Small intestine bleeding most often comes from abnormal blood vessels, ulcers, or tumors within the roughly 20 feet of gut that sits between the stomach and colon. In patients over 65, vascular abnormalities account for more than half of all cases, followed by ulcers (about 13%) and tumors (about 12%). Because the small bowel is harder to reach with standard scopes than the stomach or colon, bleeding from this area has historically been difficult to pin down, and it can go undiagnosed for months.
Abnormal Blood Vessels
The single most common cause of small intestine bleeding in people over 50 is angiodysplasia: clusters of fragile, abnormally widened blood vessels in the intestinal wall. These vessels have thin walls with little or no muscle support, which makes them prone to leaking. The working theory is that as people age, normal contractions of the intestinal wall repeatedly compress the small veins running through it. Over years, that chronic compression dilates the veins, weakens nearby capillaries, and eventually creates tiny shortcuts between arteries and veins that bleed easily.
Oxygen deprivation also plays a role. When tissue in the gut wall becomes even mildly oxygen-starved, the body ramps up production of growth signals that stimulate new blood vessel formation. Those new vessels tend to be structurally weak. The combination of age-related wear and this compensatory vessel growth is why angiodysplasia is overwhelmingly a condition of older adults.
A related vascular cause is Heyde’s syndrome, seen in people with a narrowed aortic valve. The high-pressure jet of blood through the tight valve physically shreds a clotting protein (von Willebrand factor) that platelets need to seal damaged vessels. This creates a double problem: fragile intestinal blood vessels that are already prone to bleeding, paired with a clotting system that can’t stop them.
Dieulafoy Lesions
Dieulafoy lesions are unusually large arteries that sit just beneath the intestinal lining instead of deeper in the wall where they belong. They account for up to 2% of all gastrointestinal bleeding, and roughly 95% occur in the stomach. When they do appear in the small bowel, they’re notoriously hard to find. Even angiography, which maps blood vessels using contrast dye, often misses them. In reported cases, these lesions were only identified by directly visualizing the intestinal lining with specialized small-bowel endoscopy. Despite being rare, they can cause severe, life-threatening hemorrhage.
NSAIDs and Medication Damage
Non-steroidal anti-inflammatory drugs like ibuprofen and naproxen are well known for causing stomach ulcers, but they also damage the small intestine through a different mechanism. When the liver processes these drugs, it packages them into bile, which then gets dumped into the small bowel. Bacteria in the lower small intestine break down that packaging and release the active drug directly onto the intestinal lining.
Once the drug contacts the cells lining the intestine, it triggers a stress response inside those cells that can kill them. This creates small erosions and ulcers. With long-term use, repeated cycles of injury and scarring can produce ring-like strictures, sometimes called diaphragm disease, that narrow the intestinal passage. These ulcers and erosions bleed, often slowly enough that the person doesn’t notice visible blood in their stool but develops iron-deficiency anemia over weeks or months.
Blood thinners and antiplatelet medications don’t cause ulcers on their own, but they make existing lesions bleed more freely and for longer. People taking a combination of blood thinners and NSAIDs face a compounded risk.
Crohn’s Disease and Inflammatory Conditions
Crohn’s disease can affect any part of the digestive tract but has a strong preference for the last section of the small intestine (the ileum). The hallmark is deep ulceration that extends through the intestinal wall, which can erode into blood vessels. Unlike the shallow surface damage caused by NSAIDs, Crohn’s ulcers are driven by an overactive immune response and tend to be patchy, with stretches of healthy tissue between inflamed segments.
Other inflammatory conditions that can ulcerate the small bowel include celiac disease (particularly when it goes undiagnosed or untreated for years), vasculitis (inflammation of blood vessel walls), and radiation enteritis in people who’ve had abdominal radiation therapy. Each of these damages the intestinal lining through a different pathway, but the end result is the same: exposed tissue that bleeds.
Tumors and Growths
Small bowel tumors are relatively uncommon compared to stomach or colon cancers, but they cause roughly 12% of small intestine bleeding in older adults. The types that bleed most often include gastrointestinal stromal tumors (GISTs), which grow from the muscle layer of the intestinal wall and can outgrow their own blood supply, creating a crater on the surface that bleeds into the gut. Neuroendocrine tumors, adenocarcinomas, and lymphomas also occur in the small bowel. Even benign growths like polyps and lipomas can bleed if they’re large enough for the intestinal contents to repeatedly rub against them.
Because small bowel tumors grow in an area that’s difficult to image with standard tests, bleeding is sometimes the first sign that a tumor exists at all.
Meckel’s Diverticulum
This is a small pouch in the wall of the lower small intestine that’s present from birth, a leftover from fetal development. About 2% of the population has one, and most never know it. The pouch becomes a problem when it contains tissue that mimics the stomach lining. That misplaced tissue produces acid in a location that isn’t designed to handle it, and the acid eats into the surrounding intestinal wall, creating ulcers that bleed. Meckel’s diverticulum is the most common congenital cause of small bowel bleeding and is a particularly important consideration in children and young adults with unexplained intestinal hemorrhage.
How Small Bowel Bleeding Shows Up
The appearance of blood in your stool depends on how fast the bleeding is and where in the small intestine it originates. Slow or moderate bleeding from the small bowel typically produces melena: black, tarry, sticky stools with a distinctive strong odor. The blood turns black because digestive enzymes and bacteria break it down during the hours it takes to travel through the rest of the intestine.
Rapid small bowel bleeding, particularly from an arterial source like a Dieulafoy lesion or a large ulcer, can move through the gut fast enough to appear as bright or dark red blood in the stool. This presentation can mimic colon bleeding, which is one reason small bowel sources are sometimes missed on initial evaluation. In cases of very slow, chronic bleeding, there may be no visible change in stool color at all. Instead, the first clue is often unexplained iron-deficiency anemia, fatigue, or a positive fecal occult blood test.
How the Bleeding Source Is Found
The small intestine sits in a diagnostic blind spot. Standard upper endoscopy reaches only the first short segment, and colonoscopy can peek into the very last portion. When bleeding can’t be explained by either of those exams, the American College of Gastroenterology recommends video capsule endoscopy as the first-line test for evaluating the small bowel. This involves swallowing a pill-sized camera that takes thousands of images as it travels through the entire intestine.
Timing matters. Capsule endoscopy performed within 48 to 72 hours of an active bleeding episode has the highest chance of finding the source. When the test is done within two weeks of bleeding, detection rates reach about 91%, compared to just 34% when it’s delayed longer. Active or recent bleeding, a hemoglobin level below 10 g/dL, and a history of more than one bleeding episode all increase the likelihood of a positive finding.
If the capsule identifies a lesion, or if bleeding is too heavy to wait for capsule results, deep enteroscopy (a long, flexible scope that can reach further into the small bowel) allows both diagnosis and treatment in the same session. Treatment options during enteroscopy include sealing bleeding vessels with heat, placing small clips on them, or injecting medication to constrict the blood supply around the site.