Managing Your Diabetes Before Colonoscopy


For patients with diabetes, any test or procedure that causes you to miss a meal or change your usual meal plan will require special planning to safely manage your blood sugar. Because timing of your meals and medicines will be different than usual, your blood sugar level is also likely to be different that usual and you will want to watch it closely.

General Guidelines:

  • You should check your blood sugars at least 2-3 times on the day before and on the morning of your colonoscopy. Also, check your blood sugars whenever you feel that you might be experiencing either low or high blood sugars.
  • Be sure to tell the nurse, doctor or technician if you think you are having a low blood sugar reaction before or after the procedure. Bring a source of sugar to treat low blood sugar if necessary (i.e., glucose tablets, sugar packets, candy).
  • You should contact your primary care physician/diabetes care provider if your blood sugars are greater than 300 mg/dl.
  • If you have a low blood sugar reaction while preparing for a test, you must treat it. You can use ½ cup apple juice or ½ cup cola (clear liquid with carbohydrate) along with sugar pills/packets/gel if necessary.
  • Keep in mind that low blood sugar levels are potentially dangerous so having slightly elevated blood sugar levels are more acceptable when monitoring your blood sugar and adjusting medications.
  • If it is possible, schedule your appointments earlier in the day so that after the procedure, you may eat and take your diabetes medicine as close to your usual time as possible.

Managing Your Blood Sugar If You Take Insulin:

  • If you take long-acting insulin (NPH, Lente, Ultra-Lente), then you should only take ½ of your usual doses the day and night before and on the day of your procedure.
  • If you take a combination of long-acting plus short-acting insulin (Humalog/Novolog or Humulin/Novolin 70/30, 75/25) or just short-acting insulin (Regular, Lispro), then skip your injections entirely the day before and the day of your procedure.
  • Do Not take any short-acting insulin on the day of your procedure.
  • You may restart your usual insulin does after the procedure has been completed since you will be able to eat normally once again.

Managing Your Blood Sugar If You Take Diabetes Pills:

  • Because you will only be on a clear liquid diet the day before your procedure and fasting after midnight, you should not take your diabetes pills on the day before or on the morning of your procedure.
  • Bring your pills with you and take them as soon as the procedure has been completed since you will be able to eat normally once again.

Clear Liquids:

Clear liquids are all counted as fruit exchanges. You will be replacing all of your carbohydrates (starches/breads, milk, fruit and vegetables) with only simple carbohydrates. These are digested more rapidly and may be more likely to have a low blood sugar reaction. Therefore it is recommended that you take your clear liquids in multiple feedings, not three meals (i.e. drink the liquids at breakfast, mid-morning, lunch, mid-afternoon, dinner, 2-3 hours after dinner and at bedtime). DO NOT take any clear liquids that are RED or PURPLE.

The following clear liquids are recommended:

  • Chicken or Beef Broth 1 cup (0 grams of carbohydrate)
  • Apple Juice ½ cup (15 grams)
  • White Grape Juice ½ cup (15 grams)
  • Jello (not Red or Purple) ½ cup (20 grams)
  • Popsicles (not Red or Purple) 1 cup (30 grams)
  • Kood-Aid (not Red or Purple) ½ cup (10 grams)
  • Carbonated Beverages, not diet ½ cup (10 grams)

*Coffee, tea, broth, clear diet sodas, and water may be taken at any time.

Please note: These are only general guidelines. If there are any other specific questions or concerns, make sure to call your health care provider who manages your diabetes to discuss these issues.

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