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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Acute severe ulcerative colitis

Gastroenterology and hepatology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull

Overview

Recognise acute severe ulcerative colitis on admission, deliver a time-critical inpatient bundle, and decide rescue therapy or colectomy before physiological deterioration removes safer options.

ASUC is a distinct high-risk state, not simply a bad outpatient flare. The classic definition combines frequent bloody stool with fever, tachycardia, anaemia or raised inflammatory activity. Patients can deteriorate from inflammation, blood loss, dehydration, electrolyte disturbance, sepsis, thrombosis or colonic dilatation. The first 24 hours should establish diagnosis and complications while treatment begins. A plain abdominal radiograph can rapidly show colonic diameter and stool pattern; CT is reserved for suspected perforation, abscess or an alternative diagnosis because routine repeated CT adds radiation and transport risk.

Intravenous corticosteroid remains initial treatment for most patients after stool specimens are collected, but response must be time-limited. The Oxford day-three index, using stool frequency and CRP, helps identify a high chance of corticosteroid failure, although trajectory, radiology, albumin and overall physiology also matter. Rescue infliximab or ciclosporin is chosen from prior biologic exposure, albumin and inflammatory burden, comorbidity, infection risk, drug monitoring capability, patient preference and local expertise. A patient who requires surgery should reach theatre resuscitated and informed rather than after perforation or multiorgan failure.

Key points

  • Acute severe ulcerative colitis is conventionally defined by at least six bloody stools daily plus systemic disturbance using Truelove and Witts features; it is a medical and surgical emergency.
  • Admit under gastroenterology with colorectal surgical involvement from the start, because early discussion improves planning and does not commit the patient to colectomy.
  • Send stool culture and Clostridioides difficile testing, perform blood and abdominal assessment, and undertake careful limited sigmoidoscopy with biopsies for severity and cytomegalovirus when relevant.
  • Start intravenous corticosteroid promptly after cultures, while providing fluids, electrolyte correction, nutrition, pharmacological thromboprophylaxis and avoidance of antimotility medicines and unnecessary opioids.
  • Record stool number and blood, observations, abdominal signs, CRP, blood count, albumin and renal function daily; vague better or worse language is unsafe.
  • At day three, more than 8 bowel movements daily, or 3–8 daily with CRP above 45 mg/L, predicts a high risk of corticosteroid failure; make the multidisciplinary decision between rescue infliximab, rescue ciclosporin and colectomy without delay.
  • Do not give sequential rescue therapies casually because cumulative immunosuppression can increase infection and delay surgery; exceptional use belongs in a highly experienced service.

Aetiology

01

Severe uncontrolled colitis

Extensive ulcerative colitis can escalate into high-burden mucosal inflammation, sometimes at first presentation or after inadequate response to maintenance therapy.

02

Infectious contribution

Clostridioides difficile and, in selected immunosuppressed patients, cytomegalovirus can trigger, mimic or compound a severe flare and therefore warrants active assessment.

03

Treatment interruption or failure

Non-adherence, interrupted immunosuppression, corticosteroid dependence or loss of response to established therapy may precede deterioration, although a precipitant may remain unidentified.

Pathophysiology

  1. 1
    Diffuse mucosal inflammation

    Intense continuous colonic inflammation causes friability, ulceration, bleeding and impaired absorption across a large mucosal surface.

  2. 2
    Systemic and nutritional loss

    Frequent bloody stool causes fluid, electrolyte, protein and blood loss while inflammatory cytokines drive fever, tachycardia and catabolism.

  3. 3
    Neuromuscular failure

    Deepening inflammation can impair colonic smooth muscle and neural function, producing dilatation, toxic megacolon, ischaemia and eventual perforation.

Clinical features and red flags

Severe-colitis threshold

Six or more bloody stools per day plus systemic disturbance such as tachycardia, fever, anaemia or marked inflammatory response should trigger the formal ASUC pathway.

Toxic megacolon

Colonic dilatation with systemic toxicity, increasing distension, tenderness, fever, tachycardia, altered consciousness or falling stool output signals dangerous neuromuscular failure and perforation risk.

Steroid non-response

Persistent frequent bloody stool and inflammatory response by day three, worsening pain, falling albumin or radiographic deterioration argues against prolonged corticosteroid monotherapy.

Concurrent infection

C. difficile or cytomegalovirus can worsen established UC; infection does not automatically exclude active inflammation and both components may need coordinated treatment.

