stool 1

Physical Examination

• Vital signs: temperature, heart rate, blood pressure to assess for sepsis or hemodynamic instability 2
• Abdominal examination: tenderness, distension, masses, and bowel sounds 1, 2
• Perianal examination: fissures, fistulae, abscesses, or skin tags suggesting Crohn's disease 1
• General assessment: signs of anemia, dehydration, weight loss, and extraintestinal manifestations 1

Laboratory Investigations

Stool Studies (Priority)

• Microbiological testing: bacterial culture for Salmonella, Shigella, Campylobacter, E. coli O157:H7 1, 2, 4
• Clostridium difficile testing: toxin assay or PCR, especially with recent antibiotic exposure 1, 2
• Ova and parasites: particularly with travel history or shellfish consumption 2
• Multiplex PCR panels: reasonable alternative for faster pathogen identification 2
• Fecal calprotectin or lactoferrin: elevated levels suggest inflammatory process (IBD vs. infectious colitis) but lack specificity 1, 2

Blood Tests

• Complete blood count: assess for leukocytosis (suggests infection/inflammation), anemia (chronic disease/bleeding), left shift (bacterial infection) 1, 2
• Comprehensive metabolic panel: electrolytes, renal function, liver function tests 1, 2
• Inflammatory markers: ESR and CRP (elevated in IBD and severe infections, though non-specific) 1, 2
• Consider additional testing: HIV, hepatitis B/C serology if immunosuppression may be needed or risk factors present 2

Endoscopic Evaluation

Sigmoidoscopy/Colonoscopy

• Flexible sigmoidoscopy: recommended for all patients with diarrhea and mucoid stools unless immediate colonoscopy planned 1
• Obtain biopsies: even if mucosa appears normal, as microscopic changes may be present 1
• Colonoscopy with terminal ileal intubation: preferred in mild-moderate disease to assess full extent and obtain terminal ileal biopsy for Crohn's disease evaluation 1
• Defer in severe disease: flexible sigmoidoscopy safer than colonoscopy when perforation risk elevated 1

Endoscopic Findings to Differentiate

• Ulcerative colitis: loss of vascular pattern, granularity, friability, continuous inflammation from rectum proximally 1
• Crohn's disease: focal, asymmetric inflammation, skip lesions, aphthous ulcers 1
• Infectious colitis: variable appearance, may mimic IBD endoscopically 4, 3

Imaging Studies

When to Obtain Imaging

• Abdominal X-ray: if severe symptoms to exclude toxic megacolon, perforation, or assess disease extent 1
• CT abdomen/pelvis: for severe colitis, fever, significant pain, or concern for complications (abscess, perforation) 2
• Small bowel imaging: if Crohn's disease suspected, use MR enterography or CT enterography to evaluate small bowel 1

Diagnostic Algorithm

Step 1: Exclude Infection First

Critical point: 38% of patients presenting with mucoid bloody diarrhea suspected to have IBD actually have infectious colitis 4. Always obtain stool studies before diagnosing IBD.

Step 2: Risk Stratification

• Severe disease indicators: stool frequency >6/day, fever, hemodynamic instability, peritoneal signs, WBC ≥15,000, elevated lactate, creatinine elevation >50% 2
• Severe cases require: hospitalization, IV fluids, urgent GI consultation, and consideration of empiric antibiotics pending cultures 2

Step 3: Interpret Results

• Positive stool cultures: treat infectious colitis appropriately, consider co-infections (especially sexually transmitted if proctitis) 2, 3
• Negative cultures with elevated fecal calprotectin and endoscopic/histologic inflammation: likely IBD, proceed with disease extent assessment and classification 1
• Negative workup with persistent symptoms: consider functional disorders, but ensure adequate follow-up as IBD can evolve 1

Common Pitfalls to Avoid

• Do not assume IBD without excluding infection: infectious agents (Campylobacter, Salmonella, Shigella, C. difficile, Entamoeba) can perfectly mimic IBD endoscopically 5, 4
• Do not overlook sexually transmitted proctitis: particularly in patients with receptive anal intercourse; test for Neisseria gonorrhoeae, Chlamydia trachomatis, HSV, and syphilis 3
• Do not delay endoscopy: histology is essential for definitive diagnosis and cannot be replaced by stool or blood tests alone 1
• Do not start immunosuppression before excluding infection: this can worsen infectious colitis and lead to severe complications 1

Special Considerations

• Refractory symptoms on IBD treatment: reconsider diagnosis and evaluate for IBD mimics including opportunistic infections, C. difficile superinfection, cytomegalovirus colitis, medication effects, or bile acid malabsorption 6
• Coexisting conditions: IBD and infections can coexist; maintain high suspicion for superimposed infection in known IBD patients with symptom flares 6