Investigations of diarrhoea

Basic investigations carried out in chronic diarrhoea include: (1)

• blood work
  • complete blood count
  • ESR and CRP
  • liver function testing
  • for malabsorption vitamin B12, folate, calcium, ferritin
  • thyroid-stimulating hormone level
  • electrolyte levels
• serological tests for coeliac disease
  • tissue transglutaminase antibody (tTGA), or IgA endomysium antibody (EMA)
• stool tests
  • stool for microscopy and culture for Giardia lamblia, Salmonella, Shigella and Campylobacter and for virology
  • ova and parasite examination
  • faecal calprotectin*
  • faecal leukocyte level and faecal immunochemical test**
  • Clostridium difficile stool toxin if indicated
  • stool laxative screen – if laxative abuse is suspected

Further investigations are carried our according to the history and investigations findings and may include:

• sigmoidoscopy or colonoscopy
• upper gastrointestinal endoscopy
• small bowel imaging e.g. - barium follow through

* NICE have stated (2):

• faecal calprotectin testing is recommended as an option to support clinicians with the differential diagnosis of inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS) in adults with recent onset lower gastrointestinal symptoms for whom specialist assessment is being considered, if:
  • cancer is not suspected, having considered the risk factors (for example, age)
• faecal calprotectin testing is recommended as an option to support clinicians with the differential diagnosis of IBD or non-IBD (including IBS) in children with suspected IBD who have been referred for specialist assessment, if:
  • appropriate quality assurance processes and locally agreed care pathways are in place for the testing

** NICE criteria for requesting test for occult blood in faeces (FIT) (3):

• should be offered to adults without rectal bleeding who:
  • are aged 50 or over with unexplained:
    • abdominal pain or weight loss
  • or are aged under 60 with:
    • changes in their bowel habit or
    • iron-deficiency anaemia
  • or are aged 60 or over and have anaemia without iron deficiency

Notes:

• NICE urgent colorectal cancer guidance (4):
  • Refer people using a suspected cancer pathway referral (for an appointment within 2 weeks) for colorectal cancer if:
    • they are aged 40 or over
      • with unexplained weight loss and abdominal pain
    • or they are aged 50 or over
      • with unexplained rectal bleeding
    • or they are aged 60 or over with:
      • iron-deficiency anaemia or
      • changes in their bowel habit, or
    • tests show occult blood in their faeces (for who should be offered a test for occult blood in faeces see below)
      
      
  • a suspected cancer referral (for an appointment within 2 weeks) should also be considered for:
    • people with a rectal or abdominal mass
    • adults aged under 50 with rectal bleeding and any of the following unexplained symptoms or findings:
      • abdominal pain
      • change in bowel habit
      • weight loss
      • iron-deficiency anaemia.

References:

1. Arasaradnam RP, Brown S, Forbes A, et al. Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition. Gut. 2018 Aug;67(8):1380-99.
2. NICE. Faecal calprotectin diagnostic tests for inflammatory diseases of the bowel. Diagnostics guidance DG11 published October 2013.
3. NICE. Quantitative faecal immunochemical testing to guide colorectal cancer pathway referral in primary care. Diagnostics guidance DG56 published August 2023
4. NICE. Suspected cancer: recognition and referral. NICE guideline NG12 published June 2015, last updated October 2023