What’s a Sigmoidoscopy? All About Testing and Diagnosis

When you have ulcerative colitis (UC), it’s important for your healthcare team to regularly assess inflammation in your colon (large intestine). To do this, it’s necessary to have periodic endoscopic examinations of your colon — procedures in which a scope is inserted to look for signs of disease activity.

The best-known procedure to look at your colon is, of course, a colonoscopy. But an alternative procedure that may be right for some people with UC is known as a sigmoidoscopy. This procedure tends to be quicker and involves simpler preparations, but it’s not appropriate for everyone with UC who requires an endoscopic exam.

Find out how a sigmoidoscopy is different from a colonoscopy, when it’s typically performed in the context of UC, and what to expect before, during, and after the procedure.

Sigmoidoscopy vs. Colonoscopy: What’s the Difference?

The main difference between a sigmoidoscopy and a colonoscopy is how far the scope is inserted into your colon during the procedure.

“The way I describe it to patients is a ‘half-colonoscopy,’” explains Benjamin Click, MD, a gastroenterologist at the UCHealth Digestive Center in Aurora, Colorado. Similar to a colonoscopy, Dr. Click says, a scope is inserted through your anus to examine your anal canal, rectum, and colon. But it’s only extended through the left side of your colon, which consists of the two areas leading up to your rectum: the descending colon and the sigmoid colon.

Because it only involves the last few segments of your colon, a sigmoidoscopy doesn’t require as much preparation as a colonoscopy. “Unlike a colonoscopy, one typically does not have to consume an oral lavage solution to entirely clean out the colon,” Click explains. Instead, he says, most people only require one or two enemas several hours before their sigmoidoscopy to flush out stool from the area.

Another difference is that while sedation is generally recommended for a colonoscopy, it’s typically considered optional for a sigmoidoscopy. “A lot of the unpleasantness in a colonoscopy is from trying to get to the end of the colon,” explains Ashwin Ananthakrishnan, MBBS, a gastroenterologist at Massachusetts General Hospital in Boston.

Of course, the more limited nature of a sigmoidoscopy also carries certain disadvantages. “It’s not able to look at inflammation on the right side of the colon, look for polyps elsewhere, look into your small intestine,” says Dr. Ananthakrishnan. That means not everyone with UC will be an ideal candidate for a sigmoidoscopy as a substitute for a colonoscopy.

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When Is a Sigmoidoscopy Performed for UC?

A sigmoidoscopy may be performed in a number of different situations to diagnose or evaluate your UC.

If your doctor initially suspects that you have UC based on your symptoms and blood tests, you’ll need to have either a colonoscopy or a sigmoidoscopy to have your condition diagnosed. This allows your doctor to look at the inside of your colon, as well as to take a biopsy (tissue sample) that will be examined under a microscope to look for changes typical of UC, along with signs of other health conditions, according to the Crohn’s & Colitis Foundation.

The latest guidelines from the American College of Gastroenterology (ACG) on diagnosing and treating UC, published in 2019 in The American Journal of Gastroenterology, recommend performing a complete colonoscopy to diagnose UC in most cases. This lets your doctor examine the full extent of your disease and make sure that the end of your small intestine isn’t affected, which could indicate Crohn’s disease rather than UC.

But if you have severe disease, the guidelines state that a sigmoidoscopy can be performed instead of a colonoscopy to diagnose UC, since a colonoscopy carries a greater risk of perforation (making a hole in your colon) — a rare but serious risk of both procedures that’s higher when your colon is already more damaged.

The most common use of sigmoidoscopy is to assess your disease activity once you’ve been diagnosed with UC. “Since ulcerative colitis typically starts in the rectum and progresses up through the left side of the colon, we can generally get a pretty accurate assessment” of disease activity with this procedure, says Click.

How often your doctor recommends endoscopic evaluation of your colon (sigmoidoscopy or colonoscopy) depends largely on the severity of your disease, according to Click. “It could be as frequent as every couple of months, or as infrequent as every couple of years,” he notes, with greater disease activity and changes to your treatment both contributing to more frequent evaluations.

Finally, sigmoidoscopy is recommended if you’re hospitalized for acute severe UC. The 2019 guidelines from the ACG state that a sigmoidoscopy should be performed within 72 hours, and ideally within 24 hours, of your admission to the hospital to assess the severity of your inflammation and look for signs of viral infection.

Performing a sigmoidoscopy or colonoscopy early in the course of hospitalization for UC is associated with better outcomes, as shown in a study published in 2016. Researchers looked at data from nearly 85,000 UC-related hospitalizations, in which 67 percent had the procedure within 72 hours and 33 percent had it later. Delaying the procedure was associated with a 76 percent higher risk of death, a hospital stay nearly 3 times as long, and thousands of dollars more in hospital costs.

RELATED: 3 Key Differences Between Crohn’s Disease and UC

What to Expect in a Sigmoidoscopy

Usually, preparing for a sigmoidoscopy is relatively quick and easy and involves just an enema or two that will need to be taken any time from the night before to several hours before the procedure. However, in some cases, your doctor may ask you to follow a special diet the day before your sigmoidoscopy, such as not eating anything and consuming only clear liquids. You may also not be able to eat or drink anything for several hours before the procedure.

You may also be asked to take a laxative the night before the procedure, which may come in pill or liquid form.

When you arrive for the procedure, you’ll be asked to change into a gown and lie on your side on an exam table. If you are having sedation, your doctor will give you the drug and wait for it to take effect.

Your doctor will then begin the procedure, inserting a sigmoidoscope through your anus into your rectum and lower colon. “The procedure itself is fairly quick, 15 to 30 minutes from start to completion,” says Click. But it may take longer “if there is some therapy or intervention that’s needed as part of the procedure,” such as the need to take more biopsies than expected or look more closely at an area or your colon.

If you took sedation for the procedure, you’ll need to have someone accompany you home, and you’ll need to take a few hours off, Click notes. But if you decide against sedation, you can leave on your own and go back to your normal activities right away.

As with any medical procedure, a sigmoidoscopy carries certain risks. These include heart or lung problems in response to sedation, along with bleeding or infection. Each of these risks is less than 1 percent, according to Click. The risk of bowel perforation — potentially the most serious complication — is even lower, occurring roughly once in every 10,000 sigmoidoscopies.

“Overall, the procedure is very well tolerated,” Click emphasizes. “These are done very routinely, and it’s generally a very safe procedure overall.”

Ananthakrishnan recommends sigmoidoscopy instead of colonoscopy for many UC-related examinations. “It’s a good alternative for many with inflammation just in the lower third” of your colon, he notes. “I think patients should be encouraged to consider it more.”