Previous changes

June 2023 — minor update. A recommendation to ask about sexual history, particularly in men who have sex with men, has been added to this topic in line with the British Association of Sexual Health and HIV (BASHH) United Kingdom national guideline for the management of sexually transmitted enteric infections 2023.

May 2021 — minor update. Information that unexplained chronic diarrhoea is an HIV indicator condition has been added to this topic in line with the British HIV Association/British Association for Sexual Health and HIV/British Infection Association Adult HIV testing guidelines 2020.

December 2018 — reviewed. A literature search was conducted in September 2018 to identify evidence-based guidelines, UK policy, systematic reviews, and key RCTs published since the last revision of the topic. New recommendations have been added to the referral section, reflecting the National Institute for Health and Care Excellence guideline on Suspected cancer: recognition and referral [NICE, 2015a]. In the scenario on chronic diarrhoea, there have been changes to the assessment section and new tests to consider have been added to the recommendations on investigations.

March 2013 — reviewed. A literature search was conducted in February 2013 to identify evidence-based guidelines, UK policy, systematic reviews, and key RCTs published since the last revision of the topic. There are no changes to the recommendations.

September to December 2010 — this is a new CKS topic. The evidence-base has been reviewed in detail, and recommendations are clearly justified and transparently linked to the supporting evidence.

New evidence

Evidence-based guidelines

No new evidence-based guidelines since 1 November 2023.

HTAs (Health Technology Assessments)

No new HTAs since 1 November 2023.

Economic appraisals

No new economic appraisals relevant to England since 1 November 2023.

Systematic reviews and meta-analyses

No new systematic review or meta-analysis since 1 November 2023.

Primary evidence

No new primary evidence which reaches the CKS threshold for inclusion published since 1 November 2023.

New policies

No new national policies or guidelines since 1 November 2023.

New safety alerts

No new safety alerts since 1 November 2023.

Changes in product availability

No changes in product availability since 1 November 2023.

What causes acute diarrhoea?

• Worldwide, acute diarrhoea is most commonly caused by infection [BMJ Best Practice, 2023a]. 
  • Viruses are the most common infectious cause in the community.
    • Among people who consult their GP, norovirus is one of the most common organisms isolated, as well as sapovirus and rotavirus [Tam, 2012a]. Norovirus is the most common cause of sporadic outbreaks of gastroenteritis affecting all age groups [GBD, 2018].
  • Bacterial causes include infection with Salmonella species, Campylobacter jejuni, Shigella species, and Escherichia coli [UKHSA, 2023]. 
    • Campylobacter jejuni is one of the most common organisms isolated among people who consult their GP [Tam, 2012b]. 
    • Clostridioides difficile can cause infectious diarrhoea in people who have taken antibiotics, especially those who are older, immunocompromised, or have been in hospital [GBD, 2018]. For more information, see the CKS topic on Diarrhoea - antibiotic associated.
  • Parasitic causes are the most common infections causing persistent diarrhoea. Protozoa are important and include Cryptosporidium, Giardia, Entamoeba histolytica, and Cyclospora. Protozoan and bacterial infections may cause persistent diarrhoea (duration of 14 days or more). 
  • Infections that can present with bloody diarrhoea include [BMJ Best Practice, 2023a]: 
    • Bacterial: Campylobacter jejuni, Salmonella, Escherichia coli O157:H7, Vibrio parahaemolyticus, Shigella, Yersinia, Aeromonas, Clostridioides difficile.
    • Viruses: cytomegalovirus.
    • Parasites: Entamoeba histolytica, schistosomiasis.
  • For more information on infectious causes, see the CKS topic on Gastroenteritis.
• Drugs associated with diarrhoea include laxatives, allopurinol, angiotensin-II receptor blockers, antibiotics, chemotherapy, magnesium-containing antacids, metformin, nonsteroidal anti-inflammatory drugs, proton pump inhibitors, and selective serotonin reuptake inhibitors [Arasaradnam, 2018].  
  • For more information on specific drugs and whether diarrhoea is a reported adverse effect, see the manufacturer's Summary of Product Characteristics at www.medicines.org.uk/emc.
• Other causes of acute diarrhoea include [BMJ Best Practice, 2023a]: 
  • Anxiety.
  • Food allergy. 
  • Acute appendicitis.
  • Pelvic radiation treatment.
  • Intestinal ischaemia.
  • Early presentation of a chronic cause (for example, a first presentation of inflammatory bowel disease).

What causes chronic diarrhoea?

