Endoscopy can detect a wide range of diseases, from acid reflux and stomach ulcers to cancers of the digestive tract, lungs, and bladder. The specific conditions found depend on which type of endoscopy is performed and where the camera is directed. Most people asking this question are facing an upcoming procedure or wondering whether endoscopy might explain their symptoms, so here’s a thorough look at what these procedures can find.
Upper GI Endoscopy: Esophagus, Stomach, and Small Intestine
The most common type of endoscopy is an upper GI endoscopy (also called an EGD), where a thin, flexible tube with a camera is passed through the mouth to examine the esophagus, stomach, and the first part of the small intestine. This single procedure can detect a surprisingly long list of conditions:
- Acid reflux (GERD) and the inflammation it causes in the esophagus (esophagitis)
- Stomach and duodenal ulcers (peptic ulcers)
- Barrett’s esophagus, a precancerous change in the lining of the esophagus caused by chronic acid exposure
- Celiac disease, confirmed through small biopsies of the intestinal lining
- Crohn’s disease affecting the upper digestive tract
- Gastritis and duodenitis (inflammation of the stomach or upper intestine)
- Hiatal hernia, where part of the stomach pushes up through the diaphragm
- Cancerous and noncancerous tumors of the esophagus, stomach, or duodenum
- Swallowing disorders caused by narrowing or structural changes
- Signs of liver cirrhosis and portal hypertension, including swollen veins in the esophagus (varices)
During the procedure, your doctor can take small tissue samples (biopsies) from anything that looks abnormal. These biopsies are often what clinch the diagnosis. A suspicious-looking ulcer, for example, may turn out to be benign once the tissue is examined under a microscope, or it may reveal early cancer cells that wouldn’t have been caught any other way.
How Endoscopy Detects Celiac Disease
Celiac disease is one of the most important diagnoses made through upper endoscopy. Blood tests can suggest the condition, but a biopsy of the small intestine showing damage to the tiny finger-like projections (villi) that absorb nutrients remains the gold standard for confirming it. Pathologists grade the damage on a scale from 0 to 3, with grade 3 representing the classic flattened villi strongly characteristic of celiac disease. Lower grades of damage can be suggestive but aren’t enough on their own to confirm the diagnosis without supporting blood work.
Taking more biopsy samples from different spots in the small intestine increases accuracy, since the damage can be patchy. If your doctor suspects celiac disease, you’ll typically need to keep eating gluten in the weeks before the procedure so the damage is visible.
Barrett’s Esophagus and Cancer Surveillance
People with long-standing acid reflux sometimes develop Barrett’s esophagus, where the normal lining of the lower esophagus is replaced by tissue that resembles the intestinal lining. This matters because Barrett’s can, over years, progress toward esophageal cancer. Endoscopy is the only reliable way to detect it.
Once Barrett’s is found, the American Gastroenterological Association recommends ongoing surveillance endoscopies to watch for precancerous changes. If the affected segment is very small (less than 1 cm), surveillance generally isn’t needed. For longer segments without precancerous changes, periodic repeat endoscopies with structured biopsies are recommended. The goal is catching any progression early, when it can still be treated with minimally invasive techniques rather than major surgery.
Colonoscopy: Polyps, Cancer, and Inflammatory Disease
Colonoscopy examines the entire large intestine and rectum. It’s the primary screening tool for colorectal cancer, and the U.S. Preventive Services Task Force recommends starting screening at age 45, with repeat colonoscopies every 10 years if results are normal. The conditions it detects include colon and rectal polyps (some of which are precancerous), colorectal cancer, inflammatory bowel disease, diverticular disease, and infections causing colitis.
A related procedure, flexible sigmoidoscopy, examines only the lower portion of the colon. It can show irritated or swollen tissue, ulcers, polyps, and cancer in that area. If anything abnormal turns up during a sigmoidoscopy, your doctor will typically recommend a full colonoscopy to check the rest of the colon.
What makes colonoscopy particularly valuable is that it’s both diagnostic and therapeutic. If a polyp is found, the doctor can remove it during the same procedure, eliminating it before it ever has a chance to become cancerous.
Distinguishing Crohn’s Disease From Ulcerative Colitis
Endoscopy plays a critical role in differentiating the two main types of inflammatory bowel disease. Both Crohn’s disease and ulcerative colitis cause inflammation in the digestive tract, but they look distinctly different through the camera, and telling them apart affects treatment.
