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Crohn's Disease

NICE guideline [NG129] Crohn's disease: management. Published: May 2019. NICE Clinical guideline [CG118] Colorectal cancer prevention: colonoscopic surveillance in adults with ulcerative colitis, Crohn's disease or adenomas. Last updated: Sep 2022. NICE CKS Crohn's disease. Last revised: May 2024.

Guidelines

NICE CKS recommends the following tests when Crohn's disease is suspected. There are 2 main purposes of the following tests: 1) support diagnosis of inflammatory bowel disease and 2) exclude differential diagnoses.
 
Category Test Purpose / Interpretation
Blood tests FBC
  • Anaemia is common at diagnosis, supports malabsorption, malnutrition, GI bleed
  • ↑ Platelet count suggests inflammation
U&E  
LFT, including albumin
  • ↓ Albumin may indicate inflammation and malnutrition, or possible protein-losing enteropathy
Serum ferritin, vitamin B12, folate, vitamin D
  • Detect nutritional deficiencies due to malabsorption
Inflammatory markers (CRP and ESR)
  • ↑ Inflammatory markers suggests inflammation
Coeliac serology
  • Exclude coeliac disease
Stool tests Stool microscopy and culture (including C. difficle toxin)
  • Exclude infective gastroenteritis or pseudomembranous colitis (C. difficle infection)
Note that presence of infection does not exclude Crohn's
Faecal calprotectin
  • ↑ Faecal calprotectin suggests inflammation
 
Some other tests:
  • TFT - hyperthyroidism can cause diarrhoea
  • Serology (note that it has limited role in diagnosing inflammatory bowel diseases but is common in exam)
    • ↑ pANCA
    • ↑ ASCAAnti-Saccharomyces cerevisiae antibodies

Ileocolonoscopy with biopsy of involved and uninvolved mucosa is the gold standard diagnostic test.
 
Category Crohn’s Disease Ulcerative Colitis
Macroscopic Findings Distribution / location:
  • Skip lesions - discontinuous pattern of involvement
  • Ileum involvement almost always present
  • Rectal sparing is common

Appearance:
  • Shallow ulcers (aphthous ulcers)
  • Cobblestone appearance (inflamed sections interspread with deep ulcerations that resemble cobblestones)
  • Strictures
 Distribution / location:
  • Continuous inflammation
  • Rectal involvement almost always present
  • Rarely extend proximal to the ileum

Appearance:
  • Friable mucosa with bleeding on contact
  • Pseudopolyps (raised areas of normal mucosa from repeat ulceration and healing)
Histology Findings
  • Transmural inflammation (full-thickness involvement)
  • Non-caseating granulomas (specific but not always present)
  • Increase in goblet cells
  • Mucosal / submucosal inflammation
  • Crypt abscesses
  • Absence of granulomas
  • Reduce in goblet cells

Imaging is essential for diagnosis in Crohn's disease, as Crohn's tend to affect any part of the GI tract, especially the small bowel which is not visualised by ileocolonoscopy.
 
Imaging modality Findings
Cross-sectional enterography (CT / MR)
  • Mesenteric fat stranding (suggest transmural inflammation)
  • Excessive mesenteric fat around affected bowel segment (Creeping fat sign)
  • Intestinal wall oedematous thickening

Can also identify
  • Strictures
  • Fistula
  • Abscesses
CT AP with IV contrast Usually only used in acutely unwell patients who canot tolerate oral contrast
Small bowel follow-through (with barium contrast)
  • Fistula
  • Bowel narrowing (string sign)
 

1st line: conventional corticosteroid monotherapy
  • Oral prednisolone / IV methylprednisolone / IV hydrocortisone
  • Conventional steroids are the most effective in inducing remission

2nd line: budesonide monotherapy
  • Less effective but fewer side effects

3rd line: aminosalicylate monotherapy (e.g. mesalazine, sulfasalazine)

 

In children / young people, exclusive enteral nutrition is the preferred method to induce remission, to avoid use of corticosteroids (esp. when growth or steroid side effects are a concern)

  • Exclusive enteral nutrition involves a nutritionally complete liquid diet, excluding regular foods, typically given for 6–8 weeks
  • It induces remission by supporting nutritional needs, modifying the microbiome and immune response, protecting the gut barrier, and eliminating harmful dietary triggers

Add-on therapy is indicated if:
  • Steroid dose cannot be tapered, or
  • ≥2 exacerbations in 1 year (despite on steroids)

Add-on drugs (to be added onto the corticosteroid but NOT monotherapy):
  • 1st line:  azathioprine / mercaptopurine
  • 2nd line: methotrexate

 

Assess TPMT activity before starting azathioprine / mercaptopurine.

  • Do not offer the drug if there is TPMT activity deficiency
  • Offer lower dose if TPMT activity is below normal but not deficient

TPMT is the enzyme that metabolises the drug and its metabolites, converting them into inactive form. If azathioprine / mercaptopurine is given to those with TPMT deficiency, the drug could accumulate and cause myelosuppression.

Consider TNF-α inhibitor if there is no response to conventional therapy:
  • Infliximab / adalimumab monotherapy or combine with an immunosupressant

Consider:
  • Ustekinumab (IL12, 23 inhibitor), or 
  • Vedolizumab (anti-α4β7)

For all patients:
  • Smoking cessation
  • Colonoscopic surveillance for colorectal cancer prevention
 
Offer patient to choose between receiving and not receiving maintenance treatment.
 

If maintenance treatment is decided:
  • 1st line:  azathioprine / mercaptopurine
  • 2nd line: methotrexate

Do not offer steroids to maintain remission.

 

Assess TPMT activity before starting azathioprine / mercaptopurine.

  • Do not offer the drug if there is TPMT activity deficiency
  • Offer lower dose if TPMT activity is below normal but not deficient


TPMT is the enzyme that metabolises the drug and its metabolites, converting them into inactive form. If azathioprine / mercaptopurine is given to those with TPMT deficiency, the drug could accumulate and cause myelosuppression.

References

Author: Adams Lau
Reviewer:
Last edited: 04/08/25