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Red flag refreshers – diarrhoea

Diarrhoea is a common symptom and one of the most frequent reasons for consulting a GP. Diarrhoea is defined as the passage of three or more loose stools per day and can be classified as acute (lasting less than 14 days), persistent (lasting more than 14 days) and chronic (lasting longer than four weeks).1 Although the majority of episodes of diarrhoea are short-lived, self-limiting and benign, many are not and identifying those cases that represent potentially life-limiting illness can be a challenge.

What are the potential serious causes of diarrhoea?

The potentially serious causes of diarrhoea include:

  • Bowel cancer.
  • Inflammatory bowel disease.
  • Clostridium difficile diarrhoea.
  • Ischaemic colitis.
  • Pancreatic cancer.

All of these can lead to death or significant morbidity.

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However, the most common cause of acute diarrhoea is infective. In the community this is most commonly due to a virus but can also have bacterial or parasitic causes. Up to 25% of people in the UK report an episode of infectious diarrhoea per year.2 Other frequent causes of diarrhoea include drugs (laxatives, allopurinol, angiotensin-II receptor blockers, antibiotics, chemotherapy, magnesium-containing antacids, metformin, NSAIDs, PPIs and SSRIs), stress, food allergy, recent pelvic irradiation, and can be the first presentation of a chronic cause.

Chronic diarrhoea has a broader differential diagnosis including:

  • Irritable bowel syndrome.
  • Dietary.
  • Coeliac disease.
  • Bile acid diarrhoea.
  • Lactose intolerance.
  • Microscopic colitis.
  • Inflammatory bowel disease.
  • Cancer (bowel and pancreatic).
  • Pancreatic exocrine insufficiency.

One further consideration is overflow diarrhoea due to constipation and faecal impaction; this can be seen in both younger patients and frail elderly patients.

Red flags

The initial assessment should include onset, duration, frequency and severity of symptoms. At this point it is vital to identify reg flags.1

Signs and symptoms

Red flag symptoms and signs for significant disease include:

  • In acute diarrhoea:
    • Evidence of dehydration or shock (tachycardia, systolic blood pressure <90mmHg, weakness, confusion, oliguria or anuria, marked peripheral vasoconstriction)
    • Unintentional weight loss
    • Rectal bleeding
  • In chronic diarrhoea:
    • Unexplained weight loss
    • Unexplained rectal bleeding
    • Anaemia
    • Abdominal or rectal mass
    • Family history of bowel or ovarian cancer

Other important features in the history are recent antibiotic use or hospital admission, a family history of coeliac disease or inflammatory bowel disease, previous abdominal surgery (previous cholecystectomy or ileal resection raises the suspicion of bile acid diarrhoea), presence of steatorrhea, chronic history of constipation (causing possible overflow diarrhoea), foreign travel, drugs (illicit, over the counter and prescribed) and potential dietary causes. Symptoms suggestive of an organic disorder include nocturnal diarrhoea, continuous diarrhoea, onset after 45 years of age and significant weight loss.


Many people with a single self-limiting episode of diarrhoea will not require any investigation. However, a stool specimen for culture and C. difficile toxin should be requested for patients with certain features – if the patient is systemically unwell or requiring hospital admission, if they have rectal bleeding, recent antibiotic use, recent foreign travel, suspected food poisoning and in those who are immunocompromised.

Testing in primary care for those with persistent symptoms and the absence of red flags, should include, a stool culture, full blood count, C-reactive protein, thyroid function and coeliac serology. For patients in whom the likely diagnosis is irritable bowel syndrome, but inflammatory bowel disease is a concern, a faecal calprotectin should be performed. Consider HIV testing if immunodeficiency is suspected.3,4,5

What action needs to be taken?

This partly depends on the acuity of the presentation and the severity of the illness. Viral diarrhoea usually lasts around 2-3 days, whereas untreated bacterial diarrhoea can last between 3-7 days.

Hospital admission should be considered if a patient with diarrhoea is showing signs of severe dehydration or is unable to retain oral fluids. If the presentation is that of acute diarrhoea, with abdominal pain and recurrent rectal bleeding, hospital admission should be considered; this may be the first presentation of inflammatory bowel disease or could be due to ischaemic colitis both of which require urgent evaluation and treatment. Other factors that may influence admission include increasing age, systemically unwell, level of social support, fever and medical comorbidity.

Patients should be referred to secondary care if suffering with chronic diarrhoea with the presence of red flags. Chronic diarrhoea may be a symptom of bowel cancer. As per the NICE guidelines on suspected cancer adults under the age of 50 with a change in bowel habit should be considered for a referral on the two-week wait pathway for assessment.6

Patients with suspected coeliac disease or inflammatory bowel disease on initial testing should be referred to secondary care for assessment. In patients where bile acid diarrhoea is suspected consider referral for formal diagnosis with SeHCAT testing.

For those patients with persisting symptoms in which initial evaluation has not revealed a cause consider making a positive diagnosis of irritable bowel syndrome or functional diarrhoea. However, consider secondary care referral for those patients with severe, persistent or atypical symptoms. Chronic diarrhoea can impair patients’ quality of life and this can manifest as avoidance of work, travel or socialising and food avoidance to avoid exacerbating foods.7

Most people with acute diarrhoea, a negative stool culture, normal blood tests, and no red flag features can usually be managed in primary care. In patients with chronic diarrhoea, consider referral for those with red flags or in cases of diagnostic uncertainty.

Dr Benjamin Disney is a Gastroenterology consultant at University Hospitals Coventry & Warwickshire NHS Trust.


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