Lower GI Bleeding: What You Need to Know About Diverticula and Angiodysplasia

When you see bright red blood in your stool, it’s natural to panic. But not all lower GI bleeding is the same. Two of the most common causes-diverticula and angiodysplasia-look very different on the surface, even though they both lead to bleeding from the colon. One can dump a liter of blood in minutes. The other might slowly drain your iron stores over months, leaving you tired and weak without ever giving you a single bloody stool. Knowing the difference isn’t just academic-it changes how you’re treated, how long you stay in the hospital, and whether you’ll need surgery.

What Exactly Is Lower GI Bleeding?

Lower gastrointestinal bleeding means blood is coming from somewhere in your colon, rectum, or anus. It’s not the same as upper GI bleeding, which comes from the stomach or small intestine and usually turns stool black and tarry (melena). Lower GI bleeding shows up as hematochezia-bright red or maroon blood mixed in with stool or passed separately. It’s common in people over 60. About 20 to 27 out of every 100,000 adults experience it each year in the U.S., and the numbers are rising as the population ages.

Most cases stop on their own. But when they don’t, the real challenge is figuring out why. Two conditions account for nearly half of all serious cases: diverticula and angiodysplasia. These aren’t rare quirks-they’re the leading culprits behind hospital admissions for GI bleeding.

Diverticula: The Silent Burst

Diverticula are small pouches that stick out from the wall of your colon. They form where the muscle layer is weak, usually in the sigmoid colon (the lower left side). Almost half of people over 60 have them. Most never cause problems. But in about 1 in 5, a blood vessel that runs along the outside of the pouch gets torn.

This isn’t diverticulitis-there’s no infection or inflammation. It’s purely a vascular rupture. The vessel, called the vasa recta, runs right beneath the mucosa. When a diverticulum forms, the vessel gets pulled over the top of the pouch. It’s like a rubber band stretched too tight. A sudden pressure change-maybe from straining, lifting, or even just a hard bowel movement-can snap it.

The result? Massive, painless bleeding. Patients often describe it as "gushing" or "like a faucet turned on." Some lose over a liter of blood in minutes. They may feel dizzy, faint, or get chest pain from low blood pressure. But they don’t have abdominal pain. That’s a key clue: if you’re bleeding heavily and your belly feels fine, diverticula are likely the cause.

Good news: 80% of these bleeds stop without any treatment. Your body clots the vessel naturally. The rest need help-usually endoscopic therapy. Doctors use a scope to find the bleeding point, inject epinephrine to shrink the vessel, then apply heat or clips to seal it. Success rates are high-85 to 90% stop bleeding right away. But about 1 in 4 will bleed again within a year.

Angiodysplasia: The Slow Leak

Angiodysplasia is a fancy term for abnormal blood vessels in the colon. They’re not tumors. They’re not infections. They’re just stretched-out, fragile capillaries that form tiny connections between arteries and veins-like a leaky garden hose that’s been twisted too many times. These are most common in the right side of the colon, especially the cecum.

Why here? Because blood flow is higher in the right colon. As you age, the vessels lose elasticity. They dilate. Over time, they become so thin-walled that they bleed with every bowel movement. Unlike diverticula, this isn’t a sudden event. It’s a drip-feed. You might not even notice the blood. Instead, you feel tired. Your skin looks pale. Your heart races with minimal effort. Your doctor finds you’re anemic-hemoglobin below 10 g/dL-and wonders why.

Angiodysplasia is the second most common cause of major lower GI bleeding after diverticula. It’s rare under 50. After 70, it becomes much more common. Over 80% of cases occur in people over 65. The average age at diagnosis is 72.

Here’s a twist: angiodysplasia is sometimes linked to heart disease. If you have aortic stenosis-a narrowed heart valve-the turbulent blood flow can break down a clotting protein called von Willebrand factor. That makes you more likely to bleed from these fragile vessels. So if you’re an older patient with both heart valve disease and recurring anemia, your doctor should suspect angiodysplasia.

Diagnosing it is tricky. These lesions are small, flat, and often hidden under mucus. A standard colonoscopy can miss them. That’s why experts now use high-definition scopes with dye spraying or narrow-band imaging to highlight the red, spiderweb-like vessels. Even then, they’re easy to overlook.

The Workup: How Doctors Find the Source

When you arrive at the ER with GI bleeding, the first priority is stabilization. Are you dizzy? Is your heart racing? Is your blood pressure dropping? If yes, you get fluids, oxygen, and maybe a blood transfusion right away.

