Endoscopy — Purpose, Procedure & Normal Values | MyMedicPlus

Endoscopy is a family of minimally invasive procedures in which a thin, flexible instrument called an endoscope — incorporating a high-definition fibre-optic or electronic camera, a light source, and one or more working channels — is advanced through a natural body orifice to directly visualise the interior lining of hollow organs or body cavities. Upper gastrointestinal (GI) endoscopy — known as gastroscopy or oesophago-gastro-duodenoscopy (OGD) — examines the oesophagus, stomach, and proximal small intestine (duodenum) to the level of the ligament of Treitz. Lower GI endoscopy encompasses colonoscopy (full examination of the colon and terminal ileum) and flexible sigmoidoscopy (left colon to the splenic flexure). Capsule endoscopy uses a swallowed wireless camera to image the entire small bowel. Beyond diagnosis, endoscopy is simultaneously therapeutic: haemostasis of bleeding peptic ulcers (adrenaline injection, clips, heater probe), oesophageal or colonic polypectomy using snare or forceps, oesophageal dilation, variceal band ligation, stent placement for malignant strictures, and endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD) of early cancers can all be accomplished during a single endoscopic session without open surgery.

Upper GI endoscopy (gastroscopy) is ordered to investigate persistent dyspepsia or heartburn (GORD/GERD) unresponsive to treatment, progressive dysphagia (difficulty swallowing), odynophagia (painful swallowing), unexplained upper abdominal pain, haematemesis (vomiting blood), melaena (black tarry stools from upper GI bleeding), iron-deficiency anaemia in men and postmenopausal women, and unexplained weight loss. It establishes diagnoses including peptic ulcer disease, H. pylori gastritis (biopsy-based CLO test), Barrett's oesophagus and its surveillance, oesophageal and gastric cancer, coeliac disease (duodenal biopsies showing villous atrophy), and portal hypertension with oesophageal varices. Colonoscopy is the gold standard for colorectal cancer screening (in average-risk individuals from age 45–50) and polyp removal, investigation of fresh rectal bleeding (haematochezia), change in bowel habit persisting over four weeks, iron-deficiency anaemia, abdominal mass, or positive faecal immunochemical test (FIT). It diagnoses colorectal cancer, adenomatous polyps (precancerous), inflammatory bowel disease — Crohn's disease (segmental transmural granulomatous inflammation) and ulcerative colitis (continuous mucosal colitis from the rectum) — ischaemic colitis, and diverticular disease.

For upper GI endoscopy (gastroscopy): fast completely — no food, milk, or opaque fluids — for at least 6 hours before the procedure. Clear water may be consumed until 2 hours before. Stop proton pump inhibitors (PPIs) for 2 weeks before any test for H. pylori. For colonoscopy: follow a low-residue or low-fibre diet for 1–3 days before the procedure, avoiding seeds, nuts, and high-fibre vegetables. Take the prescribed bowel preparation solution (polyethylene glycol — Moviprep, Klean-Prep — or sodium picosulphate — Picolax) according to your unit's schedule, typically split between the evening before and the morning of the procedure, to achieve complete colonic cleansing (clear stool output confirms adequate preparation). Stop iron supplements 5–7 days before colonoscopy, as iron causes black staining of the colonic mucosa that obscures mucosal detail. Blood thinners (warfarin, direct oral anticoagulants, clopidogrel) may need to be paused — seek specific advice from your endoscopist for your individual anticoagulation indication and procedure bleeding risk. Inform the team of diabetes medications: insulin and sulfonylureas should be dose-adjusted on the day of fasting; SGLT2 inhibitors should be held 3 days before. Arrange a driver, as intravenous sedation is routinely administered and you cannot drive for 24 hours afterwards.

An intravenous cannula is inserted in your forearm before the procedure for administering sedation and any emergency drugs. For gastroscopy, you lie on your left side with a protective plastic mouthguard between your teeth to protect the endoscope and prevent you from biting down. After sedation is given (typically midazolam 2–5 mg with or without fentanyl 25–50 mcg), the endoscopist passes the lubricated slim endoscope gently over the tongue, past the epiglottis, through the cricopharyngeal sphincter (upper oesophageal sphincter) at approximately C5 vertebral level, down the oesophagus, through the lower oesophageal sphincter, into the stomach (retroflexing in the fundus to visualise the gastro-oesophageal junction from below), and into the duodenal bulb and second part of the duodenum. For colonoscopy, you lie on your left side and the colonoscope is introduced through the anal canal and advanced under direct vision around the sigmoid colon, descending colon, splenic flexure, transverse colon, hepatic flexure, ascending colon, and into the caecum — confirmed by identifying the ileocaecal valve and appendix orifice. Carbon dioxide insufflation (preferred over air for faster absorption and less post-procedure bloating) opens the lumen for visualisation. Biopsies, snare polypectomy, or haemostasis are performed through the working channel during withdrawal. Most patients experience only mild bloating; sedation prevents significant distress.

The endoscopist provides a verbal summary of key findings immediately after the procedure while you recover from sedation. A formal written endoscopy report is generated within 1–2 days, and a copy may be provided before you leave the unit. Endoscopic findings are described using standardised terminology by anatomical location: normal pink, glistening mucosa with a regular vascular pattern (normal); erythema, oedema, or loss of vascular pattern (non-specific inflammation); linear erosions or ulcers classified by the Los Angeles (oesophagus), Forrest (peptic ulcer bleeding), or Paris classifications (polyp morphology); polyps recorded by size (in millimetres), morphology (pedunculated, sessile, flat or depressed), and location in the colon using the Paris classification. Cancer is documented by size, morphology, extent of spread within the visible lumen, and biopsy is taken. Biopsy histology — sent in formalin to the pathology laboratory — typically returns in 7–14 working days. CLO (Campylobacter-like organism) test results for H. pylori are available in 60 minutes. A normal endoscopy does not exclude functional GI disorders (irritable bowel syndrome, functional dyspepsia) in which the mucosa appears endoscopically normal despite significant symptoms. Your gastroenterologist will discuss all results and management implications at a follow-up appointment or through a letter copied to your GP.

Endoscopy has an excellent safety profile when performed in a properly equipped and staffed unit by trained endoscopists. Minor expected after-effects include abdominal bloating and cramping from insufflated gas (resolves within 2–4 hours), mild sore throat after gastroscopy lasting 1–2 days, and brief soreness at the IV cannula site. Serious complications are rare but include: perforation of the GI tract (gastroscopy rate approximately 1 in 10,000; colonoscopy without intervention 1 in 1,000; colonoscopy with polypectomy 1 in 500), post-polypectomy bleeding (~1% of polypectomies, usually managed endoscopically), aspiration pneumonia from regurgitated gastric contents during gastroscopy (rare with appropriate fasting), and sedation-related cardiorespiratory depression (monitored continuously by a dedicated recovery nurse with supplemental oxygen available). All patients must remain under observation until sedation has worn off before discharge. Patients must not drive for 24 hours, operate machinery, or make legal decisions on the day of sedation. Colonoscopy has a known adenoma miss rate of 6–27% for polyps smaller than 10 mm, dependent on bowel preparation quality (inadequate prep is the single largest avoidable determinant of miss rate), endoscopist withdrawal time (minimum 6 minutes recommended), and mucosal visualisation technique. A colonoscopy with excellent bowel preparation, high adenoma detection rate (ADR) quality indicator, and adequate withdrawal time provides the most reliable examination but cannot guarantee detection of all small or flat lesions.