Change in stool colour

Medicine > Gastrointestinal

Differential Diagnosis Schema 🧠

Red or Maroon Stool

Lower gastrointestinal bleeding: typically from haemorrhoids, diverticular disease, or colorectal cancer.
Upper gastrointestinal bleeding with rapid transit: large volume bleeding from peptic ulcers or oesophageal varices.
Infectious colitis: associated with diarrhoea, abdominal pain, and fever, often due to pathogens such as E. coli or Shigella.
Inflammatory bowel disease (IBD): typically presents with bloody diarrhoea and abdominal pain.
Angiodysplasia: more common in elderly patients, can cause intermittent painless bleeding.

Black or Tarry Stool

Upper gastrointestinal bleeding: often due to peptic ulcers, oesophagitis, or oesophageal varices, associated with melena.
Iron supplements: can cause dark green or black stools without other symptoms.
Bismuth-containing medications (e.g., Pepto-Bismol): can cause black stools due to bismuth sulphide formation.
Dietary causes: ingestion of black foods like liquorice or blueberries.

Pale or Clay-Coloured Stool

Biliary obstruction: often due to gallstones, pancreatic cancer, or biliary atresia in children, leads to pale stools and dark urine.
Hepatitis: viral, autoimmune, or drug-induced can impair bile production, leading to pale stools.
Chronic pancreatitis: associated with steatorrhea and pale, greasy stools due to fat malabsorption.
Cystic fibrosis: in children, may present with pale, bulky stools due to pancreatic insufficiency.

Green Stool

Rapid transit through the intestines: often seen in diarrhoea where bile does not have time to be fully broken down.
Dietary factors: ingestion of green vegetables or foods with green colouring.
Infectious gastroenteritis: can cause green stool due to rapid transit and infection.
Antibiotics: certain antibiotics can alter gut flora and cause green stools.

Yellow Stool

Steatorrhea: typically due to fat malabsorption seen in conditions like chronic pancreatitis, coeliac disease, and cystic fibrosis.
Giardiasis: parasitic infection causing yellow, foul-smelling stools with diarrhoea.
Liver disease: can lead to impaired bile production, causing yellow stools.

Key Points in History 🥼

Symptom Onset and Duration

Acute onset: may suggest infection, ischaemia, or acute bleeding.
Chronic or intermittent: often points towards inflammatory or neoplastic causes.

Associated Symptoms

Abdominal pain: consider peptic ulcer disease, IBD, or biliary causes.
Weight loss: raises suspicion for malignancy, chronic infections, or malabsorption.
Diarrhoea: suggests infectious causes, IBD, or malabsorption syndromes.
Fever: often indicative of infectious or inflammatory processes.
Pruritus: may suggest cholestasis or hepatic causes.

Background

Past medical history: chronic liver disease, IBD, or known malignancies.
Drug history: NSAIDs (risk of ulcers), antibiotics (risk of C. difficile infection), iron supplements (black stools).
Family history: IBD, colorectal cancer.
Social history: alcohol use (liver disease), recent travel (risk of infectious diarrhoea).

Possible Investigations 🌡️

Laboratory Tests

Full blood count: may show anaemia in bleeding, leukocytosis in infection.
Liver function tests: deranged in biliary obstruction, hepatitis.
Coagulation profile: abnormal in liver disease or bleeding disorders.
Stool cultures: to identify infectious causes, including C. difficile.
Faecal occult blood test: to detect hidden blood in stools.

Imaging Studies

Abdominal ultrasound: first-line for biliary or hepatic causes.
CT abdomen: useful for identifying masses, perforations, or advanced disease.
Colonoscopy: indicated for investigation of lower GI bleeding, neoplasia, or IBD.
Upper endoscopy (OGD): indicated in suspected upper GI bleeding or malignancy.

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