Then comes the workup:

1. Lab tests: CBC (to check hemoglobin), coagulation panel (to rule out clotting disorders), and type and crossmatch (in case you need blood).
2. Colonoscopy: This is the gold standard. It’s done within 24 hours if you’re stable enough. Studies show early colonoscopy cuts death risk by 26%. Even if you’re bleeding, doctors can use IV fluids and erythromycin to clear the bowel fast. No need to wait for perfect prep.
3. CT angiography: If colonoscopy doesn’t find the source, and you’re still bleeding, a CT scan with contrast can pinpoint active bleeding at rates as low as 0.5 mL per minute. It’s fast, non-invasive, and great for emergencies.
4. Capsule endoscopy or enteroscopy: If the bleeding keeps coming back and colonoscopy was clean, they’ll look higher up-into the small bowel. Capsule endoscopy (a pill-sized camera) finds the cause in 62% of cases. But it can get stuck in narrowed areas. Device-assisted enteroscopy (a longer scope with balloons) finds 71% of cases but requires more skill and time.

One big mistake? Assuming every anemic elderly patient has angiodysplasia. Many have incidental vascular changes that aren’t bleeding. A 2022 Harvard Health review warned that up to 40% of these "findings" are red herrings. Only treat if there’s clear evidence of active bleeding.

Treatment: What Works and What Doesn’t

For diverticula, the goal is to stop the current bleed and prevent recurrence. Surgery is rarely needed unless bleeding keeps coming from the same spot. For angiodysplasia, the problem is recurrence. Even after successful APC, up to 40% will bleed again within two years.

That’s where newer drugs come in. Thalidomide, once known for birth defects, has shown surprising promise. A 2019 study in Gut found that 100 mg daily reduced transfusion needs by 70% in patients with recurrent angiodysplasia. Octreotide, a hormone that narrows blood vessels, works in about 60% of cases when given as daily injections. Both are used off-label but are now part of standard protocols at major centers.

And there’s new tech. AI-assisted colonoscopy systems now flag angiodysplasia lesions in real time, boosting detection by 35%. New endoscopic clips are also proving more effective than heat for sealing diverticular bleeds-92% success in a 2023 European trial.

What Happens After the Bleed?

Your prognosis depends less on the bleeding itself and more on your other health problems. About 10-22% of people with diverticular bleeding die within 30 days-but not because of the bleed. It’s usually heart failure, kidney disease, or infection. For angiodysplasia, mortality is lower (5-10%), but quality of life suffers. Patients often endure multiple hospital stays, iron infusions, and endless colonoscopies.

One patient from the Inspire GI community said: "I had five negative colonoscopies before they finally found the lesion. I thought I was being ignored. I felt like a broken machine." That’s not uncommon. The average time from first symptom to diagnosis for angiodysplasia is 18 months.

For diverticula, most people never bleed again. But if you’ve had one episode, you’re at higher risk. Avoid heavy lifting. Stay well-hydrated. Eat fiber-not just for constipation, but to reduce pressure in the colon. No need for routine repeat colonoscopies unless you have other risk factors like polyps or family history of colon cancer.

When to Worry

Not every speck of blood means disaster. But if you’re over 60 and notice:

• Sudden, large amounts of bright red blood
• Unexplained fatigue, dizziness, or shortness of breath
• Repeated episodes of anemia without a clear cause

-get checked. Don’t wait. Don’t assume it’s hemorrhoids. Don’t brush it off as "just aging." The tools to find and fix these problems exist. And they work.

Right now, the NIH is running a phase III trial comparing thalidomide to placebo for recurrent angiodysplasia. Results are due in late 2024. That means better treatments are coming. But for now, the key is early diagnosis-and knowing when to ask for the right test.

What Comes Next?

If you’ve had one episode of lower GI bleeding, you’re now in a higher-risk group. Follow up with your gastroenterologist. Ask if you need repeat colonoscopy. If you’re anemic, get iron levels checked-not just hemoglobin. If you have heart disease, mention it. Angiodysplasia doesn’t show up on every test. But if you’ve had three negative scopes and still feel weak, push for capsule endoscopy or CT angiography.

The good news? Most people recover fully. With modern tools, we can find these hidden bleeds. We can stop them. And we’re getting better at preventing them from coming back. You don’t have to live with fatigue or fear. You just need to speak up-and get the right test at the right time.