What Is Lower GI Bleeding?
Lower gastrointestinal (GI) bleeding means blood is coming from somewhere in your colon, rectum, or anus - anywhere past the ligament of Treitz. It usually shows up as bright red or maroon blood in your stool, sometimes in large amounts. You might not feel pain, which makes it confusing. Some people think it’s just hemorrhoids, but it could be something more serious like diverticula or abnormal blood vessels called angiodysplasia.
It’s not rare. About 20 to 33% of all GI bleeds happen in the lower tract, and most people who get it are over 60. The good news? Many cases stop on their own. The bad news? If it’s heavy or keeps coming back, you need to act fast. Left untreated, chronic bleeding can lead to severe anemia, fatigue, and even hospitalization.
Diverticula: The Most Common Cause
Diverticula are small pouches that stick out from the wall of your colon. They form because of weak spots in the muscle, often due to years of low-fiber diets and pressure inside the bowel. About 30 to 50% of people over 60 have them - and about one in five of those will bleed at some point.
Here’s what makes diverticular bleeding different: it’s sudden, painless, and often massive. You might go from normal bowel movements to seeing a cupful of bright red blood in the toilet. No cramps, no fever - just blood. That’s because the bleeding comes from a small artery that runs close to the surface of the diverticulum. When it erodes, it bleeds hard - but often stops by itself.
Studies show about 80% of these bleeds stop without any treatment. But if it keeps going, doctors will use colonoscopy to find the spot and stop it with epinephrine injections or heat probes. Rebleeding happens in 20 to 30% of cases, so follow-up is key.
Angiodysplasia: The Silent Bleeder
Angiodysplasia - also called vascular ectasia or AVM - is the second most common cause of major lower GI bleeding in older adults. These aren’t tumors. They’re tangled, fragile blood vessels that form in the right side of the colon, especially near the cecum. They grow slowly over time as the colon moves, stretching small arteries and veins until they connect abnormally.
Unlike diverticula, angiodysplasia rarely causes big, dramatic bleeds. Instead, it leaks slowly. You might not even notice blood in your stool. But over weeks or months, you’ll feel tired, dizzy, or short of breath. That’s because you’re losing iron quietly. Your hemoglobin drops. You’re anemic - and you might not realize why.
It’s more common in people over 70. And if you have aortic stenosis (a narrowed heart valve), your risk goes up. The turbulent blood flow damages a clotting protein called von Willebrand factor, making you more prone to bleeding. That’s why doctors look for heart problems when someone has recurrent GI bleeds with no clear cause.
How Do Doctors Find the Source?
When you show up with GI bleeding, the first thing the team does is check your vitals. Are you pale? Is your heart racing? Is your blood pressure low? If yes, they’ll start IV fluids and maybe give you blood right away.
Then they run basic tests: a complete blood count (CBC) to see how low your hemoglobin is, clotting studies, and a type and crossmatch in case you need transfusion. If your hemoglobin is under 10 g/dL, you’re in the danger zone.
Colonoscopy is the gold standard. It’s done within 24 hours if you’re stable enough. The goal isn’t just to see the bleed - it’s to stop it. Modern colonoscopes with high-definition imaging and AI tools can spot tiny angiodysplasia lesions that older scopes missed. One 2022 study showed AI boosted detection by 35%.
But what if the colonoscopy comes back clean? That happens in up to 30% of cases. Then it gets trickier. You might need a CT angiogram - a special scan that can catch active bleeding as slow as 0.5 mL per minute. Or a capsule endoscopy: you swallow a tiny camera that takes pictures as it travels through your small intestine. It finds the cause in about 62% of these obscure cases.
But here’s the catch: capsule endoscopy can get stuck if you have a hidden narrowing in your bowel. That’s why some experts say to do device-assisted enteroscopy first - a longer, more invasive scope that can reach deeper. It finds the problem in 71% of cases but needs a specialist.
Treatment: What Works and What Doesn’t
For diverticula bleeding, if it’s not life-threatening, most doctors will watch and wait. Fluids, rest, and maybe a blood transfusion. If it keeps bleeding, endoscopic therapy works in 85 to 90% of cases. Epinephrine injections stop the flow by constricting blood vessels. Then heat or clips seal the spot. Newer clipping devices have hit 92% success in European trials.
Angiodysplasia is harder to cure. Argon plasma coagulation (APC) is the go-to. It zaps the vessels with a gas beam. It stops bleeding right away in 80 to 90% of cases. But here’s the problem: it doesn’t last. Up to 40% of patients rebleed within two years. That’s why some need repeat treatments every few months.
For those with frequent bleeds, medications can help. Thalidomide - yes, the same drug once linked to birth defects - is now used off-label at 100 mg daily. A 2019 study in Gut showed it cut transfusion needs by 70%. Octreotide, a hormone-like drug, can also reduce bleeding by tightening blood vessels. It’s given as injections under the skin, three times a day.
