Melaena (Black Stools) | Nuffield Health

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What is melaena?

Melaena is the medical term for black, tarry stools (poo) with an unusually strong, unpleasant smell. It happens when blood from higher up in your digestive system travels through your gut and is broken down along the way.

What causes melaena?

Melaena happens when you bleed somewhere inside your digestive system, usually your stomach or the top part of your small bowel (duodenum). As the blood passes through your gut, it's changed by digestive juices and bacteria, which is what gives your stool its dark colour and strong smell.

Common causes include:

a bleeding stomach or duodenal ulcer, often linked to painkillers called non-steroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen), steroid medicines, or an infection called Helicobacter pylori (H pylori)
inflammation of your stomach lining (gastritis) or your gullet (oesophagitis)
swollen, fragile veins in your gullet or stomach (oesophageal varices), usually linked to liver disease
a tear in your gullet caused by forceful vomiting or retching (a Mallory-Weiss tear)
cancer of the stomach, gullet or pancreas
blood-thinning medicines (anticoagulants), which can make any of the above bleed more easily.

Less often, melaena is caused by a bulging pouch in the small bowel (Meckel's diverticulum), a small bowel tumour, abnormal blood vessels in the gut, a blood disorder that affects clotting, or a severe viral infection that causes bleeding.

Are there different types of melaena?

Melaena is not usually divided into formal types, but two things are worth understanding. First, not everything that turns your stool black is melaena: iron tablets, some indigestion medicines containing bismuth, activated charcoal, and dark foods such as black pudding, liquorice or blueberries can all cause black stools without any bleeding. True melaena has a distinctive tarry texture and strong smell that these other causes don't usually produce.

Second, melaena almost always comes from bleeding high up in your digestive system, in your stomach, gullet, or the top of your small bowel. Very occasionally, slow bleeding lower down, such as in the right side of your large bowel, can also cause melaena, because the blood has time to break down as it passes through.

How is melaena diagnosed?

If you see a doctor about melaena, they'll usually ask about your medicines, any history of stomach problems, and how much alcohol you drink, since these all help point to a likely cause. They may also examine your back passage (rectum) with a gloved finger to confirm the stool is genuinely black and tarry.

You'll usually have blood tests to check your general health, how much blood you may have lost, and how well your blood is clotting. A stool sample may also be checked for hidden blood.

The main test used to find the source of bleeding is an endoscopy, sometimes called a gastroscopy, where a doctor passes a thin, flexible tube with a camera down your throat and into your stomach to look for the cause and, in some cases, treat it at the same time. If this doesn't give an answer, you may be offered a CT scan (a detailed X-ray scan), sometimes with a dye injected into your blood vessels, or a camera test of your large bowel called a colonoscopy.

How is melaena treated?

Treatment aims to replace any blood you've lost, stop the bleeding, and treat whatever is causing it. If you've lost a lot of blood, you may need fluids through a drip or a blood transfusion, and any problems with your blood clotting will be corrected too.

Once the cause is found, treatment usually depends on what it is:

bleeding ulcers are usually treated during the endoscopy itself, using heat or an injection to seal the bleeding vessel, followed by acid-suppressing medicines called proton pump inhibitors (PPIs) to help the area heal
bleeding varices need urgent endoscopy to band or seal the swollen veins, alongside medicines to reduce blood flow to the gut and antibiotics; a special tube can be used temporarily to control severe bleeding if needed
cancer-related bleeding is managed with a biopsy to confirm the diagnosis, followed by a surgical and oncology (cancer care) treatment plan.

When should I see a doctor?

Melaena always needs medical assessment, since it's a sign of bleeding inside your body that may still be ongoing, even if it started a few days ago. Contact a doctor as soon as you notice black, tarry, strong-smelling stools.

Get emergency care straight away if you also have:

vomiting blood, or vomit that looks like coffee grounds
dizziness, weakness, faintness or lightheadedness
a racing heartbeat or shortness of breath
severe tummy pain
melaena that lasts more than a day or two.

FAQs

What's the difference between melaena and just black stools?

Not all black stools mean you're bleeding. Iron tablets, bismuth-containing medicines, activated charcoal, and some foods can all turn stools black without any blood being present. True melaena is tarry and sticky, with a distinctly strong, unpleasant smell that these other causes don't usually produce.
How much blood loss causes melaena?

Around 50 to 70ml of blood can turn your stool black. Either way, melaena is a sign that a genuine amount of bleeding has taken place.
Does melaena mean I'm still bleeding right now?

Not necessarily. Blood can take a few days to pass through your gut, so the black stool you see may reflect bleeding that has already stopped. There's no way to be sure without medical assessment though, so you shouldn't assume the bleeding has stopped on its own.
Which doctor should I see for melaena?

A doctor who specialises in the digestive system, called a gastroenterologist, usually manages the underlying cause of melaena. If you're in the middle of an urgent bleed, an emergency department is the right place to go instead.
Can I treat melaena at home?

No. Melaena needs proper medical evaluation to find and treat the source of bleeding, so it isn't something to manage by yourself.
Can melaena be prevented?

Some causes can be reduced by taking medicines as prescribed, drinking alcohol in moderation, and getting ongoing conditions such as ulcers or liver disease properly managed. This won't prevent every case, but it lowers your risk.