Gastroscopy: why it is done, how to prepare and what to expect

A gastroscopy is a type of endoscopy. A long flexible tube, the gastroscope, carries a light and a tiny camera and is passed through the mouth (or sometimes the nose) and down the throat. Cancer Research UK notes that the test may also be called an endoscopy or an oesophago-gastro-duodenoscopy (OGD), and that it is usually done in the endoscopy department of a hospital by a doctor or specialist nurse called an endoscopist.

The images appear on a screen, so the endoscopist can see the lining of the food pipe, stomach and the first part of the small intestine (the duodenum). Tissue samples can be taken through the tube and sent to a laboratory, where a pathologist examines them under a microscope.

The NHS groups the reasons into checking what is causing digestive symptoms, treating problems found in the digestive system, and checking for some types of cancer such as stomach or oesophageal cancer. Cancer Research UK gives a longer list of symptoms that can lead to the test. A referral does not mean that something serious has been found: for many people, the NHS says, a gastroscopy will not find anything to worry about.

• Indigestion or heartburn that does not go away with medicines or keeps coming back.

• Difficulty or pain when swallowing.

• Losing weight without trying.

• Regularly feeling or being sick, or having blood in vomit.

• Blood in the poo or passing black poo.

• Low iron levels (iron deficiency anaemia) or abnormal bleeding.

• Regular surveillance if you have Barrett's oesophagus, to check for changes in the cells of the oesophagus lining.

The NHS says you should receive a letter telling you when and where the procedure will take place, when to stop eating and drinking, about medicines you may be offered, and how long you may have to wait for results. Let the hospital know if you are pregnant. Bring details of the medicines you take and follow the hospital's instructions about them.

Cancer Research UK says you may have blood tests beforehand to check your blood levels and how well your blood clots, and that you should tell your doctor if you take blood-thinning medicines such as warfarin, aspirin, clopidogrel, apixaban, rivaroxaban or ticagrelor. You may be told to stop some of them, and some indigestion medicines, for a while. People with diabetes should talk to their doctor if not eating could be a problem.

A nurse will check your medical history and allergies and Cancer Research UK says they check blood pressure, heart rate and oxygen levels. You remove glasses and any false teeth, and a plastic mouth guard protects your teeth. Cancer Research UK describes two ways of having the test.

The NHS says you may feel like you want to be sick as the tube passes, which should stop once the tube reaches the stomach, and that sedation can help prevent this. Air is pumped in to inflate the stomach, so you may feel bloated and burp a few times. If a biopsy is taken you will not feel anything. Cancer Research UK says the tube is slightly bigger than a pen and will be uncomfortable but should not be painful.

Afterwards you go to a recovery room. The NHS says that if you had sedation you will need someone to take you home and stay with you for 24 hours, and to avoid alcohol, driving, operating machinery and signing important documents during that time. Some stomach and throat pain afterwards is normal and should pass in a few hours.

The NHS calls gastroscopy common and straightforward, with rare complications that can include a reaction to the sedation, bleeding in the stomach and infection. Cancer Research UK also lists a sore throat lasting a few days, a small chance of damage to teeth, a small risk of breathing in secretions, and a very small risk of a tear (perforation) that might need an operation.

The NHS says to call 111, or the hospital where you had the gastroscopy, if you develop a high temperature or feel hot, cold or shivery, or have dark, tar-like poo. It says to call 999 or go to A&E if you keep being sick, are vomiting blood, are short of breath, or have severe stomach or chest pain, or pain that gets worse. Do not drive yourself to A&E.

You may be told something about what was seen before you leave. The NHS says a doctor or nurse may explain the results, and that you may be given a follow-up appointment to discuss your results and possible treatments. Cancer Research UK says biopsy results should arrive within 1 to 2 weeks but may take longer, and suggests contacting the doctor who arranged the test if you have not heard after a couple of weeks.

If cancer is found, the NHS says you will be put in touch with a specialist cancer care team. The NHS also notes that for many people a gastroscopy will not find anything to worry about. Waiting for results can be worrying, and the NHS points to Cancer Research UK, Macmillan Cancer Support and Maggie's for support.

On the NHS a gastroscopy is arranged after a GP or hospital referral, and the timing depends on how urgent your symptoms are judged to be. Private endoscopy units offer the same test, often with more flexible appointments. The procedure, sedation options and risks are broadly the same. Whichever route you take, ask how and when you will get biopsy results and who will explain them.