What Is a Duodenal Biopsy and Why Is It Performed?

A duodenal biopsy is a small tissue sample taken from the lining of the duodenum, the first stretch of your small intestine just past the stomach, during an upper endoscopy. A gastroenterologist threads a thin, flexible tube with a camera down your throat and snips off tiny pieces of tissue using built-in forceps. Those samples go to a pathology lab, where they are examined under a microscope for signs of disease. The procedure is performed to diagnose or rule out a range of conditions, from celiac disease and parasitic infections to rare systemic illnesses and tumors, and its use has grown substantially over the past few decades.

How the Procedure Works

An upper gastrointestinal endoscopy, often called an EGD (esophagogastroduodenoscopy), is the vehicle for getting the biopsy. You fast beforehand, typically for at least six to eight hours. You are sedated, usually with a combination of a sedative and a pain reliever delivered through an IV, so the procedure is not painful. The endoscope passes through your mouth, down the esophagus, through the stomach, and into the duodenum. The entire exam usually takes around 15 to 20 minutes.

When the doctor reaches the duodenum, they use the endoscope’s forceps channel to clip small pieces of the mucosal lining. These tissue fragments are typically just a few millimeters across. They are placed in a preservative solution and sent to the pathology lab, where they are embedded in wax, sliced into extremely thin sections, placed on glass slides, and stained so their cellular structure becomes visible. The coordination between the gastroenterologist, the lab, and the pathologist matters a great deal: how the tissue is oriented on the slide, how many pieces are taken, and what stains are applied all affect whether the pathologist can make an accurate call.

Celiac Disease Is the Most Common Reason

The single biggest reason doctors order duodenal biopsies is to check for celiac disease, an autoimmune condition in which gluten triggers your immune system to attack the lining of the small intestine. Blood tests for antibodies (like anti-tissue transglutaminase) can strongly suggest celiac disease, but the biopsy remains the standard for confirming the diagnosis. The pathologist looks for a specific set of changes in the tissue, classified using the Marsh system, which describes a spectrum from mild immune-cell infiltration of the intestinal lining all the way to severe flattening of the finger-like projections called villi that normally absorb nutrients.¹

The growing recognition of celiac disease has driven a steep increase in how often duodenal biopsies are performed. One large retrospective study looking at over 13,000 upper endoscopies found that biopsies of the duodenum were taken in under 2% of procedures in the early 1990s but jumped to nearly 13% by the early 2000s.² That trend has only continued as awareness of the disease has expanded among both patients and clinicians.

How Many Biopsy Pieces Are Needed

If you are being evaluated for celiac disease, the number of tissue samples your doctor takes matters. The damage celiac disease causes is not always uniform; it can be patchy, affecting one area of the duodenum while leaving an adjacent spot relatively normal. A study that specifically addressed this question found that taking just two biopsy specimens caught about 90% of celiac cases, three specimens caught 95%, and four or more were needed for the rest.³ Most guidelines now recommend taking at least four samples from different spots in the duodenum, plus one or two from the duodenal bulb, to reduce the chance of a false negative.

This is worth knowing because if your doctor takes only one or two samples and the result comes back normal, that does not entirely rule out celiac disease. If your symptoms and blood work are strongly suggestive, a repeat biopsy with more samples might be warranted.

Misdiagnosis Goes Both Ways

A large referral-center study illustrates how tricky celiac diagnosis can be. Of 614 patients who arrived at a specialty clinic already carrying a celiac diagnosis from another institution, about 180 could not have that diagnosis confirmed after review. After thorough re-evaluation, only about a third of those 180 turned out to actually have celiac disease.⁴ That means a substantial number of people had been told they had celiac disease and were following a strict gluten-free diet when they did not need to be, while whatever was actually causing their symptoms went unaddressed.

Why does this happen? Part of the problem is that the microscopic changes seen in celiac disease, especially villous atrophy and increased immune cells in the lining, are not exclusive to celiac. Several other conditions produce a nearly identical picture under the microscope. This is why clinicians are supposed to combine the biopsy findings with blood-antibody results, symptoms, and response to a gluten-free diet before making a definitive diagnosis.

