Decision support only — involve the IBD team and colorectal surgery early for severe colitis, obstruction, abscess or perianal sepsis. Exclude infection before escalating immunosuppression and use current Australian PBS criteria.
1 Phenotype, severity, complication: all three drive treatment
Mild, uncomplicatedambulatory; limited systemic effect
UC: mild bleeding/urgency, limited endoscopic activity. Crohn: low inflammatory burden, no deep ulceration, stricture, penetrating or perianal disease.
Use disease-specific local therapy: optimised oral/rectal 5-ASA for UC; budesonide for selected ileocaecal Crohn. Define a response date.
Moderate–severe / high risksteroid need, deep disease, poor prognostic features
Frequent symptoms, anaemia/weight loss, raised CRP/calprotectin, ulcers, extensive or proximal Crohn, perianal disease, prior admission/surgery.
Induce promptly and plan steroid-free maintenance. Early advanced therapy often makes more sense than cycling steroids/thiopurine alone. ECCO/GESA
Acute severe UC≥6 bloody stools/day + systemic toxicity
Truelove–Witts: tachycardia, fever, Hb <105 g/L, ESR >30 or CRP >30. Admit under gastro + colorectal surgery.
IV steroid, LMWH, stool infection screen and flexible sigmoidoscopy. Assess response on day 3; rescue or colectomy must not drift. ECCO 2026
Crohn complicationsepsis, obstruction, perforation, haemorrhage
Abscess/phlegmon, peritonism, complete obstruction, toxic dilation, fistula with sepsis, uncontrolled bleeding or nutritional failure.
Source control and surgical pathway first. Steroid escalation into an undrained abscess is a bad trade.
Symptoms alone are unreliable: IBS, bile-acid diarrhoea, infection, SIBO and fixed fibrostenosis can all mimic inflammatory activity. Escalate against objective evidence.
2 Bloody diarrhoea: diagnose before labelling IBD
Use one combined pathway until infection, ischaemia and other mimics have been addressed. Crohn disease versus ulcerative colitis is an endoscopic, histological and imaging conclusion, not a guess from stool appearance.
VISIBLE BLOOD + DIARRHOEA
Confirm that blood is rectal rather than melaena, haematuria or menstrual. Record onset, stool frequency, nocturnal symptoms, urgency/tenesmus, pain, fever, weight loss and volume depletion.
First gate: unstable, peritonitic or severe colitis?
YES — RESUSCITATE + ADMIT
Red flags: shock/syncope, major Hb fall, dehydration/AKI, severe abdominal pain or pain out of proportion, guarding/distension, fever/sepsis, toxic dilation, or ≥6 bloody stools/day with systemic toxicity.
Now: IV access, fluids/blood as required; FBC, UEC, LFT/albumin, CRP, coagulation, group-and-screen ± lactate/blood cultures. CT abdomen/pelvis with IV contrast for acute abdomen, suspected ischaemia or Crohn complication; AXR if toxic megacolon is possible. Gastroenterology + colorectal surgery early.
NO — FOCUSED HISTORY + EXAM
Infection: travel, food/water, sick contacts/outbreak, antibiotics or admission, animal exposure. IBD: chronicity, prior episodes, family history, oral/eye/joint/skin or perianal disease.
Mimics: vascular disease/hypoperfusion and sudden pain; NSAIDs, mycophenolate or checkpoint inhibitors; radiation, diverticular disease or cancer. Ask about receptive anal sex/STI risk when proctitis is plausible.
Test all clinically significant bloody diarrhoea
FBC, UEC, CRP, LFT/albumin ± ferritin/TSAT. Send diarrhoeal stool for local enteric PCR/culture including Salmonella, Shigella, Campylobacter, Yersinia and STEC/Shiga toxin, plus C. difficile. Add ova/parasites and Entamoeba histolytica testing for travel, exposure, immunocompromise or ≥14-day illness. Faecal calprotectin supports intestinal inflammation but does not distinguish IBD from infection.
Pathogen or another convincing alternative found?
YES — TREAT THE CAUSE
Infection: use organism-specific and local public-health guidance. Routine empirical antibiotics are usually avoided in immunocompetent adults while results are pending. If STEC is possible, avoid antimotility drugs and antibiotics until clarified; monitor Hb, platelets and creatinine if HUS is a concern. Sepsis or severe immunocompromise is a different pathway.