Impending physiological failure

Hypotension, oliguria, rising lactate, worsening anaemia, confusion or respiratory compromise indicates that routine rescue deliberation must give way to resuscitation and urgent surgery assessment.

Thromboembolic complication

New pleuritic pain, hypoxaemia, unilateral swelling, abdominal pain or neurological deficit may represent venous or arterial thrombosis in a highly prothrombotic inflammatory admission.

Red flags requiring action

  • Free perforation, peritonism, uncontrolled major haemorrhage or toxic megacolon with deterioration is an indication for emergency surgical management, not further rescue escalation.

Investigations

  1. 01
    Daily full blood count, CRP, albumin, renal and electrolyte profileFirst step
    Why
    Track inflammatory burden, bleeding, nutrition, renal perfusion and correction needs.
    Interpretation and limitations
    Use trends with stool count and physiology; falling CRP after rescue is encouraging only if the abdominal and systemic state also improves.
  2. 02
    Stool culture and C. difficile assay
    Why
    Identify enteric infection that changes antimicrobial, isolation and immunosuppression decisions.
    Interpretation and limitations
    Collect before antimicrobials when feasible but do not delay resuscitation; a detected pathogen can coexist with severe UC and requires joint specialist management.
  3. 03
    Abdominal radiograph
    Why
    Assess colonic dilatation, mucosal islands and stool distribution at low procedural burden.
    Interpretation and limitations
    Dilatation or increasing gas with toxicity heightens surgical urgency, while a normal initial film does not exclude later deterioration and should be repeated only when clinically indicated.
  4. 04
    Unprepared limited flexible sigmoidoscopy
    Why
    Confirm severe active colitis and obtain biopsies without full-colon instrumentation.
    Interpretation and limitations
    Describe deep ulceration and collect tissue for histology and cytomegalovirus assessment where appropriate; minimise insufflation and avoid traversing a dangerously inflamed colon.

Differential diagnosis

01

Infectious colitis

Positive stool testing, exposure history or toxin detection supports enteric infection, but infection and active ulcerative colitis can coexist and require parallel management.

02

Crohn or indeterminate colitis

Skip lesions, small-bowel or perianal disease and transmural features favour Crohn disease, although severe treated colitis may obscure the usual distribution.

03

Ischaemic colitis

Abrupt pain followed by bleeding, vascular or low-flow risk and a segmental watershed pattern favour ischaemia over a conventional inflammatory flare.

Management

01ADMITDeliver the first-day bundleFirst stepBloody stool frequency and systemic features meet or strongly suggest acute severe ulcerative colitis.+
  1. 1Admit to a specialist-capable ward, notify gastroenterology and colorectal surgery, perform ABCDE assessment and document abdominal examination and treatment ceiling.
  2. 2Send blood, stool culture and C. difficile tests, obtain an abdominal radiograph and arrange limited sigmoidoscopy with biopsies when stable enough.
  3. 3Begin protocolised intravenous corticosteroid, fluids and electrolyte correction, nutrition assessment and pharmacological venous-thromboembolism prophylaxis unless a true contraindication exists.
  4. 4EscalationStop antimotility drugs, unnecessary NSAIDs and avoid escalating opioids; treat proven infection and provide clear daily multidisciplinary review.

Complications

01

Toxic megacolon and perforation

Severe inflammation can produce non-obstructive dilatation, systemic toxicity, mural necrosis and perforation requiring urgent colectomy or emergency colectomy.

02

Venous thromboembolism

Active inflammation, immobility, dehydration and corticosteroid exposure markedly increase thrombosis risk even when rectal bleeding is present.

03

Anaemia and malnutrition

Ongoing blood, protein and electrolyte loss with reduced intake causes anaemia, hypoalbuminaemia, sarcopenia and poorer resilience for rescue therapy or surgery.

Monitoring and follow-up

  • Chart total and bloody stools separately each day, alongside pulse, temperature, blood pressure, urine output, abdominal distension and tenderness.
  • Trend CRP, full blood count, albumin, electrolytes and renal function daily, replacing potassium, magnesium and phosphate safely as needed.
  • Repeat abdominal imaging when distension, pain, systemic toxicity or reduced stool passage suggests developing megacolon or perforation.
  • During rescue, perform agent-specific infection, renal, blood pressure, magnesium, cholesterol, infusion and drug-concentration monitoring according to protocol.
  • Document a daily joint gastroenterology-surgery decision, including response, rescue clock, operative trigger and what has been explained to the patient.
  • After discharge or colectomy, ensure corticosteroid taper, thrombosis advice, nutrition, stoma or maintenance therapy and rapid-access follow-up are explicitly handed over.

