Lower GI Bleeding: Diverticula, Angiodysplasia, and How Doctors Diagnose It

By Joe Barnett On 30 Nov, 2025 Comments (11)

When you see bright red blood in your stool, it’s terrifying. You might think it’s just hemorrhoids. But if you’re over 60 and the bleeding is sudden, heavy, and painless, it could be something more serious-like diverticula or angiodysplasia. These are two of the most common causes of lower gastrointestinal (GI) bleeding, and knowing the difference can save your life.

What Is Lower GI Bleeding?

Lower GI bleeding means blood is coming from somewhere in your colon, rectum, or anus-anywhere past the ligament of Treitz, which is deep inside your abdomen. It usually shows up as bright red or maroon blood in your stool, called hematochezia. Sometimes, it’s just a streak on the toilet paper. Other times, it’s a full-blown gush that turns the toilet water red.

About 20 to 33% of all GI bleeds happen in the lower tract. Most patients are over 60. In the U.S., roughly 20 to 27 people out of every 100,000 get it each year. The good news? Most cases stop on their own. The bad news? If it doesn’t, and you don’t get checked quickly, you could end up in the hospital-or worse.

Diverticula: The Silent Bleeder

Diverticula are small, balloon-like pouches that stick out from the wall of your colon. They’re super common-about half of all people over 60 have them. Most never cause problems. But in about 1 in 4 of those with diverticula, one of these pouches can start bleeding.

Here’s how it happens: Blood vessels run close to the surface of the colon to feed the lining. When a diverticulum forms, it pushes these vessels outward. Over time, the vessel gets stretched thin and can rupture. There’s no inflammation, no pain, no warning. Just-bleeding.

It’s often massive. Patients describe it as a sudden gush, sometimes enough to make them faint. But because there’s no cramping or fever, many people ignore it at first. That’s dangerous. Up to 50% of hospitalizations for lower GI bleeding are due to diverticula.

The good part? About 80% of these bleeds stop on their own within 24 to 48 hours. But if it keeps going, you need help fast. Doctors will check your blood pressure, heart rate, and hemoglobin. If your hemoglobin is below 10 g/dL, you’re likely losing too much blood and may need a transfusion.

Angiodysplasia: The Slow Leak

If diverticula are the loud, sudden bleeders, angiodysplasia is the quiet one. It’s also called vascular ectasia or arteriovenous malformation (AVM). Instead of pouches, you’ve got twisted, fragile blood vessels in the colon wall-usually on the right side, near the cecum.

These vessels form because of aging. As you get older, the normal movement of your colon puts pressure on small arteries and veins. Over time, they stretch, thin out, and connect abnormally. Think of it like a garden hose that’s been kinked for years-eventually, it weakens and starts to leak.

Unlike diverticula, angiodysplasia rarely causes big, dramatic bleeds. Instead, it drips slowly. You might not even notice blood in your stool. But over weeks or months, you start feeling tired. Your skin gets pale. You get short of breath climbing stairs. That’s iron deficiency anemia from chronic blood loss.

About 3 to 6% of all lower GI bleeds come from angiodysplasia. But in people over 70, it’s the second most common cause after diverticula. And here’s the twist: if you have aortic stenosis (a narrowed heart valve), your risk goes up. The turbulent blood flow destroys a clotting protein called von Willebrand factor, making you bleed easier.

Endoscopic view of bleeding angiodysplasia vessel with plasma sparks and metallic clips in colon.

How Do Doctors Find the Source?

The first thing any ER doctor does when you show up with GI bleeding is stabilize you. They’ll give you IV fluids. They’ll check your vitals. If you’re pale, dizzy, or your heart is racing, they’ll order blood tests and prepare for a transfusion.

Then comes the key test: colonoscopy. It’s the gold standard. Done within 24 hours of admission, it finds the source in over 80% of cases and can even treat it at the same time. Studies show patients who get colonoscopy within a day have 26% lower death rates than those who wait.

But here’s the catch: if you’re bleeding heavily, your colon is full of blood. That makes it hard to see. Doctors use a trick-they give you IV fluids and a drug called erythromycin. It speeds up gut movement, helping clear the blood so the camera can get a clear view.

If colonoscopy doesn’t find anything, you’ve got what’s called “obscure” GI bleeding. That’s when the bleed is coming from deeper in the small intestine. That’s where capsule endoscopy comes in. You swallow a pill-sized camera. It takes pictures as it travels through your gut. It finds the cause in about 62% of these cases.

But there’s a risk. If you have a hidden narrowing in your intestine, the capsule can get stuck. That’s why some doctors wait until after a CT scan or device-assisted enteroscopy (a longer, more precise scope) if they suspect a stricture.

CT angiography is another powerful tool. It can spot active bleeding as slow as 0.5 mL per minute. That’s useful if you’re too unstable for colonoscopy or if the bleed is intermittent. It’s fast, non-invasive, and highly accurate-85% sensitivity.

Treatment: What Happens Next?