Ischaemia / surgical pathology: urgent imaging and gastro/surgical review. Persistent bleeding or inflammatory features after an infection resolves still need reassessment; a positive multiplex PCR can represent carriage or coinfection.
NO / PERSISTENT SUSPICION — ENDOSCOPY
Stable: ileocolonoscopy with terminal ileal intubation and segmental biopsies from abnormal and normal-appearing mucosa. Acute severe colitis: limited unprepared flexible sigmoidoscopy with biopsies; defer full colonoscopy until safer.
Map beyond the mucosa: intestinal ultrasound and/or MRE when Crohn disease is suspected; CT when an acute complication needs speed; MRI pelvis for perianal fistula/abscess. Capsule follows a negative ileocolonoscopy only after stenosis/retention risk is addressed.
UC PATTERN
Continuous mucosal inflammation from the rectum proximally; severity and extent vary. Histology usually supports chronic colitis, although very early disease can be less definite. Infection can look identical endoscopically.
CROHN PATTERN
Skip/segmental disease, terminal ileum or upper GI involvement, deep linear/aphthous ulcers, stricturing, fistulising or perianal disease. Complete small-bowel assessment.
IBD-U / OTHER
If clinical, imaging, endoscopic and histological findings disagree, use IBD-unclassified and review the differential. Do not force a UC/Crohn label from one test or a single biopsy.
Do not wait for faecal calprotectin in significant visible bleeding or severe illness. It is a triage and monitoring marker, not a pathogen test or a substitute for endoscopy.
Before calling it a flare
- StoolC. difficile testing and culture/multiplex panel as exposure suggests; parasites if travel/risk. Do this before steroids where feasible.
- BloodFBC, CRP/ESR, UEC, LFT/albumin, ferritin/TSAT; B12/folate/vitamin D when relevant. Blood cultures if septic.
- CalprotectinUseful for gut inflammation and serial response, but not specific for IBD; infection, NSAIDs and cancer can raise it.
Establish phenotype
- PatternUC is continuous mucosal colitis extending proximally from the rectum. Crohn disease is patchy and transmural anywhere from mouth to anus; strictures, fistulae and abscesses change the treatment pathway. Surgery is not curative for Crohn disease.
- EndoscopyIleocolonoscopy with segmental biopsies from inflamed and normal-appearing mucosa. Histology helps exclude infection and mimicry.
- Small bowelMRE or intestinal ultrasound; CT enterography when speed/availability wins. Capsule only after obstructive risk is excluded.
- PerianalExamine; MRI pelvis ± examination under anaesthesia for suspected complex fistula/abscess.
Mimics and associated disease
- MimicsInfectious, ischaemic, drug/NSAID, microscopic, diverticular or immune-checkpoint colitis; Behçet, intestinal TB and endometriosis.
- CMVBiopsy ulcer bases in severe/steroid-refractory colitis; blood PCR alone neither proves nor excludes tissue-invasive colitis.
- PSCPersistent cholestatic liver tests, pruritus or biliary features → hepatology and MRCP. PSC changes colorectal and hepatobiliary cancer surveillance.
- SerologypANCA/ASCA do not replace endoscopy, histology and imaging.
3 Ulcerative colitis: induction and maintenance
| Setting | Induction | Maintenance / escalation |
|---|
| Proctitis | Mesalazine suppository 1 g daily is preferred; add oral 5-ASA if response is incomplete or symptoms extend proximally. ECCO 2026 | Continue the effective rectal ± oral 5-ASA regimen. Adherence and delivery matter more than brand. |
| Left-sided mild–moderate | Mesalazine enema or foam ≥1 g/day plus oral mesalazine ≥2 g/day. Combined treatment is generally more effective than either route alone. ECCO 2026 | Oral ± rectal 5-ASA. Choose a rectal formulation the patient will actually use. |
| Extensive mild–moderate | Oral mesalazine ≥2 g/day; add rectal mesalazine ≥1 g/day for induction, particularly with distal symptoms. Once-daily oral dosing is acceptable. ECCO 2026 | Oral ± rectal 5-ASA. If optimised 5-ASA fails: budesonide MMX 9 mg daily or systemic steroid, then reassess phenotype, adherence and inflammatory activity. |
| Moderate–severe / steroid-dependent | Short systemic corticosteroid bridge or advanced therapy selected by speed, prior exposure, EIMs, pregnancy plans, infection/VTE/cardiac/malignancy risk and patient preference. | Anti-TNF, vedolizumab, ustekinumab, JAK inhibitor or S1P modulator according to PBS/specialist plan. No steroid maintenance. |
| After response to rescue | Infliximab or ciclosporin pathway in ASUC. | Continue infliximab if it induced response; after ciclosporin, bridge to thiopurine or another durable advanced therapy chosen by the IBD team. |
Which 5-ASA?
