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

Workup for Mucoid Stools

Begin with stool microbiological testing (bacterial culture, Clostridium difficile toxin assay, and ova/parasites if travel history or shellfish exposure) alongside blood work (CBC, CRP, electrolytes, renal/liver function), then proceed to flexible sigmoidoscopy with biopsies if infection is excluded or if red flag symptoms are present. 1, 2

Initial Clinical Assessment

Document specific stool characteristics including frequency, consistency, presence of blood, urgency, and duration to differentiate acute from chronic processes 2. Key red flags requiring urgent evaluation include:

• Fever >37.8°C, bloody stools, or severe abdominal cramping 1
• Systemic toxicity (pulse >90 bpm, hemoglobin <105 g/L, CRP >30 mg/L) 1
• Weight loss, nocturnal symptoms, or symptoms <3 months duration 2
• Recent travel, antibiotic exposure, or family history of inflammatory bowel disease 1, 2

Laboratory Investigations

Stool studies are the first-line investigation and should not delay initial assessment 1, 2:

• Bacterial culture for Salmonella, Shigella, Campylobacter, Yersinia, and STEC (Shiga toxin-producing E. coli) 1
• Clostridium difficile toxin assay in all patients 1
• Ova and parasites examination if travel history, shellfish consumption, or exposure to brackish water 1, 2
• Multiplex PCR panels are reasonable alternatives offering faster results than conventional culture 3, 4

Blood tests should include 1, 3:

• Complete blood count (assess for anemia, leukocytosis) 3
• CRP or ESR (inflammatory markers) 1, 3
• Comprehensive metabolic panel (electrolytes, renal function, liver function) 3
• Fecal calprotectin or lactoferrin to differentiate inflammatory from non-inflammatory causes, though these lack specificity 2, 3

Endoscopic Evaluation

Flexible sigmoidoscopy is the initial endoscopic procedure of choice 1, 2:

• Perform sigmoidoscopy even if mucosa appears normal, as microscopic changes may be present 2
• Obtain biopsies from at least five sites including rectum and ileum during initial evaluation 1
• In mild-to-moderate disease, colonoscopy with terminal ileal intubation is preferred to assess full disease extent 1, 2
• In moderate-to-severe disease, defer colonoscopy due to perforation risk; flexible sigmoidoscopy is safer 1, 3

Histological features suggestive of ulcerative colitis include basal plasmacytosis, diffuse crypt atrophy and distortion, villous surface irregularity, and mucus depletion 1.

Imaging Studies

Abdominal radiography or CT is essential in suspected severe colitis 1, 3:

• Excludes colonic dilatation, toxic megacolon, or perforation 1
• CT abdomen/pelvis for patients with fever, significant pain, bleeding, or concern for complications 3
• MRI and ultrasound may determine colitis extent but are less sensitive than CT for detecting perforation 1

Diagnostic Algorithm

Step 1: Exclude infection first 2, 3

• Stool cultures, C. difficile assay, and ova/parasites based on risk factors 1, 2
• Do not delay treatment pending culture results if severe colitis is suspected 1

Step 2: Risk stratification 1, 3

• Severe disease indicators: >6 bloody stools/day, fever, hemodynamic instability, WBC ≥15,000 cells/mL, creatinine elevation >50% above baseline 1, 3
• These patients require hospital admission for intensive management 1

Step 3: Interpretation of results 2, 3

• Positive stool cultures: Treat infection appropriately; bacterial colitis causes inflammatory diarrhea with bloody, purulent, mucoid stools 5
• Negative cultures with elevated fecal calprotectin: Proceed to endoscopy to evaluate for inflammatory bowel disease 2, 3
• Negative cultures and normal inflammatory markers: Consider functional disorders, but maintain vigilance for IBD 2

Common Pitfalls

A single comprehensive stool specimen is sufficient when prevalence of infection is up to 20%, providing negative predictive values of approximately 95-98% 6. Examining multiple specimens is unnecessary in most cases unless initial testing is inconclusive 6.

In developing countries or immunocompromised patients, consider atypical parasitic infestations like Blastocystis hominis, which may play a pathogenic role 7. The British Society of Gastroenterology emphasizes that 5-15% of IBD patients cannot be definitively classified as ulcerative colitis versus Crohn's disease and are labeled as IBD-unclassified 1.