For diverticula bleeding, most cases don’t need surgery. If you’re stable, doctors will monitor you. If the bleeding continues, they’ll go back in with a colonoscope. They’ll inject epinephrine to shrink the blood vessels and use heat or clips to seal the spot. Success rate? 85 to 90%. But here’s the catch: 20 to 30% of people bleed again within a year.

Angiodysplasia is trickier. The go-to treatment is argon plasma coagulation (APC). It’s like using a controlled electric spark to burn the abnormal vessels shut. It works immediately in 80 to 90% of cases. But because the vessels keep forming over time, 20 to 40% of patients bleed again within a year or two.

For recurrent angiodysplasia, doctors have two medical options. One is thalidomide-yes, the same drug once used for morning sickness. Taken daily at 100 mg, it reduces bleeding by 70% in clinical trials. The other is octreotide, a hormone injection given three times a day. It helps constrict blood vessels and cuts bleeding by about 60%.

Surgery is a last resort. If the bleeding keeps coming from the same spot-like the cecum-doctors may remove that section of the colon. Right hemicolectomy is common for angiodysplasia. For diverticula, they’ll remove only the affected segment.

What’s New in 2025?

Technology is changing how we spot and treat these bleeds. AI-powered colonoscopes now flag tiny vascular lesions that human eyes might miss. One 2022 study showed a 35% increase in angiodysplasia detection using AI.

New endoscopic clips are also making a difference. A 2023 European trial found a new type of clip achieved 92% hemostasis in diverticular bleeding-better than heat or injections.

And there’s hope on the horizon. The NIH is running a phase III trial (NCT04567891) comparing thalidomide to placebo for recurrent angiodysplasia. Results are expected in late 2024. If it works, this could become standard care.

Split scene: healthy diet on one side, capsule endoscope traveling through intestines with AI-detected lesions.

What’s the Long-Term Outlook?

The good news? Most people survive. Five-year survival rates are 78% for diverticula and 82% for angiodysplasia. But survival isn’t about the bleed-it’s about your other health problems. Heart disease, kidney disease, diabetes-they’re what really affect your outcome.

The real challenge is recurrence. With diverticula, you might have one big scare and never bleed again. With angiodysplasia, you might need repeated hospital visits for years. Patients on support forums say it takes an average of 18 months to get diagnosed-many have had three or more negative colonoscopies before finding the culprit.

That’s why follow-up matters. If you’ve had one bleed, your doctor should monitor your iron levels. They might recommend repeat colonoscopies or even a capsule endoscopy if you’re still anemic.

When to Worry

Not every spot of blood is an emergency. But if you’re over 60 and you see:

Bright red blood in large amounts
Blood with no pain or itching
Signs of anemia-fatigue, dizziness, shortness of breath
History of heart valve disease or high blood pressure

-don’t wait. Go to the ER or call your doctor right away.

What You Can Do

You can’t prevent diverticula. But you can reduce your risk of bleeding:

Keep your bowel movements regular. Eat fiber-oats, beans, vegetables.
Stay hydrated. Dehydration makes stools harder and increases pressure in the colon.
Avoid NSAIDs like ibuprofen or naproxen. They can irritate the gut lining.
Manage your blood pressure and heart health. These affect blood vessel strength.

For angiodysplasia, there’s no prevention. But if you’re on blood thinners, talk to your doctor. Sometimes adjusting your medication can help.

Can diverticula bleeding be prevented?

You can’t prevent diverticula from forming, but you can lower your risk of bleeding by eating a high-fiber diet, staying hydrated, and avoiding NSAIDs. Regular colonoscopies after age 50 help catch problems early.

Is angiodysplasia cancer?

No, angiodysplasia is not cancer. It’s a vascular abnormality-fragile blood vessels in the colon wall. But because it can cause chronic bleeding and anemia, it’s often mistaken for colorectal cancer. A biopsy during colonoscopy can confirm it’s not malignant.

Why does angiodysplasia happen more in older adults?

As we age, the walls of our blood vessels weaken. Constant movement in the colon puts pressure on small arteries and veins, causing them to stretch and form abnormal connections. Over 80% of cases occur in people over 65, with an average age of 72 at diagnosis.

Can a colonoscopy miss angiodysplasia?

Yes. Angiodysplasia lesions are small and can be hidden by blood or mucus. If bleeding is intermittent, the lesion may not be active during the exam. That’s why some patients need repeat colonoscopies or capsule endoscopy if symptoms persist.

Is thalidomide safe for treating angiodysplasia?

Thalidomide is used off-label for recurrent angiodysplasia and has shown good results in clinical trials, reducing bleeding by 70%. It’s taken daily at 100 mg. Side effects include drowsiness, nerve damage, and birth defects-so it’s only used in older adults who aren’t pregnant and under close supervision.

How long does recovery take after GI bleeding?

Recovery depends on the cause and how much blood you lost. Most people feel better within a week after a one-time bleed. But if you have chronic anemia from angiodysplasia, it can take months to rebuild iron stores with supplements or transfusions. Follow-up blood tests are essential.