- MesalazineUsually preferred: similar efficacy with better tolerability than sulfasalazine. Oral, suppository, foam and enema formulations are PBS-listed; match delivery to disease extent.
- SulfasalazineA reasonable lower-cost alternative when tolerated. More nausea, headache, rash/hypersensitivity and reversible oligospermia; consider folate and monitor FBC/LFT/renal function. Rare interstitial nephritis is a 5-ASA class concern, not a sulfasalazine-only toxicity.
Coexisting arthritis: do not overstate it
Sulfasalazine may help peripheral enteropathic arthritis and can be considered when it also suits the colitis. It is not a reliable treatment for axial spondyloarthritis. Define the joint phenotype and involve rheumatology rather than calling it the universal “drug of choice”. ECCO EIM 2024
4 Crohn disease: location and behaviour matter
Luminal disease
- IleocaecalBudesonide 9 mg daily for mild–moderate localised inflammatory disease. It will not fix a fibrotic stricture.
- More severeSystemic corticosteroid can induce; start a steroid-sparing plan at the same time. Thiopurines and methotrexate are too slow for induction.
- AdvancedAnti-TNF, vedolizumab, ustekinumab, upadacitinib and other PBS-listed agents are chosen by phenotype and prior exposure. Combination infliximab + thiopurine can reduce immunogenicity. SONIC
- 5-ASADo not extrapolate UC treatment. Mesalazine has little useful efficacy for active Crohn disease.
Complicated disease
- AbscessAntibiotics + image-guided/surgical drainage where feasible; delay/intentionally sequence immunosuppression until sepsis is controlled.
- ObstructionIV fluid/electrolytes, bowel rest ± NG, cross-sectional imaging and early surgery. Steroids only when inflammatory narrowing is likely and sepsis/perforation excluded.
- PerianalDrain abscess, place seton for complex fistula, then combined medical–surgical care. Infliximab has the strongest RCT evidence; antibiotics are adjuncts.
- Post-opRisk-stratify and prevent recurrence; ileocolonoscopy at 6–12 months, with therapy adjusted to Rutgeerts/endoscopic activity.
5 Acute severe ulcerative colitis: a timed pathway
| When | Do | Decision |
|---|
| Admission / day 0 | Gastro + colorectal surgery; AXR/CT if dilation or complication; stool C. difficile/culture; FBC, CRP, UEC, LFT/albumin; flexible sigmoidoscopy with biopsies within ~24 h. Give LMWH prophylaxis and nutrition. | Start methylprednisolone 60 mg IV daily or hydrocortisone 100 mg IV 3–4 times/day. Avoid opioids, anticholinergics, loperamide and routine antibiotics/TPN. ACG 2025/ECCO 2026 |
| Daily | Stool frequency/blood, vitals, abdominal exam, FBC/CRP/electrolytes/albumin; repeat imaging if dilation or deterioration. | Perforation, toxic megacolon, uncontrolled haemorrhage or worsening systemic toxicity → urgent colectomy, not another drug trial. |
| Day 3 | Objective steroid response. Oxford criterion: >8 stools/day, or 3–8 plus CRP >45 mg/L, predicts high colectomy risk in the original cohort. | If inadequate: infliximab or IV ciclosporin rescue, chosen with surgical and patient factors. Routine initial infliximab 10 mg/kg or accelerated dosing has not improved major outcomes; individualise only in an expert pathway. ECCO 2026 |
| After rescue failure | Reassess sepsis/CMV, drug exposure and surgical timing. | Colectomy is standard. Sequential third-line infliximab/calcineurin/JAK rescue is only for highly selected patients in an expert MDT after explicit risk discussion. ECCO 2026 |
6 Advanced therapy: safe setup, then objective follow-up
Australian PBS indication matrix from the GESA IBD Faculty cheat sheet, effective 1 July 2026. A tick means a PBS authority pathway exists for that indication; it does not rank efficacy or replace phenotype-based selection.