Ulcerative colitis almost always involves the rectum and spreads continuously upward. The inflammation stays in the surface lining and doesn’t skip around. Crohn’s disease, by contrast, tends to appear in patches with normal tissue in between, frequently involves the area where the small intestine meets the colon, and causes deeper ulceration. Characteristic signs of Crohn’s include long ulcers (4 to 5 cm or more), a cobblestone-like texture of the intestinal wall, and small shallow ulcers. In one study of newly diagnosed Crohn’s patients, about 59% had these small ulcers, 37% had long ulcers, and 24% had the cobblestone pattern.
Crohn’s also causes complications that ulcerative colitis does not: narrowing of the intestine (strictures), abnormal tunnels between organs (fistulas), and disease around the anus. Biopsies taken during endoscopy can add supporting evidence, though a hallmark microscopic feature of Crohn’s appears in only 13% to 36% of cases, making it a helpful but imperfect clue.
Infections Found Through Endoscopy
Endoscopy can identify infections throughout the digestive tract that blood tests or imaging might miss. The most common is H. pylori, a bacterium that causes stomach ulcers and gastritis, routinely detected through biopsies taken during upper endoscopy.
In people with weakened immune systems, endoscopy can reveal viral infections like cytomegalovirus or fungal infections in the esophagus. Biopsies allow the lab to identify the specific organism causing the problem. Specialized endoscopic ultrasound with needle biopsy has also diagnosed less common infections, including tuberculosis, histoplasmosis (a fungal infection common in the Mississippi and Ohio River Valleys), and actinomycosis. These infections can form masses that mimic cancer on imaging, so the biopsy is essential to avoid unnecessary surgery.
Bile Duct and Pancreatic Conditions
Two specialized forms of endoscopy focus on the bile ducts and pancreas. ERCP (endoscopic retrograde cholangiopancreatography) threads a scope through the mouth and into the small intestine, then injects dye into the bile and pancreatic ducts to visualize blockages. Endoscopic ultrasound (EUS) combines endoscopy with ultrasound imaging to get detailed views of the pancreas, bile ducts, and surrounding structures.
Together, these procedures detect gallstones lodged in the bile duct, bile duct blockages from tumors, pancreatic cancer, chronic pancreatitis, pancreatic cysts, and autoimmune pancreatitis. EUS is particularly useful because it can take needle biopsies of masses in the pancreas or bile duct, helping determine whether a suspicious growth is cancerous or caused by something treatable like autoimmune inflammation. This distinction matters enormously, since autoimmune pancreatitis responds well to steroids and doesn’t require the major surgery that cancer does.
Beyond the Digestive Tract
Endoscopy isn’t limited to the gut. The same principle of passing a camera into the body applies to several other organ systems.
Bronchoscopy examines the airways and lungs. It can diagnose lung cancer, bacterial and viral pneumonias, tuberculosis, fungal infections, sarcoidosis, lung damage from autoimmune conditions like rheumatoid arthritis, and narrowing of the airways. It’s also used after lung transplants to check for organ rejection.
Cystoscopy looks inside the bladder and urethra, detecting bladder cancer, bladder stones, chronic inflammation, and structural abnormalities that cause urinary problems. Arthroscopy lets surgeons visualize the inside of a joint to diagnose cartilage tears, ligament damage, and inflammatory joint conditions. Hysteroscopy examines the inside of the uterus to find polyps, fibroids, and structural causes of abnormal bleeding.
How AI Is Improving Detection Rates
One of the biggest recent advances in endoscopy is the use of artificial intelligence to help doctors spot abnormalities they might otherwise miss. During colonoscopy, AI systems analyze the video feed in real time and highlight areas that look like polyps.
A meta-analysis of randomized trials found that AI-assisted colonoscopy detected significantly more precancerous growths (adenomas) than standard colonoscopy across all sizes. For the smallest growths (5 mm or less, which are the easiest to overlook), AI found them in 26.2% of patients compared to 18.6% with conventional methods. That translates to about 80 additional patients out of every 1,000 who had a precancerous polyp caught and removed. For medium-sized growths (6 to 9 mm), AI added 24 more detections per 1,000 patients. Even for larger growths, detection improved by about 13 per 1,000. These numbers are meaningful because every adenoma caught and removed is one that can’t progress to colon cancer.