• Chronic diarrhoea has a broader differential diagnosis than acute diarrhoea. More common causes of chronic diarrhoea include [Arasaradnam, 2018]: 
  • Irritable bowel syndrome 
    • Irritable bowel syndrome is a functional disorder of the bowel. It is characterized by frequent episodes of bowel disturbance, abdominal discomfort or pain, and bloating, which may affect daily activities. Diet or stress may exacerbate symptoms. The cause is unclear, but there may be an association with increased bowel sensitivity or abnormal muscle activity in the bowel wall [NICE, 2017]. Associated symptoms include headache, back pain, and psychosocial distress. 
    • For more information, see the CKS topic on Irritable bowel syndrome.
  • Diet 
    • For example, fermentable oligo-, di-, mono-saccharides and polyols (FODMAP) malabsorption, artificial sweeteners such as sorbitol, caffeine, and excess alcohol [Arasaradnam, 2018]. 
  • Inflammatory bowel disease (Crohn's disease, ulcerative colitis).
    • For more information, see the CKS topics on Crohn's disease and Ulcerative colitis.
  • Microscopic colitis 
    • Microscopic colitis is a clinicopathological diagnosis that causes chronic watery diarrhoea, especially in older women. Other symptoms may be non-specific but include abdominal pain, weight loss and arthralgia [Gentile, 2018].
  • Coeliac disease
    • Coeliac disease is a common autoimmune disorder in which there is a heightened immunological response to gluten. Coeliac disease can present in adulthood (fourth or fifth decade) with symptoms including abdominal pain, change in bowel habits, and anaemia, although people with the condition do not always have abdominal symptoms or signs of malabsorption. For more information, see the CKS topic on Coeliac disease.
  • Other causes of malabsorption
    • These include lactose intolerance and pancreatic insufficiency.  
  • Colorectal cancer
    • Colorectal cancer may present as diarrhoea. There may be rectal bleeding or blood mixed in with the stools and a palpable rectal or abdominal mass. Weight loss and iron deficiency anaemia may also feature. For more information, see the CKS topic on Gastrointestinal tract (lower) cancers - recognition and referral.
  • Bile acid diarrhoea
    • Bile acid diarrhoea is due to imbalances in bile acid homeostasis in the enterohepatic circulation and may occur as a result of ileal disease or dysfunction (such as Crohn's disease or terminal ileum resection) or be idiopathic. Excess bile acid in the colon causes diarrhoea through effects on electrolyte balance and speeding up of large bowel transit time [Hughes, 2021]. 
  • Drugs
    • Examples include antibiotics (particularly macrolides such as erythromycin), antihypertensives (for example, ACE inhibitors), nonsteroidal anti-inflammatory drugs, hypoglycaemic drugs (such as metformin and gliptins), magnesium-containing products, proton pump inhibitors, selective serotonin reuptake inhibitors, antineoplastic drugs, theophyllines, antiarrhythmics, and furosemide  [Arasaradnam, 2018].  
    • For more information on specific drugs and whether diarrhoea is a reported adverse effect, see the manufacturer's Summary of Product Characteristics at www.medicines.org.uk/emc.
  • Constipation and faecal impaction (leading to overflow) [Arasaradnam, 2018].  
    • This is common in frail older people.  
• Other less common diagnoses to consider include [Arasaradnam, 2018]:
  • Infection — it is unusual for chronic diarrhoea to be caused by an infection in an immunocompetent person, although chronic infections can result from protozoan infections (for example, giardiasis and amoebiasis). 
  • HIV infection — unexplained chronic diarrhoea is an HIV indicator condition [John, 2021]. For more information, see the CKS topic on HIV infection and AIDS.  
  • Small bowel bacterial overgrowth.
  • Mesenteric ischaemia.
  • Lymphoma.
  • Surgical causes (for example, small bowel resection, internal fistulae).
  • Chronic pancreatitis, pancreatic carcinoma.
  • Radiation enteropathy.
  • Endocrine disorders — for example, hyperthyroidism, diabetes (may be metformin-associated), hypoparathyroidism, Addison’s disease.
  • Cystic fibrosis.
  • Factitious diarrhoea — the person adds water to their stools or uses laxatives. 
  • Small bowel enteropathy (for example, Whipple’s disease, tropical sprue, amyloid).
  • Hormone-secreting tumours (for example, VIPoma, gastrinoma, carcinoid).
  • Autonomic neuropathy.
  • Brainerd diarrhoea (possibly due to an infectious cause, but not identified).