| Class / medicine | Moderate–severe UC | Severe luminal Crohn | Fistulising Crohn | Practical point |
|---|
Adalimumab / infliximab
anti-TNF | PBS | PBS | PBS | Infliximab has the strongest trial evidence for complex fistulising disease; drain sepsis and combine medical–surgical care. |
Golimumab
anti-TNF | PBS | — | — | UC pathway only. |
Vedolizumab
anti-integrin | PBS | PBS | — | Gut-selective; may not control systemic extraintestinal inflammation. |
Ustekinumab
IL-12/23 | PBS | PBS | PBS | Authority item and induction/maintenance formulation differ. |
Upadacitinib
JAK inhibitor | PBS | PBS | — | Fast oral option; screen infection and assess VTE/MACE, malignancy and reproductive risk. |
Tofacitinib
JAK inhibitor | PBS | — | — | UC pathway only; class cautions apply. |
Ozanimod / etrasimod
S1P modulators | PBS | — | — | UC pathways only; check cardiac, ophthalmic, hepatic, infection and interaction issues. |
PBS authority is part of the prescription
Initial, change/recommencement, balance and continuing criteria are indication-specific. Record disease severity, prior therapy and objective response. Online authority is available for GESA-listed severe luminal and fistulising Crohn pathways; use the live PBS item and GESA sheet at the point of prescribing because codes, brands and repeats change.
Before the first dose
- InfectionTB screen; HBsAg/anti-HBc/anti-HBs; HCV/HIV by risk; varicella status; dental/skin focus where relevant.
- VaccinesInfluenza, COVID, pneumococcal, HBV, HPV and recombinant zoster as indicated. Give live vaccines before immunosuppression; avoid during significant immunosuppression.
- ThiopurineTPMT ± NUDT15 by local practice, then baseline FBC/LFT. Counsel pancreatitis, infection and lymphoma/non-melanoma skin-cancer risk; use the local laboratory-monitoring schedule.
- RiskMalignancy history, VTE/MACE, pregnancy, heart failure/demyelination, cytopenia, liver/renal function and drug interactions.
Choose deliberately
- Need speedAnti-TNF or JAK inhibitor can act quickly; JAK/S1P agents have specific thrombotic, cardiac, lipid, infection and reproductive cautions.
- EIMsArthritis, psoriasis, uveitis and perianal disease may favour systemic agents; gut-selective vedolizumab may not treat extraintestinal inflammation.
- PBSEligibility and continuation require documented severity and response. Check the indication matrix above, then confirm the live authority item and local biologic protocol.
Treat to target
- EarlySymptoms and CRP/calprotectin after induction. Confirm adherence before declaring mechanistic failure.
- ObjectiveEndoscopy, intestinal ultrasound or MRE to document healing/response. ECCO 2025 gives IUS a larger first-line monitoring role.
- LossFor anti-TNF loss of response, reactive trough/antibody testing can separate underexposure, immunogenicity and mechanistic failure.
7 Health maintenance, pregnancy and cancer surveillance
Risk-stratify after the baseline surveillance examination and revisit the interval after every colonoscopy. Australian guidance remains the local default below; the newer BSG 2025 pathway is shown separately because it has not been formally adopted in Australia.
Who enters colitis surveillance?
- BaselineColonic IBD: risk-assessment colonoscopy 8 years after symptom onset, ideally in remission. This includes UC beyond isolated proctitis and Crohn colitis involving at least one-third of the colon.
- PSCBegin at PSC diagnosis and perform annually, including after liver transplantation. PSC-associated colitis can be clinically quiet.
- Not IBD surveillanceIsolated ulcerative proctitis, isolated small-bowel/ileal Crohn disease, or Crohn disease confined to the rectum: use the age-appropriate Australian population screening pathway unless another indication exists.
- ReassessInflammatory burden, extent, PSC, stricture, post-inflammatory polyps, dysplasia and family history can change. Recalculate after each examination and at least annually in clinic.
Australian interval — Cancer Council / NHMRC
- Every yearAny high-risk feature: PSC; ongoing chronic active inflammation; prior colorectal dysplasia; colonic stricture; pseudopolyps or a foreshortened tubular colon; first-degree relative with CRC diagnosed at ≤50 years.
