Flexible Sigmoidoscopy (FOS)

A flexible sigmoidoscopy involves looking at the lower part of the large bowel (colon) with a narrow flexible tube called a sigmoidoscope (scope).

What is a flexible sigmoidoscopy?

The test involves looking at the lower part of your large bowel (colon) with a narrow flexible tube called a sigmoidoscope (scope). The scope is inserted through the back passage (bottom) and passed around the bowel. The procedure is performed by, or under the supervision of, a trained doctor or nurse (endoscopist). A light and camera at the end of the scope relay pictures onto a television screen. Carbon dioxide is blown into the bowel to inflate it and help the endoscopist see better.

Samples of tissue (biopsies) may be taken during the test. This is done through the scope. It does not cause any pain and the samples are kept to be looked at under a microscope. Photographs may also be taken for your medical records and may be used for teaching purposes.

The procedure generally takes 10 to 20 minutes.

What are the benefits of having a flexible sigmoidoscopy?

If you have been troubled by symptoms the cause may be found and help decide if you need treatment or further tests.

If a polyp is found this can often be removed during the procedure. Flexible sigmoidoscopy may be done as a follow up check if you have had a polyp in the past or other disease of the large bowel.

If a scan or x-ray has suggested there may be something wrong in the large bowel, a flexible sigmoidoscopy allows a closer look at the area.

What are the risks of the procedure?

Complications are rare and may include the following:

Perforation or tear of the lining of the bowel (about 1 for every 1,500 cases). If this happens you may need an operation.

Bleeding may happen where a biopsy is taken or a polyp removed (about 1 for every 150 examinations). This can happen up to 2 weeks after the procedure. It usually stops on its own but may need cauterisation or injection treatment. In some cases a blood transfusion may be needed.

There is a small chance that a polyp or cancer may not be seen (about 5 in every 100 cases). This might be because the bowel was not completely empty or, on rare occasions, that the endoscopist missed seeing it.

In extremely rare cases the procedure can lead to death. Current evidence suggest that this may happen in around one out of every 10,000 procedures.

What are the alternatives?

CT colonography (virtual colonoscopy) is an alternative investigation to flexible sigmoidoscopy. This is carried out in the x-ray department and involves some radiation exposure.

If this test shows there could be something wrong in the bowel a flexible sigmoidoscopy may still be needed to look at the area.

Preparing for the investigation

Home preparation

The lower part of your bowel can be cleared using an enema. This will have been sent in the post or given to you. You should administer this at home two hours before your appointment.

You may eat and drink normally up until the time you have the enema. After that you may have only clear fluids until after the examination.

If you have been given senna tablets in addition to the enema please take these the evening before the procedure.

Hospital preparation

If you feel you will not be able to administer the enema at home, please contact the endoscopy department before your appointment so that we can arrange for it to be given by the nursing staff. There are limited facilities on the unit and if several patients require an enema that day, it may lengthen the time you are in the department or we may have to rearrange your appointment for another date or time.

How long will I be in the Endoscopy department?

Overall you may expect to be in the department for 1 to 2 hours.

What if I take medication?

You should continue your regular medication as normal. However, if you are taking iron tablets you should stop these 5 days before the procedure. If you take Fybogel, Regulan, Proctofibe, Loperamide (Imodium), Lomotil, or codeine, please stop these 3 days before your appointment.

Blood thinning medication (anticoagulants)

Sometimes these medications need to be stopped and if this is the case the person who referred you for the test should have given you clear instructions. If you are unsure please contact your consultant’s secretary. For your safety, if the correct instructions are not followed, it may not be possible to do the procedure and you may have to return on another day.

Warfarin: Unless you have been advised to stop this medication, continue taking it and have your INR checked within the week before the test. The procedure may be cancelled if your INR has not been checked within the last 7 days. It should be within your target range. If you have been advised to stop your Warfarin you should do so for 5 full days before the procedure and have your INR checked the day before the procedure. It needs to be less than 1.5 for the procedure to go ahead. Please bring your yellow book to the appointment.

Dabigatran, Rivaroxaban, Apixaban or Edoxoban: please do not take on the morning of the procedure. If you have been advised to stop taking this medication you should do so for 2 full days before the procedure.

Clopidogrel (Plavix), Prasugrel or Ticagrelor: these medications can generally be continued but if you have been advised to stop you should do so for 5 full days before the procedure.

What happens when I arrive?