Special situations

Surgical review is not defeat

Early colorectal involvement preserves time for explanation, stoma marking and optimisation. It does not prevent successful medical rescue when response is adequate.

Day three is a decision point

The Oxford index identifies high corticosteroid-failure risk; its value is prompting action while the patient is stable enough to choose safely.

Less stool can be worse

When a toxic inflamed colon dilates and loses motility, stool frequency may fall even as perforation risk rises. Always pair the chart with examination.

Thrombosis prevention still matters

Inflammation and immobility create substantial thrombotic risk. Controlled rectal bleeding is not the same as a prohibitive haemorrhage contraindication to prophylaxis.

Rescue needs an exit

Before infliximab or ciclosporin, define the response window, maintenance strategy and surgical threshold so a transient biochemical change cannot create indefinite delay.

Common pitfalls

  1. 01

    Managing ASUC as an outpatient flare and losing the window for safe rescue or planned surgery.

  2. 02

    Waiting for every infection result before beginning intravenous corticosteroid in a stable patient after specimens are collected.

  3. 03

    Using opioids, anticholinergics or antimotility medicines that can obscure deterioration and worsen colonic dilatation.

  4. 04

    Continuing steroids beyond day three without a documented rescue or operative decision despite objective non-response.

  5. 05

    Interpreting a lower stool count as improvement when abdominal distension and systemic toxicity are worsening.

  6. 06

    Giving sequential ciclosporin and infliximab routinely without accounting for cumulative immunosuppression and surgical delay.

  7. 07

    Withholding all thromboprophylaxis solely because inflammatory rectal bleeding is visible.

Practice

Two practice questions

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Question 1 of 2
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Gastroenterology and hepatologyOriginal SBA

Day-three non-response

A patient with ASUC has received appropriate intravenous corticosteroid for three days. Bloody stool frequency remains high and CRP is markedly raised, but there is no perforation. What is the best next step?

