Quick Answer
Diagnostic endoscopy uses the endoscope to visualise the gastrointestinal tract and identify pathology — its output is a finding and a report. Therapeutic endoscopy uses the same instrument to treat what has been found — its output is an intervention. The distinction matters clinically because therapeutic procedures require additional skills, equipment, dedicated time, specialist backup, and in many cases a higher-acuity facility. Most referrals from general practice and general medicine are for diagnostic endoscopy; the decision to escalate to therapeutic endoscopy is usually made after the diagnostic findings are known.
Every doctor who manages GI patients refers for endoscopy. Not every doctor who refers understands precisely what they are requesting — or when diagnostic endoscopy alone is insufficient and therapeutic capability becomes the clinical requirement.
That gap matters in practice. A referral that should specify urgent therapeutic endoscopy capability such as an acute upper GI bleed is not the same referral as a routine diagnostic OGD for dyspepsia. Sending the wrong referral to the wrong setting delays definitive management.
This article is for general physicians, surgeons, and family medicine doctors who refer GI patients for endoscopy but want a clearer clinical framework for the referral decision. Doctors who want to extend their own endoscopy knowledge beyond the referral level can explore MGA’s Fellowship in GI Endoscopy.
What this article covers
- Defining diagnostic endoscopy: what it is, what it does
- Defining therapeutic endoscopy: what distinguishes it
- Upper GI: diagnostic indications vs therapeutic triggers
- Lower GI: diagnostic indications vs therapeutic triggers
- The overlap problem — procedures that start diagnostic and become therapeutic
- Referral thresholds: what to specify when you refer
- Frequently asked questions
Defining diagnostic endoscopy: what it is, what it does
Diagnostic endoscopy is the use of a flexible endoscope to directly visualise a segment of the gastrointestinal tract. Its purpose is to find, characterise, and document pathology. The endoscopist looks, biopsies if indicated, and reports findings. No therapeutic intervention is performed during the procedure itself.
The output of a diagnostic endoscopy is information: the mucosal appearance at sites examined, the presence and characteristics of lesions, and the correlation of visual findings with the clinical question that prompted the referral. That information then guides the management decision — which may include a separate therapeutic procedure, medical treatment, surveillance, or discharge.
Diagnostic endoscopy encompasses upper GI endoscopy (OGD) for oesophageal, gastric, and duodenal evaluation, and colonoscopy or flexible sigmoidoscopy for colonic and terminal ileal evaluation. Capsule endoscopy used for small bowel evaluation is diagnostic only.
Defining therapeutic endoscopy: what distinguishes it
Therapeutic endoscopy — also called interventional endoscopy or operative endoscopy — uses the same endoscopic access to treat pathology rather than only identify it. An instrument passed through the working channel of the endoscope performs the therapeutic action while the endoscopist maintains visual control.
What distinguishes therapeutic from diagnostic endoscopy in practical terms is not just the procedure performed — it is the requirement set that surrounds the procedure.
Diagnostic endoscopy requires
- Endoscopist with scoping competence
- Standard endoscopy unit setup
- Conscious sedation or no sedation
- Basic monitoring
- Biopsy forceps if sampling needed
Therapeutic endoscopy additionally requires
- Endoscopist trained in specific therapeutic technique
- Additional accessories — clips, snares, balloons, cautery
- Higher-acuity monitoring and backup
- Surgical backup availability for complications
- Often: anaesthesia support for deeper sedation
This distinction has direct relevance to referral — a facility capable of diagnostic endoscopy is not automatically capable of therapeutic endoscopy. Referring an acute upper GI bleed to a unit without haemostatic capability is a clinical mismatch that delays treatment.
