What is the recommended diagnostic workup and treatment approach for a patient presenting with acute colitis?

Acute Colitis: Diagnostic Workup and Treatment

For patients presenting with acute colitis, immediately assess severity using Truelove and Witts criteria (≥6 bloody stools/day plus systemic toxicity signs), obtain urgent blood work (FBC, CRP, U&E, LFTs with albumin), stool cultures including Clostridioides difficile and CMV testing, perform flexible sigmoidoscopy with biopsies, and initiate IV corticosteroids (methylprednisolone 40-60mg/day or hydrocortisone 100mg QID) if acute severe ulcerative colitis (ASUC) is confirmed. 1

Initial Risk Stratification and Diagnosis

The first critical step is determining whether this represents acute severe ulcerative colitis (ASUC), which is a medical emergency with 1% mortality. ASUC is defined by:

• ≥6 bloody stools per day PLUS at least one of:
  • Tachycardia (pulse >90 bpm)
  • Fever (>37.8°C)
  • Anemia (Hgb <105 g/L)
  • Elevated ESR (>30 mm/h) or CRP

1

Common pitfall: Don't delay hospitalization while pursuing outpatient workup. ASUC requires immediate admission—approximately 25% of UC patients will experience this at some point, often as their initial presentation. 1

Mandatory Urgent Investigations

Upon hospital admission, obtain simultaneously:

Laboratory studies:

• Complete blood count, CRP, electrolytes, renal function, liver function tests with albumin
• These guide both diagnosis and prognostic assessment 1

Infectious workup (critical before escalating immunosuppression):

• Stool culture for bacterial pathogens
• Clostridioides difficile testing (mandatory—present in up to 82% of audited cases) 2
• CMV testing (only performed in 30% of cases historically, but essential) 2
• Consider multiplex PCR followed by guided culture for rapid pathogen identification 3

Endoscopic evaluation:

• Flexible sigmoidoscopy (not full colonoscopy in acute setting to minimize perforation risk)
• Obtain biopsies to distinguish infectious colitis, IBD, ischemic colitis, and confirm CMV infection
• Biopsies are decisive in differentiating acute colitis etiologies 4

Imaging:

• Non-invasive imaging (CT abdomen) to exclude toxic megacolon and assess disease extent 1

First-Line Treatment for ASUC

Intravenous corticosteroids are the cornerstone of ASUC management, with approximately two-thirds of patients responding. 1

Corticosteroid Dosing (Critical Detail)

Use methylprednisolone 30mg every 12 hours (60mg/day total) OR hydrocortisone 100mg four times daily. 1, 5

• Methylprednisolone is preferred over hydrocortisone because it has less mineralocorticoid effect and causes significantly less hypokalemia 1
• Do NOT use higher doses—doses above 60mg methylprednisolone equivalent offer no additional benefit and increase adverse events 1, 5
• Meta-regression controlling for disease severity showed no correlation between higher corticosteroid doses and reduced colectomy risk 5

Treatment Duration and Response Assessment

• Assess response at 72 hours using validated criteria 6
• Switch to oral corticosteroids when clinically appropriate, usually within 7 days 1
• Do NOT continue IV steroids beyond 7-10 days—prolonged courses carry no additional benefit and increase toxicity without reducing colectomy risk 1, 5

Essential Supportive Measures

VTE prophylaxis (frequently overlooked):

• Patients with ASUC have increased venous thrombosis risk
• Administer appropriate anticoagulant prophylaxis—this does NOT precipitate or exacerbate colonic bleeding 1
• Historical adherence was only 43%, improving to 75% post-guideline publication 2

Avoid adjunctive antibiotics:

• In the absence of confirmed infection, do NOT use adjunctive antibiotics 5

Nutritional optimization and close monitoring are essential components 6

Second-Line Therapy for Steroid-Refractory Disease

If no response after 3-5 days of IV corticosteroids (approximately one-third of patients), escalate to rescue therapy:

Options include:

• Infliximab (anti-TNF)
• Cyclosporine (2mg/kg with trough level monitoring)
• JAK inhibitors (tofacitinib, upadacitinib)—emerging option with limited but promising data 1, 6

These therapies are equally effective; choice should be individualized based on patient comorbidities, age, frailty status, and contraindications. 6, 7

Critical timing: Early surgical consultation is mandatory for patients failing medical therapy or developing complications (perforation, massive hemorrhage, toxic megacolon). 8, 6

Surgical Intervention

Subtotal colectomy with ileostomy and rectosigmoid mucous fistula is the procedure of choice in emergency settings, minimizing septic complications while preserving options for future intestinal continuity restoration. 8

Approximately 20% of ASUC patients require colectomy during the same admission, with risk increasing after subsequent episodes. 1

Special Considerations

Older patients and frailty:

• Older patients with comorbidities and frailty have worse outcomes
• Avoid unnecessarily prolonged steroid courses in frail patients
• Consider adjunctive measures like hyperbaric oxygen therapy or total enteral nutrition given favorable safety profiles 7

Patients already on advanced therapy:

• New 2026 consensus criteria suggest modified thresholds for patients already receiving corticosteroids or biologics (CRP ≥1× ULN for those on high-dose steroids, ≥2× ULN for those on advanced therapy) 9