Choose one answer, then submit
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Sources and review status5 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • British Society of Gastroenterology guidelines on inflammatory bowel disease in adults: 2025Current UK ASUC definition, investigations, intravenous corticosteroid regimens, day-three response assessment, rescue therapy and surgical timing.
  • NICE NG130 Ulcerative colitis recommendationsHospital treatment, rescue therapy and surgical principles.
  • ACPGBI Acute severe colitis resourceBritish colorectal specialist guidance and operative context.
  • IBD UK Standards 2026 inpatient careSpecialist inpatient review and coordinated discharge expectations.
  • Infliximab UK SmPCLicensed administration, contraindications and major safety risks.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
  • Perforation, uncontrolled haemorrhage, toxic megacolon or continuing deterioration despite optimal rescue requires urgent colectomy rather than repeated medical delay.
    • Reduced stool frequency with increasing distension and systemic toxicity can mean colonic paralysis rather than improvement.
  • Do not delay colectomy because CRP temporarily falls if pain, tenderness, dilatation, haemodynamics or organ function are worsening.
  • Fever, shock or new organ dysfunction during combined immunosuppression requires immediate sepsis assessment and source control.
  • Hypokalaemia, hypomagnesaemia, anaemia and malnutrition amplify ileus, arrhythmia and operative risk and require active correction.
  • 05
    Oxford day-three assessment
    Why
    Estimate likelihood that intravenous corticosteroid alone will fail.
    Interpretation and limitations
    At day three, more than 8 bowel movements daily, or 3–8 daily with CRP above 45 mg/L, predicts a high likelihood of corticosteroid failure and colectomy; use it to trigger the rescue-or-surgery decision, not postpone one.
  • 06
    Pre-rescue infection and safety screen
    Why
    Identify contraindications and practical risk before infliximab or ciclosporin.
    Interpretation and limitations
    Review chest imaging, hepatitis, tuberculosis status, renal function, magnesium, cholesterol, blood pressure, vaccination and prior biologic exposure according to the candidate agent and urgency.
    • 02DAY 3Make a rescue or surgery decisionAfter approximately three days of intravenous corticosteroid, response is incomplete or clinical concern persists.+
    1. 1Count bloody and total stools accurately and review CRP, haemoglobin, albumin, observations, examination and radiology, applying the Oxford index as decision support.
    2. 2Exclude new sepsis, C. difficile, cytomegalovirus concern and developing dilatation or perforation before choosing more immunosuppression.
    3. 3Discuss infliximab, ciclosporin and colectomy together with the patient, gastroenterologist and colorectal surgeon, incorporating prior drug exposure and local expertise.
    4. 4Select one rescue strategy with a predefined response window and surgical trigger, or proceed directly to colectomy when physiology or patient preference makes rescue inappropriate.
    03RESCUEMonitor one selected rescue therapySteroid-refractory ASUC remains medically salvageable without perforation, uncontrolled bleeding or toxic deterioration.+
    1. 1Administer specialist infliximab or ciclosporin using the local ASUC protocol, documenting dosing rationale, contraindications and intended maintenance bridge.
    2. 2Continue objective daily stool, blood, abdominal and biochemical review while maintaining surgical readiness rather than interpreting drug administration as resolution.
    3. 3Recognise altered pharmacokinetics in severe inflammation and low albumin, using specialist drug-level or accelerated strategies only within experienced protocols.
    4. 4Proceed to surgery promptly when the agreed response is not achieved or any emergency indication develops; avoid unplanned sequential rescue.
    04SURGERYPrepare timely subtotal colectomyMedical treatment fails, rescue is contraindicated, or haemorrhage, perforation, megacolon or deterioration mandates operation.+
    1. 1Resuscitate with blood products, fluids, electrolytes, antibiotics when indicated and thrombosis planning while avoiding delay for non-essential tests.
    2. 2Explain that emergency subtotal colectomy with end ileostomy and retained rectal stump is commonly the safest staged approach, with reconstructive choices considered after recovery.
    3. 3Involve stoma specialists, anaesthesia, nutrition and critical care early, acknowledging that an emergency may limit but should not eliminate patient information.
    4. 4After surgery, taper corticosteroid safely, monitor the rectal stump and stoma, and plan rehabilitation plus later completion or pouch discussion.
    Key medicines and prescribing safety4 treatments · regimens, roles and cautions+
    First-line anti-inflammatory treatment for most patients while infection tests and early outcome assessment proceed.

    Intravenous corticosteroid

    Give either methylprednisolone 30 mg intravenously every 12 hours or hydrocortisone 100 mg intravenously every 6 hours under the inpatient ASUC protocol. Record response daily and make the formal rescue-or-surgery decision after at least 3 days; higher corticosteroid doses do not add benefit and prolonged ineffective treatment must not delay colectomy.

    Check glucose, mental state and infection; benefit should be judged by day three and treatment must not continue ineffectively while surgery is delayed.

    TNF blockade can rescue corticosteroid-refractory ASUC and provide a maintenance pathway in selected patients.

    Infliximab rescue

    Use infliximab 5 mg/kg by intravenous infusion as specialist rescue after at least 3 days of intravenous corticosteroid without adequate response. Confirm the named product and infusion schedule through the inpatient IBD service; consider intensified dosing only in a selected high-clearance phenotype, particularly low albumin, and do not combine or casually sequence it with ciclosporin.

    Avoid uncontrolled sepsis; low albumin and high inflammatory clearance may affect exposure, while tuberculosis, hepatitis, infusion reaction and postoperative infection risk require specialist judgement.

    Calcineurin inhibition offers rapid rescue, usually as a bridge to a sustainable maintenance treatment.

    Intravenous ciclosporin rescue

    Use ciclosporin 2 mg/kg/day by continuous intravenous infusion as specialist rescue after at least 3 days of intravenous corticosteroid without adequate response, with therapeutic drug, renal, blood-pressure, electrolyte and interaction monitoring. Define the approximately 1-week intravenous course and oral or maintenance bridge through the experienced inpatient IBD service; do not combine or casually sequence it with infliximab.

    Renal impairment, hypertension, low magnesium, seizures, infection and major interactions require close surveillance; the discharge bridge must be planned before initiation.

    Reduces the high venous-thromboembolism risk associated with severe active colitis and hospitalisation.

    Low-molecular-weight heparin prophylaxis

    Prophylactic inpatient regimen adjusted for renal function, weight and bleeding contraindications.

    Rectal bleeding alone is not automatically a contraindication, but haemodynamic haemorrhage, thrombocytopenia and renal impairment need senior individual review.