Surgery is a last resort. If the bleeding is stuck in one area - say, the cecum - a right hemicolectomy (removing the right side of the colon) can be curative. For diverticula, a segmental resection works if the problem is localized.
What Happens After the Bleed?
Survival rates are actually pretty good. Five-year survival for diverticular bleeding is around 78%. For angiodysplasia, it’s 82%. But that’s not because the bleeding itself is harmless. It’s because most people who get these bleeds are older and have other health problems - heart disease, kidney issues, diabetes. The bleed is often the trigger, not the main cause.
Recurrent bleeding is the real challenge. One patient survey found people with angiodysplasia wait an average of 18 months to get diagnosed. They go through three or more negative colonoscopies before someone spots the subtle lesions. That’s frustrating, expensive, and exhausting.
That’s why some hospitals now use standardized LGIB protocols. Nurses, ER docs, gastroenterologists, and radiologists all follow the same steps. It cuts delays, reduces errors, and saves lives.
What Should You Do If You See Blood in Your Stool?
Don’t ignore it. Don’t assume it’s hemorrhoids. Even if it stops, get checked. A single episode of painless, heavy bleeding could be diverticula - and while it often resolves, it signals you’re at higher risk for another one.
If you’re older, have fatigue, or are on blood thinners, be extra careful. Talk to your doctor about your meds. Blood thinners like warfarin or apixaban can make bleeding worse. Sometimes adjusting the dose helps.
And if you’ve had multiple episodes? Push for advanced imaging. Don’t accept a ‘no findings’ result if you’re still symptomatic. Ask about capsule endoscopy or CT angiography. And if you have a heart valve problem, mention it - it could be the missing link.
What’s New in 2026?
The field is moving fast. AI-assisted colonoscopy is now standard in many hospitals. It highlights suspicious vessels in real time. New endoscopic clips are stronger, easier to place, and work even in wet, bloody fields.
A major NIH trial is wrapping up right now - comparing thalidomide to placebo for recurrent angiodysplasia. Results are expected in late 2024, and if positive, this could become a first-line treatment.
There’s also growing interest in genetic markers. Some people seem genetically prone to vascular malformations. Future testing might identify those at risk before they bleed.
Bottom Line
Lower GI bleeding isn’t one thing. It’s two big players - diverticula and angiodysplasia - plus a few others. Diverticula bleed hard and fast, but often stop on their own. Angiodysplasia bleeds slow, and you might not notice until you’re anemic.
Colonoscopy is still your best friend. Do it early. Don’t delay. And if it doesn’t show anything, don’t give up. Keep pushing for answers. Your quality of life depends on it.
Most people recover well. But the key is catching it before it becomes a pattern. One bleed is scary. Three bleeds? That’s a wake-up call.
Is lower GI bleeding always serious?
Not always, but it should never be ignored. About 80% of diverticular bleeds stop on their own. But if you’re losing a lot of blood quickly, or if you’re elderly or on blood thinners, it can become life-threatening. Chronic, low-level bleeding from angiodysplasia can lead to severe anemia over time. Either way, you need medical evaluation.
Can I prevent diverticula from bleeding?
You can’t reverse diverticula once they form, but you can lower your risk of bleeding. Eat more fiber - whole grains, beans, vegetables, fruits. Stay hydrated. Avoid heavy lifting or straining during bowel movements. Some studies suggest regular aspirin use may increase bleeding risk, so talk to your doctor if you’re on daily aspirin.
Why does angiodysplasia keep coming back?
Because the abnormal blood vessels don’t disappear after treatment. Endoscopic methods like APC burn the surface, but the underlying malformed vessels remain. Over time, new ones can form, or the treated ones re-open. That’s why recurrence rates are high - up to 40% within two years. Long-term medical therapy or repeated procedures are often needed.
Can a colonoscopy miss angiodysplasia?
Yes, especially if the bleeding has stopped. Angiodysplasia lesions are small, flat, and can look like normal tissue. They’re easiest to spot when actively oozing. If you’re bleeding intermittently, a colonoscopy done between episodes might miss them. That’s why doctors sometimes repeat the scope or use capsule endoscopy if symptoms persist.
Is thalidomide safe for treating angiodysplasia?
It’s used off-label and requires careful monitoring. Thalidomide can cause nerve damage (peripheral neuropathy), drowsiness, and birth defects - so it’s not used in pregnant women or without strict controls. But for older adults with recurrent bleeding who’ve tried everything else, the benefits often outweigh the risks. Blood tests and neurological checks are done regularly.
Should I get screened for lower GI bleeding if I’m over 60?
Routine screening for LGIB isn’t recommended unless you have symptoms like blood in stool, unexplained anemia, or a history of bleeding. But colon cancer screening (like colonoscopy at age 45+) does catch diverticula and early angiodysplasia. So if you’re due for a colonoscopy, use it as an opportunity to check for these conditions too.