How should I assess a person with acute diarrhoea?

• Determine the onset, duration, frequency, and severity of symptoms.
  • The onset of symptoms within 6 hours of contaminated food suggests a pre-formed toxin of either Bacillus cereus or Staphylococcus aureus as the cause.
  • More frequent stool passage suggests an infectious cause.
  • Watery stools are associated with non-invasive and toxin-producing pathogens.
• Enquire about the presence of red flag symptoms:
  • Blood in the stool, which is usually seen with invasive pathogens or severe inflammation, e.g. ulcerative colitis.
  • Recent hospital treatment or antibiotic treatment. For more information, see the CKS topic on Diarrhoea - antibiotic associated.
  • Weight loss.
  • Evidence of dehydration.
  • Nocturnal symptoms — organic cause more likely.
• Also ask about sexual history (particularly in men who have sex with men) to exclude sexually transmitted enteric infection. 
• Attempt to ascertain the underlying cause. Assess for:
  • Quantity and character of stools (watery, fatty, containing blood or mucus).
  • Features suggesting infection, such as:
    • Fever — often seen with invasive pathogens e.g. Salmonella, Shigella, and Campylobacter, enteric viruses or a cytotoxic organism such as Clostridioides difficile.
    • Vomiting.
    • Recent contact with a person with diarrhoea.
    • Exposure to possible sources of enteric infection (for example certain foodstuffs such as meat, shellfish, dairy, and eggs), having eaten meals out, or recent farm or petting zoo visits).
    • Travel abroad — increases the likelihood of infection. Ask about potential exposures such as raw milk or untreated water.
    • Being in a higher risk group such as food handlers, nursing home residents (greater risk of norovirus, Cryptosporidium, and Giardia), and recently hospitalized people.
  • Any new drugs, especially antibiotics or laxatives. For examples, see the Causes section on Acute diarrhoea.
  • Stress or anxiety.
  • Abdominal pain, which is often present in inflammatory bowel disease, irritable bowel syndrome, and ischaemic colitis.
  • History of recent radiation treatment to the pelvis.
  • Factors increasing the risk of immunosuppression (for example, human immunodeficiency virus infection, long-term steroid use, or chemotherapy).
  • Any surgery or medical conditions (for example, endocrine disease) accounting for the diarrhoea. 
  • Diet and use of alcohol or substances such as sorbitol.
• Assess for complications of diarrhoea, such as dehydration.
  • Features indicating dehydration include increased pulse rate, reduced skin turgor, dryness of mucous membranes, delayed capillary refill time, decreased urine output, hypotension (check for postural changes), and altered mental status. For more detail, see Clinical features of dehydration.
  • Also consider underlying conditions that may increase the risk of complications.
• Perform an abdominal examination to assess for pain or tenderness, distension, mass, increased or decreased bowel sounds, or liver enlargement.
• Consider a rectal examination to assess for rectal tenderness, stool consistency, blood, mucus, and possible malignancy.
• If acute causes have been excluded and the person has features suggestive of an early presentation of a chronic cause, see Scenario: Chronic diarrhoea (more than 4 weeks).

How should I investigate acute diarrhoea in primary care?

• Send a faecal specimen for routine microbiology investigation if a person with diarrhoea has:
  • Symptoms/signs or a clinical indication:
    • The person is systemically unwell; needs hospital admission and/or antibiotics.
    • There is blood or pus in the stool.
    • The person is immunocompromised.
    • The person has recently received antibiotics, a proton pump inhibitor (PPI) or been in hospital — also request specific testing for Clostridioides difficile. For more information, see the CKS topic on Diarrhoea - antibiotic associated. 
    • Diarrhoea occurs after foreign travel — also request tests for ova, cysts, and parasites and state the countries visited on the form.
    • Amoebae, Giardia, or cryptosporidium are suspected, particularly if diarrhoea is persistent (2 weeks or more) or the person has travelled to an at-risk area.
    • There is a need to exclude infectious diarrhoea (for example, severe abdominal pain, exacerbation of inflammatory bowel disease, or irritable bowel syndrome).
  • A public health indication:
    • Diarrhoea in high-risk people (for example food handlers, healthcare workers, elderly residents in care homes).
    • Suspected food poisoning (for example after a barbeque or restaurant meal or eating eggs, chicken, or shellfish).
    • Outbreaks of diarrhoea in the family or community, when isolating the organism, may help pinpoint the source of the outbreak.
    • Contacts of people infected with certain organisms, for example, Escherichia coli O157 or C. difficile, where there may be serious clinical sequelae to an infection.
    • Close household contacts of a person with a Giardia infection.
• For more information on how to send a stool sample (such as what information to include), see Sending a stool sample.
• Consider blood tests if infection and the other causes of acute diarrhoea have been excluded and it is suspected that an episode of acute diarrhoea is due to a chronic cause.
  • See the section on Investigations in the Scenario: Chronic diarrhoea (more than 4 weeks) for advice on which blood tests to request.

