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Navigating a Colonoscopy with Diabetes: Advice and Guidance

By Cheryl Alkon

Most people have to undergo a colonoscopy at some point in their lifetime. If you are a person with diabetes, it is important to know how you should prepare for this test and how to manage your blood sugars before, during, and after the procedure.

Whether you’ve reached your 50th birthday or have had symptoms that suggest colon or rectal problems, be prepared to have a healthcare professional order you a colonoscopy at some point in your life. 

A colonoscopy is the most reliable test to prevent and detect colorectal cancer (hopefully catching it in its earliest stages). It uses a tiny camera to examine the colon (also called the large intestine) and rectum via a long flexible tube known as a colonoscope. People are typically sedated to minimize discomfort, while a healthcare professional guides the tube through their rectum and colon, looking for growths, called polyps, that aren’t supposed to be there. Healthcare professionals can remove polyps during the procedure and test them to see if they are harmless, precancerous, or cancerous. 

This critical test can prevent you from developing cancer – which is particularly important for people with diabetes. A 2015 study found that people with type 2 diabetes were at a slightly higher risk for developing colorectal cancer, and this risk increased for people who also had obesity for four years or more.

The Centers for Disease Control and Prevention recommends adults between the ages of 50 and 75 get regular colonoscopies, and then as recommended by your healthcare professional for people over the age of 75. Colonoscopies can be done earlier in life if you have a family history of colorectal cancer, or you experience symptoms such as stomach pain, ongoing constipation or diarrhea, or bleeding from your behind. It’s possible that your healthcare team may suggest other tests for colorectal screening – learn more about these here.

If your healthcare professional wants you to schedule a colonoscopy, make sure you discuss the details surrounding diabetes management with them first, said Tami Ross, a spokesperson for the Association of Diabetes Care & Education Specialists (ADCES) and a diabetes population health specialist. “Talk with your primary care provider and endocrinologist (if you have one) about the best plan for you to manage your blood glucose before, during, and after the test,” she said. “Any medical test that causes you to miss a meal or change your usual eating plan requires prior planning to keep your blood glucose from becoming too high or dropping too low.” 

It’s important to follow all guidelines about how to eat a few days before the test, how to prepare your body for it, and how to fully recover from the procedure, which typically takes place in a medical office.

The Importance of Preparation

Be sure to speak with your healthcare team about what preparation for your colonoscopy will include. Some healthcare professionals ask people to eat a specific diet a few days before their procedure and to drink a certain medicated liquid the day before the test, causing you to empty your bowels often and completely. Other healthcare professionals prefer that people eat a low fiber-diet for breakfast and lunch, followed by a clear fluid dinner, and then half the bowel-emptying medication the night before the procedure. The next day, they take the other half of the medication three or four hours before the procedure. With this second method, people “usually don’t go hungry and they don’t feel as nauseated and can better consume and tolerate the preparation; hence, less of an effect on their blood sugars,” said Ala Sharara, a professor of medicine at the American University of Beirut and a consulting professor at Duke University Medical Center. 

“When you make your appointment for the colonoscopy, mention you have diabetes,” said Ross. “Ask for any specific instructions, and have a list of all your medicines, doses, and when you take them in case there are any questions.” 

When scheduling, pick a morning appointment instead of an afternoon slot, Sharara advised. This minimizes the time spent fasting during the day so “you can get back as soon as possible to your normal routine for eating and taking medicines,” said Ross. However, afternoon appointments may be preferable for people who have to travel a long way to the endoscopy center, but know you’ll have to fast and manage your blood glucose the entire time before the test.

“It is critical to achieve an adequate – and preferably an excellent – bowel preparation,” said Sharara. If the colon is not fully cleared, the test is less likely to find any potential problems. It could also result in having to undergo the test and preparation a second time, which can be inconvenient and costly.

Diabetes Adjustments

The healthcare professional who oversees your diabetes care will have specific instructions to help you before, during, and after the procedure. However, it’s important that people with diabetes avoid their blood sugars going too low, said Sharara. Ross agreed and added, “You may need to alter your diabetes treatment before and after the procedure.” 

Because there are so many different combinations of diabetes medications, it’s difficult to provide broad guidance. However, Ross and Sharara provided these general guidelines:

  • If you take oral medications, you may be told to pause them on the day of the exam.

  • If you take metformin, your provider may tell you to stop taking it for two days before and two days after your colonoscopy.

  • If you’re on short-acting insulin, you may be told to skip it the day of the procedure – at least until you eat afterwards.

  • If you take long-acting insulin, you may be counseled on how to modify your dosing (sometimes by as much as half) before the test.

  • And finally, “Make sure you work with your healthcare team on what plan is right for you,” Ross said.

If you don’t have a continuous glucose monitor, check your blood glucose regularly while preparing for a colonoscopy: before meals, at bedtime, the morning of the procedure (every few hours) and any time you feel you might be running high or low. “Bring your blood glucose records from the previous 12-24 hours with you to the test, along with your diabetes supplies and hypoglycemia treatment,” said Ross.

If your blood sugar goes low either while you are preparing for the colonoscopy or the day of the exam, take 15 grams of carbohydrates (such as clear apple juice, white grape juice, or six ounces of regular sweetened clear or lemon-lime soda), as long as this is done two or more hours before the appointment, said Sharara. If you prefer to use glucose tabs, talk to your healthcare professional to see if it is okay to use three or four of those that aren’t either red or purple, said Ross.

If you have type 1 diabetes and your glucose readings are above 240 mg/dl, it’s important to test for ketones, said Ross. If ketones are moderate or large, contact your healthcare professional for further guidance.

The Day of the Test and Afterwards

During the test, you will likely be put under anesthesia, and as a result, you’ll likely be asked to come to the exam with a friend or family member who can drive you home. Plan to stay home the rest of the day after the procedure, but people can usually be up and about after two to four hours, said Sharara.

“Take your diabetes medicine with you to the colonoscopy to take after the test as your healthcare professional suggests,” said Ross, but don’t take a double dose of the medications you have missed. “Your healthcare team may have you track your blood glucose more closely during the two to three days after your test to make sure things are back on track,” she said.

Finally, do everything you can to manage your blood sugar levels and follow the directions to fully prepare for the test. “Traditionally, diabetes has been identified as a risk factor for an inadequate preparation,” said Sharara. This can be caused by several factors, including being less likely to eat a low-fiber or mostly liquid diet ahead of time, not fully following the bowel cleansing preparation, “and possibly delayed motility in some people with advanced or long-standing diabetes,” he said. Such people, who have chronic constipation, may be advised to eat a low-fiber diet for two to three days or take additional laxatives to fully empty the bowels. 

However, “everyone is different,” said Ross. “Talk with your healthcare professional about the best plan for you, and get the instructions in writing so you don’t have to try to remember everything.”

About Cheryl

Cheryl Alkon is a seasoned writer and the author of the book Balancing Pregnancy With Pre-Existing Diabetes: Healthy Mom, Healthy Baby. The book has been called “Hands down, the best book on type 1 diabetes and pregnancy, covering all the major issues that women with type 1 face. It provides excellent tips and secrets for achieving the best management” by Gary Scheiner, the author of Think Like A Pancreas. Since 2010, the book has helped countless women around the world conceive, grow and deliver healthy babies while also dealing with diabetes.

Cheryl covers diabetes and other health and medical topics for various print and online clients. She lives in Massachusetts with her family and holds an undergraduate degree from Brandeis University and a graduate degree from the Columbia University Graduate School of Journalism.

She has lived with type 1 diabetes for more than four decades, since being diagnosed in 1977 at age seven.

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