Gastroscopy vs colonoscopy: upper or lower gut camera test?

Upper gut symptoms such as persistent indigestion, difficulty swallowing, upper abdominal pain, repeated vomiting or vomiting blood point toward gastroscopy. Lower gut symptoms such as blood in the stool, a persistent change in bowel habit, or a positive bowel screening test point toward colonoscopy.

Some symptoms are less specific. Unexplained iron-deficiency anaemia, weight loss, or anaemia with gut symptoms may need both, because the bleeding or malabsorption could arise from either end.

After fasting, you are given a throat anaesthetic spray, sedation, or both. A flexible tube a little wider than a pencil is passed through the mouth while you lie on your side. The doctor looks at the lining, can take biopsies (for example to check for coeliac disease, H. pylori or inflammation) and can treat some problems such as bleeding. It usually takes a short time, and you can go home after recovering from sedation.

Common after-effects are a sore throat and bloating. Serious complications such as perforation or bleeding are uncommon but are discussed during consent.

Colonoscopy needs thorough bowel cleansing with laxatives, because residue hides polyps and small cancers. A flexible camera is passed through the rectum and advanced around the colon, with air or carbon dioxide used to open the bowel. Sedation or pain relief is commonly offered. Polyps can be removed and biopsies taken during the same test.

It takes longer than gastroscopy and has a higher rate of bloating and cramping afterwards. Risks include bleeding after polyp removal and, rarely, perforation. A poor bowel preparation can mean the test is incomplete and needs to be repeated.

NICE suspected cancer guidance (NG12) sets out symptom combinations that trigger urgent endoscopy or other investigations, for example difficulty swallowing in any age or upper abdominal symptoms in older people with weight loss for gastroscopy, and certain bowel symptoms or iron-deficiency anaemia for lower gut tests. The choice follows the symptom pattern and the risk, not patient preference.

For people with low-risk bowel symptoms, a faecal immunochemical test (FIT) is often used first to decide whether colonoscopy is needed, a pathway recommended by NICE diagnostics guidance.

• Heartburn or indigestion for weeks despite treatment, difficulty swallowing, or vomiting blood: gastroscopy via your GP or specialist; vomiting blood is an emergency (999).

• Blood in the stool or a persistent change in bowel habit: GP assessment, FIT test or urgent colonoscopy as per the pathway.

• Iron-deficiency anaemia with no obvious cause: often both tests, led by the gastroenterologist.

• Positive NHS bowel screening result: colonoscopy through the screening programme.

• Symptoms are mild and recent: your GP may try treatment or a test first.

Gastroscopy does not examine the bowel, and colonoscopy does not examine the stomach, so one cannot replace the other. A clear gastroscopy does not rule out a bowel cause for anaemia.

Another misconception is that sedation means you will be unconscious. It is usually conscious sedation, in which you are relaxed and drowsy, and many people remember little.