When should I admit or refer a person with acute diarrhoea?

• Arrange emergency admission to hospital if:
  • The person is vomiting and unable to retain oral fluids, or
  • They have features of severe dehydration or shock (for more information, see Clinical features of dehydration).
• Other factors that influence the threshold for admission include (use clinical judgment):
  • Older age (people 60 years of age or older are more at risk of complications).
  • Home circumstances and level of support.
  • Fever.
  • Bloody diarrhoea.
  • Abdominal pain and tenderness.
  • Increased risk of poor outcome, for example:
    • Coexisting medical conditions — immunodeficiency, lack of stomach acid, inflammatory bowel disease, valvular heart disease, diabetes mellitus, renal impairment, rheumatoid disease, systemic lupus erythematosus.
    • Drugs — immunosuppressants or systemic steroids, proton pump inhibitors, angiotensin-converting enzyme inhibitors, diuretics.
• Refer adults using a suspected cancer pathway referral (adult to receive a diagnosis or ruling out of cancer within 4 weeks of urgent referral from GP) for colorectal cancer if:
  • They have a positive quantitative faecal immunochemical test (FIT), which has been requested because:
    • They are aged 40 and over with unexplained weight loss and abdominal pain, or
    • They are aged 50 and over with unexplained rectal bleeding, or
    • They are aged 60 and over with iron deficiency anaemia or changes in their bowel habit, or tests show occult blood in their faeces.
• Consider a suspected cancer pathway referral (adult to receive a diagnosis, or ruling out of cancer within 4 weeks of urgent referral from GP) where: 
  • Adults have a positive quantitative faecal immunochemical test (FIT), which has been requested because:
    
    • Adults have 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 habits.
      • Weight loss.
      • Iron-deficiency anaemia.
• Refer if the diagnosis remains uncertain after a primary care assessment — if infection and the other common causes of acute diarrhoea have been excluded and it is suspected that an episode of acute diarrhoea is due to a chronic cause. 

How should I assess a person with chronic diarrhoea?

• Determine the duration, frequency, pattern, and severity of symptoms.
• Ask about and look for red flag indicators (symptoms and/or features that may be caused by another condition that needs referral or further investigation). These include: 
  • Unexplained weight loss.
  • Unexplained rectal bleeding.
  • Persistent blood in the stool.
  • Abdominal mass.
  • Rectal mass.
  • Severe abdominal pain.
  • Iron deficiency anaemia.
  • Raised inflammatory markers (may indicate inflammatory bowel disease).
  • Nocturnal or continuous diarrhoea or both (suggestive of an organic rather than functional disorder).
  • Fever, tachycardia, hypotension, dehydration.
• Look for other features suggestive of an underlying cause, including:
  • Travel abroad — consider an infective cause, especially Giardia.
  • Laxative use (including for treatment of hepatic encephalopathy).
  • Other drugs. For examples, see the section on chronic causes of diarrhoea.
    • Recent use of an antibiotic or proton pump inhibitor is associated with Clostridioides difficile infection.
  • Chronic fatty diarrhoea — suggests fat maldigestion (for example pancreatic insufficiency) or fat malabsorption (for example coeliac disease).
  • Previous abdominal surgery — suspect bile acid diarrhoea if the person has a history of cholecystectomy or ileal resection.
  • Family history of coeliac disease or inflammatory bowel disease.
  • Diet and relationship of symptoms to eating — lactose intolerance is suggested if symptoms are worsened by dairy products; diarrhoea may be due to consumption of caffeine or food additives, such as sorbitol.
  • Excessive alcohol intake — can cause a toxic effect on intestinal epithelium or rapid gut transit.
  • Abdominal pain — may indicate coeliac disease, Crohn's disease, or malignancy.
  • Weight loss, anxiety, palpitations, tremors — consider hyperthyroidism.
  • Lifelong history of constipation — consider impaction with overflow diarrhoea.
  • Immunocompromised person — consider opportunistic infection with parasites (for example Giardia, Cryptosporidium, and Cyclospora).
  • Features of systemic disease (such as thyrotoxicosis, diabetes, adrenal insufficiency).
  • Systemic illness affecting gastrointestinal motility (for example scleroderma, diabetes mellitus); history of inflammatory bowel disease; previous gastrointestinal surgery with risk of stricture — consider small intestinal bacterial overgrowth (SIBO).
  • Rashes (for example pyoderma gangrenosum or erythema nodosum in inflammatory bowel disease; hyperpigmentation in Addison's disease; and dermatitis herpetiformis in coeliac disease).
• Assess for features that indicate a diagnosis of irritable bowel syndrome.
  • For more information, see the CKS topic on Irritable bowel syndrome.
• Perform an abdominal examination, looking for distension, an abdominal mass, organomegaly, or tenderness.
• Perform a digital rectal examination, provided this is acceptable to the person being examined. Note any faecal leakage, haemorrhoids, type of stool, and presence of blood.