Upper GI endoscopy: diagnostic indications vs therapeutic triggers
When diagnostic OGD is appropriate
| Indication | What you are looking for | Priority |
|---|---|---|
| Dyspepsia with alarm symptoms | Malignancy, ulcer, Barrett’s oesophagus | Urgent — within 2 weeks |
| Unexplained dysphagia | Malignancy, stricture, motility disorder | Urgent |
| Unexplained iron-deficiency anaemia | Upper GI source of chronic blood loss | Elective to semi-urgent |
| Suspected peptic ulcer disease | Active ulcer, H. pylori status, healing | Elective to semi-urgent |
| Persistent vomiting without explanation | Gastric outlet obstruction, mucosal pathology | Semi-urgent |
| Surveillance — Barrett’s oesophagus | Dysplasia surveillance | Elective (interval-based) |
When the therapeutic threshold is triggered in upper GI
| Clinical Scenario | Therapeutic Procedure Required | Facility Requirement |
|---|---|---|
| Active upper GI haemorrhage | Endoscopic haemostasis — adrenaline injection, thermal coagulation, haemostatic clips | Therapeutic unit with anaesthesia and surgical backup |
| Peptic ulcer with high-risk appearance | Haemostatic therapy (dual modality preferred) | Therapeutic unit — urgent |
| Oesophageal or gastric varices with active bleeding | Band ligation (oesophageal), injection sclerotherapy (gastric) | Specialist GI unit with variceal expertise |
| Oesophageal stricture causing dysphagia | Balloon or bougie dilation | Therapeutic endoscopy unit |
| Biliary obstruction (suspected CBD stone, cholangitis) | ERCP with sphincterotomy and stone extraction | ERCP-capable centre — specialist procedure |
Lower GI endoscopy: diagnostic indications vs therapeutic triggers
When diagnostic colonoscopy is appropriate
| Indication | What you are looking for | Priority |
|---|---|---|
| Rectal bleeding (no obvious anorectal source) | Colorectal malignancy, polyps, IBD, angiodysplasia | Urgent to semi-urgent by age and features |
| Altered bowel habit, unexplained | Colorectal malignancy, IBD | Semi-urgent if alarm features present |
| Unexplained iron-deficiency anaemia | Right-sided colonic malignancy, angiodysplasia | Semi-urgent |
| Positive faecal occult blood test | Adenomatous polyp, early colorectal malignancy | Within 4–6 weeks |
| Known or suspected IBD | Disease extent, activity, biopsy for histology | Elective to semi-urgent |
| Surveillance — previous polyp or malignancy | Recurrence, new polyps | Elective (interval-based) |
When the therapeutic threshold is triggered in lower GI
| Clinical Scenario | Therapeutic Procedure Required | Key Consideration |
|---|---|---|
| Colonic polyp identified on diagnostic colonoscopy | Snare polypectomy or EMR depending on polyp size and morphology | May be performed in same sitting or listed for separate therapeutic session |
| Lower GI haemorrhage from angiodysplasia | Thermal coagulation, haemostatic clips, injection | Requires therapeutic capability — urgent referral |
| Colonic stricture | Balloon dilation or stenting | Specialist therapeutic endoscopy unit |
The overlap problem: procedures that start diagnostic and become therapeutic
One of the most practically important aspects of this distinction is that many procedures that begin as diagnostic become therapeutic intraoperatively.
Example 1: A patient referred for diagnostic OGD for dyspepsia is found on scoping to have a gastric ulcer with a visible vessel — a high-risk stigmatum for rebleeding. Immediate haemostatic therapy is indicated. If the facility does not have haemostatic equipment available at the time of diagnostic scoping, the endoscopic opportunity is lost.
Example 2: A patient referred for colonoscopy to investigate rectal bleeding is found to have a 15mm sessile polyp. Same-session polypectomy is appropriate — but requires snare equipment and the endoscopist’s polypectomy training. If the unit is set up only for diagnostic colonoscopy, the patient goes home and needs a second procedure booking.
