Black stool (melena)

Black stool (melena): When is it serious - and when do you need a gastroscopy?

Black, tarry stool is medically called melena and is one of the classic alarm symptoms in the gastrointestinal tract. It is most often caused by bleeding from the upper gastrointestinal tract - oesophagus, stomach or duodenum - where blood is digested by gastric acid and bacteria and turns the stool black [1]. Up to 80% of cases are caused by a source that can be seen at gastroscopy.

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Why does the stool turn black?

To produce melena, blood must have been in the gastrointestinal tract for at least 6-8 hours, and there must be at least 50 ml of blood [1]. Haemoglobin is converted to haematin and iron sulphide, which colours the stool shiny black and gives it a characteristic sweetish, foul-smelling odour.

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The most common causes

Source	Frequency	Typical signs
Peptic ulcer	30-50%	Epigastric pain, Helicobacter pylori, NSAID use
Erosive gastritis	10-20%	Painkillers, alcohol, stress
Oesophageal varices	5-15%	Liver cirrhosis, concurrent haematemesis (vomiting blood)
Acid reflux (GERD) with oesophagitis	5-10%	Heartburn, painful swallowing
Mallory-Weiss tear	5%	After forceful vomiting
Gastric cancer	2-5%	Weight loss, loss of appetite, age >50

False melena (not bleeding) can be caused by: iron supplements, liquorice, blueberries, charcoal tablets, bismuth.

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When to seek help - urgently?

Call 112 or the out-of-hours number 1813 if you have:

• Black stool + dizziness, pallor, palpitations, collapse
• Black stool + bloody or "coffee-grounds" vomit
• Black stool + severe abdominal pain
• Known liver cirrhosis or bleeding disorder

With clear melena accompanied by dizziness and fatigue, you should be referred acutely or subacutely to hospital - this suggests significant blood loss requiring rapid stabilisation and possible blood transfusion.

NICE CG141, recommendation 1.3.1: "Offer endoscopy to unstable patients with severe acute upper gastrointestinal bleeding immediately after resuscitation." [5]

With suspected melena without other symptoms and a stable haemoglobin (low-risk patient with a Glasgow-Blatchford score ≤1), investigation and treatment can be carried out as an outpatient at a specialist clinic with gastroscopy within 24 hours.

ESGE 2021, recommendation 1: "ESGE recommends in patients with acute upper gastrointestinal hemorrhage (UGIH) the use of the Glasgow-Blatchford Score (GBS) for pre-endoscopy risk stratification. Patients with GBS ≤1 are at very low risk of rebleeding, mortality within 30 days, or needing hospital-based intervention and can be safely managed as outpatients with outpatient endoscopy." [6]

NICE CG141, recommendation 1.1.2: "Consider early discharge for patients with a pre-endoscopy Blatchford score of 0." [5]

Black stool alone - without other symptoms - requires contact with your GP or specialist within a few days.

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How melena is investigated

1. History: NSAIDs, anticoagulants, alcohol, iron supplements, previous peptic ulcer.
2. Clinical examination: pulse, blood pressure, need for transfusion.
3. Blood tests: haemoglobin, ferritin, INR, liver tests, urea (elevated in upper GI bleeding).
4. Oral gastroscopy - gold standard, performed within 24 hours of acute bleeding [2].
5. Nasal gastroscopy - a gentler alternative to oral gastroscopy, without sedation.
6. Colonoscopy - considered if gastroscopy fails to show a source (~5-10%).

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Treatment

Acute:

• Stabilisation with fluids and possibly blood transfusion
• IV proton pump inhibitor (PPI)
• Endoscopic haemostasis at gastroscopy: clips, adrenaline injection, thermocoagulation [3]
• For varices: band ligation

Subacute and preventive:

• Eradication of Helicobacter pylori for peptic ulcer - reduces recurrence from ~60% to <10% [4]
• Stop NSAIDs, or switch to PPI-protected treatment
• Reduce alcohol
• Oncological work-up for cancer-suspect findings

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Treatment at Kirurgen.dk

We offer outpatient oral and nasal gastroscopy under the public health insurance scheme - typically within 1-2 weeks. See also our articles on Helicobacter pylori and peptic ulcer, GERD reflux and nasal vs. oral gastroscopy.

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References

1. Wilkins T, Khan N, Nabh A, Schade RR. Diagnosis and management of upper gastrointestinal bleeding. Am Fam Physician 2012;85(5):469-76.
2. Barkun AN, Almadi M, Kuipers EJ, et al. Management of nonvariceal upper gastrointestinal bleeding: international consensus group. Ann Intern Med 2019;171(11):805-22.
3. Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI. ACG clinical guideline: upper gastrointestinal and ulcer bleeding. Am J Gastroenterol 2021;116(5):899-917.
4. Ford AC, Gurusamy KS, Delaney B, Forman D, Moayyedi P. Eradication therapy for peptic ulcer disease in Helicobacter pylori-positive people. Cochrane Database Syst Rev 2016;(4):CD003840.
5. National Institute for Health and Care Excellence (NICE). Acute upper gastrointestinal bleeding in over 16s: management. Clinical Guideline CG141, 2012 (updated 2016). nice.org.uk/guidance/cg141
6. Gralnek IM, Stanley AJ, Morris AJ, et al. Endoscopic diagnosis and management of nonvariceal upper gastrointestinal hemorrhage (NVUGIH): ESGE Guideline - Update 2021. Endoscopy 2021;53(3):300-332.
7. Blatchford O, Murray WR, Blatchford M. A risk score to predict need for treatment for upper-gastrointestinal haemorrhage. Lancet 2000;356(9238):1318-21.

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See also

Peptic ulcer