How should I investigate chronic diarrhoea in primary care?

Tailor investigations to the individual, and if necessary, refer for further investigation.

• Request the following blood tests in all people with chronic diarrhoea:
  • Full blood count — to detect anaemia.
  • Urea and electrolytes.
  • Liver function tests, including albumin level.
  • Calcium.
  • Vitamin B₁₂ and red blood cell folate.
  • Iron status (ferritin).
  • Thyroid function tests.
  • ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein). 
  • Testing for coeliac disease — immunoglobulin A (IgA), and IgA tissue transglutaminase (tTG), or IgA endomysial antibody (EMA).
    • Note that antibodies usually will become negative when a person is on a gluten-free diet, so the test should be carried out when they are eating a diet containing gluten.
    • For more information, see the CKS topic on Coeliac disease. 
• Consider CA125 testing if there are symptoms suggestive of ovarian cancer. For more information, see the CKS topic on Ovarian cancer.
• Consider HIV serology if underlying immunodeficiency is suspected. For more information, see the CKS topic on HIV infection and AIDS. 
• Consider sending stool for:
  • Routine microbiology investigation and examination for ova, cysts and parasites, if an infectious cause is suspected or there is a history of exotic foreign travel.
    • Send three specimens at least 2 days apart, as ova, cysts, and parasites are shed intermittently.
    • For more information on how to send a stool sample, see Sending a stool sample in the Scenario: Acute diarrhoea (less than 4 weeks).
  • Clostridium difficile testing, particularly if the person has recently been admitted to hospital or treated with antibiotics or a proton pump inhibitor, or if a previous episode has resolved and the symptoms have recurred. For more information, see the CKS topic on Diarrhoea - antibiotic associated.
  • Faecal calprotectin testing to help differentiate between irritable bowel syndrome and inflammatory bowel disease in people under the age of 40 years if specialist assessment is being considered and cancer is not suspected. 
    • Note that faecal calprotectin should not be used for people:
      • With new onset rectal bleeding or bloody diarrhoea.
      • In whom there is a need to rule out cancer. 
    • For more information, see the CKS topics on Crohn's disease and Ulcerative colitis. 
  • Testing for blood in the faeces in people with symptoms suggestive of colorectal cancer who do not meet suspected cancer referral pathway criteria.

When should I refer a person with chronic diarrhoea?

• Refer adults using a suspected cancer pathway referral (adult to receive a diagnosis or ruling out of cancer within 4 weeks of urgent referral from GP) for colorectal cancer if:
  • They are aged 40 and over with unexplained weight loss and abdominal pain, or
  • They are aged 50 and over with unexplained rectal bleeding, or
  • They are aged 60 and over with iron deficiency anaemia or changes in their bowel habit, or tests show occult blood in their faeces.
• Consider a suspected cancer pathway referral (adult to receive a diagnosis, or ruling out of cancer within 4 weeks of urgent referral from GP) for colorectal cancer in: 
  • Adults 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 habits.
    • Weight loss.
    • Iron-deficiency anaemia.
• Refer for further assessment and management if:
  • History, examination, and blood test results suggest any of the following:
    • Coeliac disease. For more information, see the CKS topic on Coeliac disease.
    • Crohn's disease. For more information, see the CKS topic on Crohn's disease. 
    • Ulcerative colitis. For more information, see the CKS topic on Ulcerative colitis. 
    • Bile acid diarrhoea. 
    • Microscopic colitis.
    • Malabsorption.
  • A person less than 40 years of age does not have typical symptoms of functional bowel disorder and/or has severe symptoms and documented diarrhoea. 
  • The diagnosis is uncertain.