- Every 3 yearsIntermediate: quiescent disease with no high-risk feature and no first-degree relative with CRC. This is the practical default until repeated examinations establish a low-risk course.
- Every 5 yearsLow risk: quiescent disease, no other risk factors and inactive disease on consecutive surveillance colonoscopies.
- OverrideKnown dysplasia, incomplete resection or a separate familial/polyp-surveillance indication may require a shorter interval or surgery; use the dysplasia MDT pathway.
BSG 2025 — newer international alternative
| Risk after optimised treatment | Suggested action |
|---|
| Severe persistent endoscopic or histological inflammation | Discuss colectomy, or use an individualised multivariable risk estimate; surveillance alone may be the wrong answer. |
| Moderate active inflammation, dysplasia, PSC or colonic stricture | Annual colonoscopy |
| Mild active inflammation; extensive disease (UC proximal to the splenic flexure, or Crohn colitis affecting >50% of the colon / ≥3 segments); post-inflammatory polyps; or CRC in any first-degree relative | Every 3 years |
| No additional risk factor / close to population risk | Age-appropriate population bowel-cancer screening plus colonoscopic reassessment every 10 years. Re-enter 1- or 3-year surveillance if risk changes. |
| Domain | Action | High-yield detail |
|---|
| CRC technique / dysplasia | Perform surveillance in remission with high-definition colonoscopy; dye-spray chromoendoscopy is preferred where expertise is available. Carefully inspect and target visible lesions. | Visible, clearly resectable dysplasia → expert complete resection plus risk-based follow-up. Invisible, multifocal, incompletely resected or high-grade dysplasia → repeat expert examination and IBD dysplasia MDT; colectomy may be appropriate. |
| Pregnancy | Aim for remission before conception; active disease is often the larger fetal risk. Continue effective pregnancy-compatible therapy with IBD/obstetric input. | Methotrexate is contraindicated. JAK/S1P and newer agents require product-specific advice. Most biologics are continued when needed; plan infant live vaccines after in-utero exposure. |
| Nutrition / bone / iron | Dietitian; iron studies and replacement; B12 after ileal disease/resection; vitamin D/calcium; DEXA for steroid, malnutrition and other risk. | Exclusive enteral nutrition is effective Crohn induction, especially in children; restrictive diets need supervision. No diet is proven to induce UC remission. |
| General prevention | Smoking cessation (especially Crohn), cervical screening, skin protection/exam by risk, anxiety/depression and sexual-health care. | Avoid NSAIDs when they trigger disease; check VTE prophylaxis for every IBD admission, even with rectal bleeding unless contraindicated. |
Primary sources. GESA clinical practice resources, including the
IBD Faculty PBS Cheat Sheet effective 1 Jul 2026 and
Advanced Therapies Prescription Guide;
PBS mesalazine formulations and
PBS sulfasalazine items;
ECCO–ESGAR–ESP–IBUS diagnostics/monitoring 2025;
RCPA Manual: diarrhoea;
IDSA infectious diarrhoea guideline; ECCO Crohn therapeutics 2024;
ECCO UC therapeutics 2026;
ECCO extraintestinal manifestations 2024; ACG UC 2025;
BSG adult IBD guideline 2025;
Cancer Council Australia/NHMRC surveillance-colonoscopy guideline;
BSG colorectal surveillance in IBD 2025; STRIDE-II.
Key trials. SONIC (infliximab/azathioprine), SUCCESS (UC combination therapy), ACT 1/2, GEMINI, UNIFI, SELECTION and pivotal JAK/S1P trials; CYSIF and CONSTRUCT (infliximab vs ciclosporin in ASUC).
Caveats. PBS eligibility and dosing change often; matrix checked against the GESA workbook on 6 Sep 2026. Australian CRC intervals derive from an NHMRC-approved guideline whose underlying evidence review predates BSG 2025; the BSG scheme is shown as a contemporary alternative, not as adopted Australian policy. A PBS listing is not evidence of clinical efficacy for every phenotype: in particular, do not use 5-ASA as routine active Crohn therapy. Multiplex stool panels detect nucleic acid and require clinical interpretation; local panels and public-health requirements differ. Oxford day-3 performance is weaker in some modern cohorts; use it as a prompt for a timed MDT decision, not a solitary colectomy order. Verify local CMV, therapeutic-drug-monitoring and perioperative protocols.