Lower GI Bleed

With rare exceptions, there are usually no clear answers in the ER for what causes lower GI bleeding. We have tests to check hemoglobin, which measures the amount of red blood cells you have. (When you donate blood, this is usually what you’re donating. Donating plasma or platelets is less common.) We can also check clotting factors such as platelets, as well as a test called INR, which assesses how well your blood should clot. We generally perform CT scans of the abdomen as well, but we rarely find a definitive answer.

The reason is that most GI bleeds are slow. A CT scan can show evidence of internal bleeding, but this usually relates to traumatic injuries. When looking for internal bleeding from trauma, we are mainly checking the solid organs like the liver, kidneys, and spleen—that type of bleeding can be seen on CT. Injuries to large blood vessels can also be visible. For example, if someone ruptures a major blood vessel in the pelvis from a severe pelvic fracture, we can often see it. However, GI bleeding is generally caused by very small blood vessels, so it is not easily detected on a CT scan.

As an analogy: If you cut a garden hose with a utility knife, that’s pretty obvious. This is similar to a major blood vessel injury or significant damage to a solid organ—the CT scan would likely pick it up. But if you take a very small nail and punch a tiny hole in the garden hose, that’s much harder to find. If it’s not bleeding briskly, the CT won’t detect it. And that’s generally how lower GI bleeds cause rectal bleeding.

Many patients with lower GI bleeds are on blood thinners. Just as they are more likely to bruise from minor trauma, they are also more prone to bleeding from very small vessels.

A few external causes around the rectum can lead to GI bleeding, most notably anal fissures and external hemorrhoids. These are usually found on a physical exam. An anal fissure is essentially a tear in the rectal mucosa, most often caused by a very large, firm bowel movement. Despite being a break in the skin that’s constantly exposed to bacteria, anal fissures almost never get infected due to their location. External hemorrhoids can also bleed and are often quite painful.

Internal hemorrhoids, on the other hand, are generally considered painless (especially compared to external ones), but they can cause significant bleeding. They are not as easily detected on physical exams. A digital rectal exam might pick them up, but it’s hard to be certain that internal hemorrhoids are the source of bleeding when you can’t actually see them.

Polyps, which are commonly found on colonoscopy, typically do not bleed. However, after a colonoscopy in which polyps are removed or biopsies are taken, some bleeding can occur. Colon cancer and inflammatory bowel disease can also cause lower GI bleeding, but these are relatively uncommon. Most patients with these conditions already have a known history before coming to the ER. Occasionally, a new diagnosis of colon cancer is made in the ER, and inflammatory bowel disease is diagnosed even less frequently. Some CT findings suggestive of inflammatory bowel disease can also appear in people who simply have mild irritation or inflammation of the colon. Seeing these changes once does not confirm a diagnosis of inflammatory bowel disease.

In the last month, I’ve seen two patients in the ER with lower GI bleeding. One was in his 30s and relatively healthy. We did the usual workup as described above: hemoglobin was normal, the CT scan showed no acute findings, and there was no recurrence of bleeding during several hours of observation in the ER. He was discharged with a plan to follow up in the GI clinic.

The other patient was an elderly woman. The most recent hemoglobin in her chart was from over a year earlier. On this visit, her hemoglobin was 9. Transfusions don’t usually happen above 7 (sometimes around 8), but with such a significant drop, there was no way to know whether this was an acute change, which is obviously more concerning, or the result of slow blood loss and gradually declining hemoglobin over the past year—a common occurrence in patients with multiple chronic diseases. She was admitted to the hospital for further evaluation. Logistically, this means GI would likely see her during daytime hours, discuss a possible colonoscopy (which may or may not happen during the admission), or schedule it as an outpatient procedure if her hemoglobin remains stable and she shows no worsening vital signs or ongoing bleeding.

It’s worth mentioning that a colonoscopy requires bowel prep. This means the patient must have virtually nothing left in their GI tract so the doctor can see as clearly as possible with the camera. When done as an outpatient, the ideal bowel prep usually takes at least a few days—if not longer. So even for this woman with the lower GI bleed that GI wants to investigate and diagnose, it’s not as simple as just doing the procedure immediately.

As with most things in the ER, the older you are and the more chronic medical problems you have, the more likely we are to find something that requires hospital admission. Lower GI bleeding is no exception. The younger and healthier you are, the higher the chance we won’t find an exact answer in the ER—and you may leave feeling disappointed.