Biopsies are not taken during every colonoscopy. Whether your doctor removes tissue samples depends on what they find (or suspect) during the exam and why the procedure was ordered in the first place. In one large review, biopsies were taken in about 35% of all colonoscopies, meaning roughly two-thirds of patients had none at all.1PubMed Central. Colon biopsies: benefit or burden? The decision is driven by a few specific clinical scenarios, and understanding those scenarios can help you make sense of what happened during your procedure or what to expect if you have one coming up.
When Biopsies Are Routine
The most common reason for a biopsy during a colonoscopy is the discovery of a polyp. Polyps are small growths on the lining of the colon, and because some of them can eventually become cancerous, the standard practice is to remove them on the spot. This is technically a polypectomy rather than a simple biopsy, but from your perspective as a patient, it feels similar: tissue is removed and sent to a lab. If the polyp is small enough, the doctor uses a tiny wire loop or forceps passed through the scope. Larger polyps may require more involved techniques. The key point is that if a polyp is found, it almost always comes out. A forceps biopsy alone, where only a small pinch of the polyp is sampled, carries the risk of missing abnormal cells because only a fraction of the growth is examined.2European Journal of Gastroenterology & Hepatology. Polyps in the gastrointestinal tract: discrepancy between endoscopic forceps biopsies and resected specimens For that reason, complete removal is preferred whenever possible.
The second common scenario is a colonoscopy done to investigate chronic diarrhea. Here, biopsies are often taken even when the colon looks perfectly normal through the camera. That might seem counterintuitive, but conditions like microscopic colitis produce inflammation that is invisible to the naked eye. A systematic review pooling data from multiple studies found that among patients with chronic diarrhea and a normal-appearing colon, about 15% turned out to have microscopic colitis on biopsy.3iGIE. Diagnostic yield of random colon biopsy sampling in patients with chronic diarrhea and normal colonoscopy: a systematic review and meta-analysis That is a substantial number of people who would have gone undiagnosed if biopsies had been skipped. For this reason, guidelines generally recommend random biopsies from several spots along the colon when the procedure is done to evaluate unexplained diarrhea.4PubMed Central. The role of mucosal biopsy in the diagnosis of chronic diarrhea: value of multiple biopsies when colonoscopic finding is normal or nonspecific
A third scenario involves people who have inflammatory bowel disease. If you have ulcerative colitis or Crohn’s disease, surveillance colonoscopies are a regular part of your care, and biopsies are almost always taken. The goal is to detect dysplasia, which is a precancerous change in the cells lining the colon. These changes can be invisible during the procedure but show up under a microscope, so random biopsies from multiple sites are standard practice during IBD surveillance.5PubMed Central. Management of Dysplasia in Inflammatory Bowel Disease Biopsies also help gastroenterologists assess whether the inflammation from IBD has actually healed at the tissue level, even if the surface looks normal on camera.6PubMed Central. Assessment of mucosal healing in inflammatory bowel disease: review
When Biopsies Are Usually Skipped
If you are having a routine screening colonoscopy and the doctor finds nothing abnormal, there is generally no reason to take biopsies. The scope gives a detailed, real-time view of the colon lining, and in a healthy-looking colon with no polyps, no inflammation, and no suspicious areas, taking random tissue samples from a screening patient adds time and cost without a clear payoff. One study that looked at colonoscopies with a completely normal appearance found that only about 7.5% of random biopsies from those normal-looking colons turned up anything on pathology.7PubMed Central. Colon biopsies: benefit or burden? – Section: Results That is not zero, but the yield is low enough that random sampling in routine screenings is not considered standard.
The distinction matters: the reason you are having the colonoscopy shapes whether biopsies are warranted. A screening colonoscopy in a person with no symptoms and no personal history of IBD or colon cancer is a fundamentally different clinical situation from a diagnostic colonoscopy in someone with months of watery diarrhea. The same clean-looking colon can mean “no biopsy needed” in the first patient and “definitely biopsy this” in the second.
The Pediatric Exception
For children, the question of routine biopsies is handled a bit differently. A study examining the value of biopsying normal-looking colon tissue in pediatric patients concluded that biopsies may not need to be routinely obtained from all pediatric colonoscopies, particularly in children whose main complaint is abdominal pain.8PubMed. The Value of Obtaining Colonic Mucosal Biopsies of Grossly Normal Tissue in Pediatric Patients Children undergoing colonoscopy for suspected IBD or bloody stools may still warrant biopsies, but for the common scenario of a child with belly pain and a normal-appearing colon, the evidence suggests that the tissue samples rarely change the diagnosis or the treatment plan. This is an area where clinical judgment varies from one pediatric gastroenterologist to another.