Drug-Induced Enteropathy and Celiac Lookalikes

One of the most striking celiac mimics is caused by a common blood-pressure medication. Olmesartan, a drug in the angiotensin-receptor blocker family, can trigger a condition that looks almost identical to celiac disease both clinically and under the microscope: diarrhea, weight loss, nausea, and duodenal biopsies showing villous atrophy with increased immune cells in the lining.⁵ The key difference is that celiac-antibody blood tests come back negative. A systematic review of reported cases found that nearly all patients had villous atrophy on biopsy, but only about two-thirds had the increased intraepithelial lymphocytes typically seen in celiac disease, and antibody testing was always negative.⁶

This is a case where the biopsy alone cannot tell the whole story. The pathologist sees villous damage and flags it, but without knowing the patient’s medication list, the finding might be mistakenly attributed to celiac disease. Stopping olmesartan typically resolves the problem, which itself becomes a diagnostic confirmation. If you are on an angiotensin-receptor blocker and develop chronic diarrhea and weight loss, this is something your doctor should consider before locking in a celiac diagnosis.

Infections and Parasites

Duodenal biopsies are also useful for detecting infections that take up residence in the small intestine. Giardia, a common waterborne parasite, is one example. Standard stool testing catches most cases, but in people with persistent or chronic diarrhea, stool microscopy misses a meaningful fraction. One study of patients with chronic diarrhea found that stool microscopy detected about 65% of Giardia infections, stool PCR caught an additional 27%, and duodenal biopsy PCR picked up the last 8% that both stool methods missed.⁷ The biopsy is rarely the first-line test for Giardia, but it serves as a safety net in stubborn cases.

In people with weakened immune systems, whether from HIV, organ-transplant medications, cancer chemotherapy, or chronic steroid use, a whole catalog of opportunistic infections can show up in duodenal tissue. Pathologists may encounter microsporidia, cryptosporidia, cyclospora, mycobacteria, adenovirus, and even fungi like cryptococcus. Recognizing these organisms on biopsy is a critical skill, because the infections they cause may not be obvious on imaging or blood tests, and treatment depends on identifying the specific organism.⁸

A pediatric study of routine duodenal biopsies found that among 201 sets of biopsies, about 17% showed abnormalities, with Giardia accounting for roughly 5% of all biopsies and mild chronic inflammation or increased immune-cell infiltration making up most of the rest.⁹ That same study noted something important: when the duodenal lining looked visually normal through the endoscope, it still harbored microscopic abnormalities roughly 18% of the time. In other words, a normal-looking duodenum does not guarantee normal tissue.

Crohn’s Disease in the Duodenum

Crohn’s disease can affect any part of the gastrointestinal tract, from the mouth to the anus, though it most commonly involves the end of the small intestine and the colon. When it does appear in the duodenum, the biopsy findings can be subtle and easy to miss if you are not looking for them. A study examining duodenal biopsies from Crohn’s patients identified a distinctive pattern: focal, patchy inflammation involving the Brunner glands, the small mucus-producing glands embedded in the duodenal wall. This particular pattern of inflammation was not found in biopsies from patients with other duodenal conditions, suggesting it could serve as a useful diagnostic clue.¹⁰

For patients already known to have Crohn’s elsewhere in their gut, a duodenal biopsy can help determine whether the disease has spread to the upper tract, which may influence treatment decisions. For patients being evaluated for the first time, Crohn’s-specific changes in a duodenal biopsy can sometimes clinch a diagnosis that has been elusive on imaging or colonoscopy alone.

Whipple’s Disease and Rare Systemic Conditions

Whipple’s disease is rare but serves as a textbook illustration of why duodenal biopsies exist. It is caused by the bacterium Tropheryma whipplei and produces a wide range of symptoms including joint pain, chronic diarrhea, weight loss, and neurological problems. The disease can be debilitating and, left untreated, fatal. Duodenal biopsy with a special stain called PAS (periodic acid-Schiff) is the most reliable way to detect it. Under the microscope, the pathologist looks for distinctive foamy immune cells packed with PAS-positive material, which represents the bacterial organisms.

A study of 191 patients with confirmed Whipple’s disease found that about 91% showed the characteristic histological changes on small bowel biopsies. In the remaining cases where the staining was not conclusive, additional molecular tests like PCR performed on the biopsy tissue brought the diagnostic yield up to 95%.¹¹ The authors concluded that despite attempts to diagnose the disease from other types of specimens, gastroscopy with duodenal biopsy remains the most reliable diagnostic tool.