The clinical implication for the referring doctor is: when there is a meaningful probability that the diagnostic procedure will reveal a finding requiring therapeutic intervention, the referral should specify a facility with therapeutic capability. For any upper GI bleed referral, therapeutic capability should always be assumed necessary.
Referral thresholds: what to specify when you refer
| Referral Scenario | Urgency | Therapeutic Capability Needed? |
|---|---|---|
| Active upper GI haemorrhage | Emergency — same day | Yes — haemostatic unit essential |
| Suspected peptic ulcer, haemodynamically stable, melena | Urgent — within 24 hours | Likely — request therapeutic unit |
| Oesophageal varices — elective banding | Planned | Yes — variceal banding programme |
| Dyspepsia with alarm symptoms | 2 weeks | No — standard diagnostic unit appropriate |
| Colorectal polyp surveillance | Elective | Preferred — mention if high-risk polyp history |
| Suspected CBD stone with cholangitis | Urgent — within 24–48 hours | Yes — ERCP-capable centre only |
| IBD assessment — elective | Elective | No — standard diagnostic unit appropriate |
A note on ERCP: ERCP is a specialist therapeutic procedure that requires dedicated equipment, advanced endoscopy training, and fluoroscopy. It should never be referred to a general diagnostic endoscopy unit. Referrals for suspected biliary obstruction, cholangitis, or pancreatic duct pathology requiring ERCP should be directed explicitly to centres with confirmed ERCP capability and a dedicated biliary endoscopist.
Doctors who perform or supervise GI endoscopy: explore MGA’s Fellowship in GI Endoscopy
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Frequently asked questions
What is the main difference between diagnostic and therapeutic endoscopy?
Diagnostic endoscopy uses the endoscope to visualise the GI tract and identify pathology — the procedure produces a finding and a report. Therapeutic endoscopy uses the same endoscopic access to treat what has been found — the procedure produces an intervention. Therapeutic endoscopy requires additional technical skills, specialised equipment, and typically a higher-acuity clinical environment than diagnostic endoscopy alone.
Can a diagnostic endoscopy become therapeutic in the same session?
Yes — and this is one of the most practically important aspects of the distinction. A diagnostic OGD that identifies a bleeding vessel in a peptic ulcer, or a diagnostic colonoscopy that finds a large polyp, may transition to a therapeutic procedure in the same sitting if the facility and endoscopist have the required capability. Referrals where there is a meaningful chance of therapeutic intervention should specify a unit with therapeutic capability.
When does upper GI bleeding require therapeutic endoscopy?
Any upper GI bleed presenting with haematemesis, haemodynamic compromise, or endoscopic features of high rebleeding risk requires therapeutic endoscopic haemostasis, not just diagnostic evaluation. These patients should be referred directly to a unit with confirmed haemostatic capability, anaesthesia support, and surgical backup.
What does ERCP stand for and when is it indicated?
ERCP stands for endoscopic retrograde cholangiopancreatography. It is a therapeutic and diagnostic endoscopic procedure used to access the biliary and pancreatic duct systems. Common indications include suspected common bile duct stones, biliary obstruction causing cholangitis or jaundice, and selected cases of pancreatic duct pathology. It is a specialist procedure requiring specific training, equipment, and fluoroscopy — it should only be referred to ERCP-capable centres.
Is polypectomy always done in the same colonoscopy session as polyp detection?
It depends on polyp size, morphology, bowel preparation quality, patient factors, and the facility’s therapeutic capability at the time. Small pedunculated polyps are typically removed in the same session. Larger, sessile, or complex polyps may be removed in the same session at a therapeutic-capable unit, or may be listed for a planned separate therapeutic colonoscopy. This is an endoscopist and clinical decision — not a fixed protocol.
Medical Global Academy — Editorial Team
This article is produced for educational purposes by MGA’s academic team and is intended for qualified medical professionals. It provides a clinical framework for understanding the endoscopy referral decision and does not constitute clinical guidelines or replace institutional protocols. Last reviewed: August 2026.