What Happens If a Polyp Is Found
Finding a polyp changes the equation immediately. The doctor will almost certainly remove it during the same procedure. For very small polyps, a cold snare technique is common: a thin wire loop is passed around the polyp and cinched closed, slicing the growth off without using electrical current. The tissue is then retrieved through the scope and sent to pathology. Forceps biopsies, where a small clamp takes a pinch of tissue, are sometimes used on tiny bumps but are less reliable for determining exactly what a polyp contains. When only a small portion is sampled, abnormal areas within the polyp can be missed entirely, which is why complete removal is the goal whenever the polyp’s size and location allow it.2European Journal of Gastroenterology & Hepatology. Polyps in the gastrointestinal tract: discrepancy between endoscopic forceps biopsies and resected specimens
One interesting wrinkle involves how polyps are measured after removal. A prospective study found that polyps shrink by roughly 26% when they are placed in formalin, the preservative used for lab analysis. That shrinkage caused about a third of polyps that measured 10 millimeters or more before fixation to be classified as under 10 millimeters afterward.9BMJ Journals. Accuracy of measuring colorectal polyp size in pathology: a prospective study This matters because polyp size influences follow-up recommendations: a polyp that gets reclassified as smaller than it actually was could lead to a longer interval before the next colonoscopy, when a shorter one would have been more appropriate. Researchers have found that measuring polyps during the procedure itself, using laser-based tools on the endoscope, is more accurate than relying on the lab measurement after the tissue has been preserved.
Bleeding Risk and Blood Thinners
One of the practical concerns patients have about biopsies is whether they increase the risk of bleeding. For standard pinch biopsies of flat tissue, the risk is very low. The situation gets more nuanced when polyps are removed, because polypectomy involves cutting or snaring a growth that has its own blood supply.
A study of over 1,600 patients who had polypectomies found an overall bleeding rate of about 2.2%. The strongest risk factor was warfarin use, which increased bleeding risk substantially compared to other factors like polyp size or location.10PubMed. Risk of colonoscopic polypectomy bleeding with anticoagulants and antiplatelet agents: analysis of 1657 cases Aspirin and common anti-inflammatory drugs, on the other hand, did not significantly raise the risk of major bleeding after polypectomy in that analysis. A separate study found that while minor, self-limited bleeding was more common in patients taking NSAIDs, the risk of serious bleeding requiring treatment was under 1% regardless of whether patients were on these medications.11PubMed. Risk of bleeding after endoscopic biopsy or polypectomy in patients taking aspirin or other NSAIDS
If you take a blood thinner like warfarin or a newer anticoagulant, your doctor will weigh the risk of post-polypectomy bleeding against the risk of a blood clot if the medication is temporarily stopped. This balancing act is one of the reasons your pre-procedure instructions may ask about every medication you take, including over-the-counter supplements and herbal products that can affect clotting.
The Limits of Biopsy Accuracy
Biopsies are extremely useful, but they are not infallible. Even when tissue is taken from a suspicious area, there is a small chance of a missed diagnosis. The sensitivity of tissue biopsy for detecting colorectal cancer during colonoscopy has been reported at around 87%, meaning a small number of cancers go undetected on the initial sample. The overall rate of missed colorectal cancers across screening colonoscopies is estimated at roughly 0.5 to 3.5 per 1,000 procedures, a figure that includes not just biopsy misses but also lesions that were not seen at all or incompletely removed.12PubMed Central. Failure of 3 different methods and biopsy sites to diagnose a patient with invasive colorectal cancer
Efforts to improve accuracy are ongoing. One approach involves using cold snare biopsy instead of conventional forceps for suspected cancerous lesions. A study comparing the two techniques found that cold snare biopsies achieved 100% diagnostic consistency with the final surgical specimen, compared to about 87% for forceps biopsies.13PubMed. Cold Snare Biopsy to Increase Diagnostic Accuracy in Patients With Suspected Colorectal Cancer Under Colonoscopy The cold snare captures a larger and deeper tissue sample, which gives the pathologist more material to work with.
