Which initial investigations should be conducted for a patient suspected of having Inflammatory Bowel Disease?

Initial investigations for a patient suspected of having inflammatory bowel disease (IBD) should include:

• Blood tests: full blood count to detect anaemia, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to assess inflammation, liver function tests including albumin, calcium, vitamin B12, red blood cell folate, iron studies (ferritin), and thyroid function tests NICE CKS.
• Serological testing for coeliac disease using immunoglobulin A (IgA) and IgA tissue transglutaminase (tTG) or endomysial antibody (EMA) to exclude coeliac disease as a cause of symptoms NICE CKS.
• Faecal calprotectin testing to help differentiate IBD from irritable bowel syndrome in people under 40 years if cancer is not suspected; however, it should not be used if there is new onset rectal bleeding or bloody diarrhoea or if cancer needs to be ruled out NICE CKS.
• Stool samples for routine microbiology and examination for ova, cysts, and parasites if infection or travel history suggests an infectious cause NICE CKS.
• Colonoscopy with multiple intestinal biopsies for histological confirmation and classification of disease extent and severity, which is essential for diagnosis of both Crohn's disease and ulcerative colitis NICE CKS,NICE CKS.
• Upper gastrointestinal endoscopy in children and young people, and in adults with upper GI symptoms, to differentiate Crohn's disease from ulcerative colitis NICE CKS,NICE CKS.
• Imaging studies such as magnetic resonance enterography (MRE) or MRI of the small bowel, small bowel ultrasound, or capsule endoscopy may be needed if endoscopy and conventional imaging are inconclusive NICE CKS,NICE CKS.
• Additional imaging like pelvic MRI for suspected perianal disease, abdominal ultrasound, CT scans, and plain abdominal X-rays may be used to assess complications and disease extent NICE CKS,NICE CKS.