When you arrive in the department please book in at reception. It is our aim for you to be seen as soon as possible after your arrival. However, if the department is very busy your appointment may be delayed. The department looks after emergency patients who will be seen first if needed.

A nurse will take you through to the admission room and ask you about your general health to check if you are fit to have the procedure. You will also be asked about your plans for getting home afterwards.

The nurse will make sure you understand the procedure and discuss any further concerns or questions you may have. If you have not already done so and you are happy to go ahead, you will be asked to sign your consent form.

Your blood pressure and heart rate will be checked and you will be asked to remove your lower clothes and put on a hospital gown.

What will happen during the procedure?

The nurse will take you through to the procedure room and you will have the opportunity to ask any final questions. You will be asked to lie on a trolley on your left side with your knees bent and the nurse will place an oxygen monitoring probe on your finger.

The endoscopist may examine your back passage with a gloved finger before inserting the scope. The bowel has natural bends which may cause some discomfort but this should not last long. You may also feel bloated due to the gas that is used.

The endoscopist may ask you to change your position during the procedure as this can help with the passage of the scope.
If you feel you need something to ease any discomfort during the procedure, ‘Gas and Air’ (Nitrous Oxide) is available. This is a gas that you inhale through a mouthpiece. If you have Nitrous Oxide you will need to wait for at least 30 minutes before you can return to normal activities such as driving. If you would like more information please ask the admitting nurse.

What happens after the procedure?

After the procedure you will be taken to the recovery area where you will able to rest if needed. When you are up and dressed the nurse or doctor will explain the findings and if any medication or further tests are required.

What happens if a polyp is found?

A polyp is an overgrowth of cells on the inner lining of the bowel. Polyps may be raised on a stalk like a mushroom (pedunculated) or flat (sessile). Polyps are generally removed or sampled by the endoscopist as they may grow over time and cause problems in the future. This does not cause any pain.


Polyps with a stalk are usually removed using a wire loop (snare) which is placed around the stalk. Heat is passed through the wire which cuts through and cauterises any blood vessels.

Flat polyps are often removed by injecting the tissue around the polyp with fluid to raise the area away from the deeper layers. A hot wire snare is then used to remove the polyp.

Smaller polyps may be removed with a cold wire snare or pinched off the bowel wall with forceps.

Polyps are sent to the lab to be looked at under a microscope. Your consultant may write to you with the results or give them to you at your next clinic appointment if you have one. You may also contact your GP. Results are usually available within 2 to 4 weeks but can sometimes take a little longer.

What are the risks of removing polyps?

After removing a polyp there is a risk of bleeding and/or a hole forming in the bowel wall while the area heals. The healing process can take up to 2 weeks. It is advisable not to travel abroad for this period if large polyps are removed. Please tell the nurse or doctor if you have plans for travel after your procedure.

In most cases you can resume normal activity afterwards but if you have had a large polyp removed you may be advised to avoid heavy lifting or strenuous exercise for 2 weeks to reduce the risk of complications. It is important to attend the accident and emergency department if you pass any fresh blood or clots (more than a few tablespoons) or if you have severe pain or swelling in the abdomen (tummy) which persists and does not get better.

Phosphate enema, directions for use:

  • Lie on your left side if possible with both knees bent, arms at rest
  • Remove the protective shield while holding the bottle upright and grasping the grooved bottle cap
  • With steady pressure, gently insert the enema into your bottom with the tip pointing towards the navel (tummy button)
  • Squeeze the bottle until nearly all the liquid is expelled. Stop if there is any resistance or pain. Forcing the enema can result in injury
  • Stay near to a toilet as the urge to empty your bowel can come on quickly
  • Wait until the urge to use the toilet is strong. This is usually between 2 and 5 minutes.

What must I remember?

If you are not able to keep your appointment please tell the endoscopy department as soon as possible.

  • We will aim for you to be seen as soon as possible after your arrival. However, the department is very busy and your investigation may be delayed. If emergencies occur, these patients will be seen before less urgent cases.

If you have any problems or concerns after administering the enema or you are worried about any symptoms you experience after the flexible sigmoidoscopy, you may ring the enquiry numbers on the front cover of this booklet. Out of hours please contact the NHS non-emergency service on 111.

Frequently Asked Questions:

  • Can I have sedation?
    Sedation is not routinely offered for flexible sigmoidoscopy.
  • Can I return to work after the procedure?
    You may return to work after the procedure if you have not had sedation. If sedation is given then it is advised that you do not return to work for 24 hours afterwards.