Ischemic Colitis and Other Less Common Reasons
Beyond polyps, chronic diarrhea, and IBD surveillance, biopsies are sometimes taken to diagnose conditions that produce visible changes in the colon wall. Ischemic colitis, where part of the colon loses its blood supply temporarily, is one such condition. Colonoscopy combined with biopsy is considered the standard diagnostic approach for ischemic colitis, because the tissue samples help distinguish it from other causes of inflammation like infection or IBD.14PubMed Central. Diagnostic methods and drug therapies in patients with ischemic colitis If the doctor sees patchy redness, swelling, or ulcers in a pattern that suggests reduced blood flow, biopsies from the affected area confirm the diagnosis and help guide treatment.
Infections, graft-versus-host disease after a bone marrow transplant, and certain medication-related injuries to the colon are other situations where biopsies of abnormal-looking tissue clinch a diagnosis that would otherwise remain uncertain. In each of these cases, the decision to biopsy is driven by what the gastroenterologist sees through the scope or by the clinical context rather than by a blanket protocol applied to every patient.
How Biopsy Results Shape Your Follow-Up Schedule
The results of a biopsy or polypectomy directly determine when you will need your next colonoscopy. If no polyps are found and no biopsies are taken during a routine screening, the standard recommendation is to return in ten years for average-risk adults. If polyps are found and removed, the timeline shortens based on the number of polyps, their size, and what the pathology report says about them. Higher-risk findings like advanced adenomas or large polyps typically move the next colonoscopy to three years. Shorter intervals may be recommended when adenoma findings are concerning.15PubMed. Guidelines for colonoscopy surveillance after cancer resection: a consensus update by the American Cancer Society and US Multi-Society Task Force on Colorectal Cancer
For patients with IBD, the stakes of biopsy results are particularly high. A long-term analysis of colonoscopic surveillance in ulcerative colitis found that when surgery was ultimately performed because of high-grade dysplasia detected on biopsy, nearly half of the surgical specimens turned out to contain actual cancer. Even among patients who had surgery for the less concerning low-grade dysplasia, about a quarter had cancer in the removed colon.16PubMed Central. Forty-Year Analysis of Colonoscopic Surveillance Program for Neoplasia in Ulcerative Colitis: An Updated Overview These numbers underscore why regular surveillance biopsies in IBD patients are taken so seriously, and why a finding of dysplasia typically leads to prompt referral to a specialist.
Could AI Eventually Reduce the Need for Biopsies?
An emerging area of research involves using artificial intelligence to analyze the appearance of polyps and tissue during the colonoscopy itself, potentially predicting what the pathology report would say without removing tissue at all. Computer-aided diagnosis systems are being trained to classify polyps in real time, distinguishing harmless hyperplastic polyps from precancerous adenomas based on their surface patterns and color under enhanced imaging.17PubMed Central. Artificial Intelligence–Assisted Optical Diagnosis: A Comprehensive Review of Its Role in Leave-In-Situ and Resect-and-Discard Strategies in Colonoscopy
If these systems prove reliable enough, two strategies could become widespread. The first, sometimes called “resect and discard,” would allow doctors to remove a tiny polyp and throw it away rather than sending it to the lab, saving time and money when the AI confidently predicts the polyp is benign. The second, “leave in situ,” would mean that very small, clearly harmless-looking polyps are simply left in place and monitored. Neither approach has fully replaced traditional biopsy-and-pathology workflows yet, and the technology still needs to meet high accuracy thresholds before it is trusted with the decision to skip a lab analysis. But the trajectory suggests that in the future, fewer of those tiny tissue pinches may be necessary.
The Evolving Debate Over Random Biopsies
Even within the well-established indication of chronic diarrhea, there is active debate about how many biopsies are truly needed and from which locations. A traditional recommendation for diagnosing microscopic colitis has been to take bilateral biopsies from multiple segments of the colon, sometimes resulting in a dozen or more tissue samples from a single procedure. Recent work has challenged this, presenting data suggesting that fewer, more targeted biopsies may be sufficient to make the diagnosis without sacrificing accuracy.18PubMed Central. Letter to the Editor: Less can be more, rethinking colonic biopsy strategies for microscopic colitis in the era of green endoscopy This fits into a broader push in gastroenterology toward “green endoscopy,” which aims to reduce waste, processing time, and resource use without compromising patient care. The idea is that taking fewer samples, if those samples are from the right locations, can be just as diagnostic while generating less pathology lab work and less single-use supply consumption. How widely this will reshape practice remains to be seen, but the conversation reflects a field that is constantly re-evaluating when biopsies add value and when they add only cost.