A practical question that comes up in pathology labs is whether the PAS stain needs to be run on every duodenal biopsy to rule out Whipple’s, since clinicians occasionally request it even when the tissue looks unremarkable. A recent study examined this directly and found that biopsies lacking the tell-tale foamy immune cells on standard staining were never PAS-positive. When foamy cells were present and PAS staining was positive, roughly 9 out of 13 cases were ultimately confirmed as Whipple’s disease.¹² The takeaway: the special stain adds value when there is a reason to suspect the disease, but ordering it routinely on biopsies that look normal is unlikely to turn up a surprise diagnosis.

Tumors and Polyps

Though less common than celiac workups, duodenal biopsies also play a role in evaluating growths found during endoscopy. The duodenum can develop adenomas (benign growths that occasionally become cancerous) and neuroendocrine tumors, among other lesions. The problem is that these can look deceptively similar through the endoscope’s camera. A case report highlighted this issue by describing a neuroendocrine tumor that was initially mistaken for a simple adenoma and nearly removed with a technique suited only for benign polyps. Only the pathology result from the biopsy revealed the true nature of the growth, which required a completely different management approach. The lesson is that visual appearance alone is not enough to determine what a duodenal growth is, and biopsy is essential before deciding how to treat it.

Safety and Risks

Duodenal biopsies are generally very safe. Most people experience nothing more than mild bloating or a sore throat from the endoscope after the procedure. Serious complications are rare. The one that gets the most attention in the medical literature is duodenal hematoma, a collection of blood within the wall of the duodenum. It occurs mainly in children and in adults with impaired blood clotting, and presents with signs of intestinal obstruction such as pain and vomiting, sometimes accompanied by pancreatitis if the swelling presses on the bile duct.¹³ A review of reported cases confirmed this pattern: duodenal hematoma occurs predominantly in children and typically causes abdominal pain, vomiting, and pancreatitis.¹⁴

A large pediatric study specifically assessed the risk of taking extra biopsies during endoscopy and found no increased rate of complications. Children who had additional research biopsies taken during a routine procedure had a lower rate of adverse events (about 1.4% within 48 hours) than children who only had standard clinical biopsies (about 1.9%), and there was no significant link between the total number of duodenal biopsies taken and the chance of a problem.¹⁵

If you are on blood thinners or antiplatelet medications, your doctor will give you specific instructions before the procedure. Routine duodenal biopsy is considered a low-risk procedure from a bleeding standpoint, and for low-risk endoscopic procedures, guidelines generally allow patients to continue most antiplatelet and anticoagulant medications, sometimes with minor adjustments like skipping a morning dose.

Artificial Intelligence in Biopsy Interpretation

Reading duodenal biopsies requires skill and experience, and even among expert pathologists there is some degree of disagreement on borderline cases. This has made biopsy interpretation a natural target for machine-learning tools. A study published in NEJM AI tested a machine-learning model against four experienced pathologists and found that the model’s agreement with each pathologist was essentially identical to the agreement the pathologists had with each other.¹⁶ In practical terms, the algorithm was no more likely to disagree with a human expert than the experts were to disagree with one another.

Another model, tested on over 2,400 whole-slide images, was 97% accurate at distinguishing celiac disease from normal tissue and could process a slide in about a quarter of a second.¹⁷ When the model was asked to classify biopsies into five finer categories (the different Marsh stages plus normal), accuracy dropped to about 74%, which reflects the same challenge human pathologists face: the boundaries between adjacent stages of damage are genuinely ambiguous. These tools are not replacing pathologists, but they could eventually serve as a second opinion or screening step, flagging slides that need closer attention and speeding up turnaround in high-volume labs.

Capsule Endoscopy as a Less Invasive Option

For patients who cannot or prefer not to undergo a standard endoscopy, wireless capsule endoscopy offers a partial alternative. You swallow a small camera the size of a large vitamin pill, and it takes thousands of images as it travels through your digestive tract. A study comparing capsule endoscopy to standard biopsy in patients with positive celiac antibodies found that the capsule detected villous atrophy with 85% sensitivity and 100% specificity.¹⁸ That means it caught most cases but missed about 15% that the biopsy picked up, likely those with milder or patchier damage. And the capsule cannot take tissue samples, so even when it spots something abnormal, a conventional endoscopy with biopsy may still follow. For now, capsule endoscopy is better suited as a complementary tool or a screening method than a full replacement for biopsy, especially in cases where precise Marsh staging is needed to guide treatment decisions.