How to Know When Bowel Prep Is Complete

Cleaning out the entire colon prior to a colonoscopy is, quite honestly, what has some people running for the hills and avoiding this vital screening exam. Although it is not a pleasant olfactory experience, completing a bowel preparation is not painful.

You want to be sure to stay close to home, however, as you will be using the toilet many, many times before the process is through. But how do you know when your bowel prep is complete?

successful colonoscopy bowel prep
Illustration by Jessica Olah, Verywell

Precautions Before You Begin

Before you begin your bowel prep, make sure you have talked to your doctor if you have any heart, kidney, or liver problems. With some conditions, a physician will need to alter the type of bowel prep you can use. Some treatments are safer than others when it comes to certain medical conditions.

There are many options, so don't worry that you won't be able to have the test done. Making sure the doctor performing your colonoscopy is familiar with your medical history is important for other reasons as well. Some medications, such as blood thinners or other drugs, can increase the risk of complications.

Review Your Instructions

Following your doctor's bowel prep instructions to the letter is very important. Although it may seem like one or more steps are redundant, such as using an enema after moving your bowels numerous times, there's a purpose for the entire process.

Your doctor needs to get every bit of stool cleaned out, which will probably require more than two or three bowel movements. There is a reason why your bowels have to be squeaky clean: It makes it possible for your doctor to see abnormal tissues that might be hidden by bowel contents.

Each gastroenterologist follows the current cleansing guidelines based on evidence, however, each doctor may order the prep a little differently. What your friend's doctor told her to do for a bowel prep might not be the same instructions you receive, and this is normal.

Your doctor will consider your health, what you may or may not be able to tolerate, and what has worked best in the past, prior to instructing you on how to complete your prep.

There are some types of preps that are not advisable with certain medical conditions, and this may account for differences between the prep recommended for you, and that recommended for another.

Getting Started

The majority of bowel preparations begin with a drinkable solution or pills to be taken by mouth. You might start to see effects as soon as 30 minutes to an hour after your first glass of solution or your first pill. Your initial bowel movements will most likely be a combination of firm, semi-firm, or loose brown stools. 

Continue to drink plenty of clear liquids and keep yourself hydrated, keeping in mind to avoid commercial drinks with purple or red dye as the dyes can interfere with your colonoscopy results.

The importance of staying adequately hydrated can't be stated enough, as many of the adverse events related to colonoscopy are related to dehydration. This is especially true with bowel prep products containing sodium phosphate.

You might notice some uncomfortable, but not painful, side effects of the bowel prep. Stomach cramping and gas are common and are a completely normal side effect of forcing your bowels clean. Warm compresses and a small bit of exercise—such as a walk around the house—may help relieve some of the discomforts.

Nearing the Finish Line

When your bowel movements are composed of only brown liquids you are nearing the finish line. The color of your stools should progress to a cloudy liquid, and ultimately, to a yellowish clear liquid. If there is any cloudiness to your liquid stool, your bowel prep is not complete.

If you find that your stools have become clear, liquid, and yellowish prior to completing your entire prep, it's important to finish the prep anyway. Sometimes, stool that is higher in your colon has yet to be expelled, and completing all steps of your prep offers you the best chance of having a clear bowel for your colonoscopy (and not having to repeat the prep).

Why Bowel Prep Matters

According to the American Journal of Gastroenterology, up to 25% of colonoscopies are canceled due to poor bowel prep. Deciding to cancel your procedure is not a decision that is made lightly, especially since you are most likely sedated and the doctor has already started the procedure prior to being able to determine if the colon is clean enough to continue.

If you didn't finish your prep or your bowel movements aren't reduced to clear liquids, contact your doctor so that he or she can help you reschedule your procedure.

There's not really a way to know for sure whether your bowel prep is complete before having a colonoscopy. In fact, it's not uncommon for people to have an incomplete prep which necessitates rescheduling the exam (and repeating the prep!), or doing the exam but perhaps with suboptimal results.

This often occurs, however, when people skip one of the steps of the prep because they believe they are done, or because they don't think all of the steps are necessary. The best way to make sure your bowel prep is complete is by making sure you perform each and every step of the prep as recommended.

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Article Sources
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  2. American Society for Gastrointestinal Endoscopy. Understanding Bowel Preparation. Updated June 2010.

  3. Johnson DA, Barkun AN, Cohen LB, et al. Optimizing adequacy of bowel cleansing for colonoscopy: recommendations from the US multi-society task force on colorectal cancer. Gastroenterology. 2014;147(4):903-24. doi:10.1053/j.gastro.2014.07.002