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Bowel cancer, also known as colorectal cancer, is treatable and curable if caught early. NHS England’s Bowel Cancer Screening Programme aims to find warning signs in people aged 60 to 74.

They are invited to take a faecal immunochemical test (FIT) every two years. FIT measures blood in faeces and people with levels above a certain threshold are invited to have their bowel tissue examined for signs of cancer. Growths which could become cancerous (polyps) are removed and cancers prevented.

Researchers were surprised to find that the FIT threshold for further investigation is set at a point that may miss more than half of bowel cancer cases. This highlights a need to improve the NHS screening programme.

They suggest that the programme could make better use of FIT’s ability to provide the exact concentration of blood in faeces (rather than only whether it is above or below a cutoff level).

A new, multi-threshold strategy would mean referring people different follow-up according to their results. Screening intervals could be varied, and different ways of examining the bowel could be used (for example, sigmoidoscopy examines only the lower bowel). This could reduce the number of cancers missed while minimising the demand on services. 

More information about NHS England's bowel screening programme can be found here.

What’s the issue?

Bowel cancer affects the colon and rectum. It usually begins in clumps of cells called polyps on the inner lining of the bowel. Although some polyps go away, others slowly develop into cancer. 

Bowel cancer is the fourth most common cancer in the UK and more than 16,000 people die from it every year. But it can be successfully treated if spotted early: most people diagnosed at the earliest stage survive.

NHS England’s Bowel Cancer Screening Programme (NHS BCSP) offers bowel cancer screening every two years to people aged between 60 and 74. A kit is sent in the post for people to use at home and then return. The test looks for blood in poo (faeces), which can be a sign of polyps or bowel cancer. People who receive an abnormal result are invited for a further test (colonoscopy) in which a tiny camera is passed inside the bottom (rectum) to examine bowel tissue for signs of cancer.

The current test for blood in faeces is the FIT (faecal immunochemical test). This replaced the previous test, the guaiac faecal occult blood test (gFOBT) following a successful initial (pilot) study in 2014 comparing the two. 

The gFOBT test gave two results: negative or positive. FIT is more informative and gives the amount of blood in faeces. But FIT screening is routinely used in the same way as gFOBT, with a single cut-off threshold (of 120μg/g). 

The current screening programme with FIT therefore has only two screening pathways: 

    • people with results above the threshold are referred for further investigation (usually a colonoscopy)
    • people with results below the threshold are offered another FIT test two years later.

The researchers wanted to see if FIT results could be used more fully to improve screening. They wanted to estimate how many cancers were being missed among people with results below the threshold. And they wanted to examine whether looking at graded results – not just a single threshold – could be used to introduce new screening pathways.

What’s new?

The researchers used data gathered as part of the 2014 pilot study which included 27,238 people. Of these, 1,825 had a FIT result of 20μg/g or higher, and they had colonoscopy to detect bowel cancer and polyps. 

The research team used this data to develop a model to show how different FIT results relate to the risk of cancer or polyps in the bowel.  

The model suggests that the current bowel cancer screening programme may miss a high proportion of cancers and high-risk polyps. It found that the current threshold of 120μg/g:

    • is likely to miss more than half of bowel cancer cases (51%)
    • identifies one in four high-risk polyps (25%). 

A much lower threshold of 20μg/g could identify more (82%) of bowel cancers and high risk polyps (64%) but would mean that many more of those screened (7.8%) would be referred for colonoscopy. This is not practical because of the limited number of specialists to carry out the procedure. 

The researchers suggest instead that new screening pathways could be introduced. Different FIT results would determine the screening interval and/or the investigations used. 

Why is this important?

These findings highlight the need to improve the national screening programme for bowel cancer. Using a low FIT threshold in the NHS screening programme would demand far more colonoscopies than is currently realistic. 

The researchers therefore suggest that the screening programme could make use of FIT results to develop multi-threshold screening pathways. The programme could make use of less invasive or more widely available diagnostic tools such as flexible sigmoidoscopy (only the lower part of the bowel is examined) and capsule colonoscopy (people swallow a tiny camera which passes into the bowel). Methods like these could help identify high-risk individuals without overloading the colonoscopy service. 

In a multi-threshold approach, different concentrations of blood found in faeces would trigger different actions. An example of the screening pathways could be:

    • blood is undetectable - next screen is delayed to three years 
    • very low blood concentration - next screen at standard interval of two years
    • low blood concentration - screening is repeated at three months 
    • medium blood concentration - flexible sigmoidoscopy, removal of polyps plus a further FIT to ascertain whether the cause of the bleeding has been removed 
    • high blood concentration - standard colonoscopy.

The thresholds for each pathway will need to be established before new screening pathways could be introduced.

What’s next?

This research highlights an opportunity to improve the detection of bowel cancer and high-risk abnormalities currently identified by the NHS bowel cancer screening programme in England. 

The researchers have suggested that FIT results could be used more fully as part of a programme with multiple screening pathways. But further research is needed to work out the safety and effectiveness of this proposal, and to establish specific thresholds for each pathway.  

This study did not take into account detailed information about polyps, such as where they were found in the bowel. Future work should examine this because it influences the amount of blood found in faeces and is associated with the risk of developing bowel cancer.

You may be interested to read

The full paper: Li S J, and others. Faecal Immunochemical Testing in Bowel Cancer Screening: Estimating Outcomes for Different Diagnostic Policies. Journal of Medical Screening 2020;28:3 

Related research about faecal testing: Toes-Zoutendijk E, and others. Incidence of interval colorectal cancer after negative results from first-round fecal immunochemical screening tests, by cutoff value and participant sex and age. Clinical Gastroenterology and Hepatology 2020;18:7

Related research about faecal testing: Niedermaier T, and others. Diagnostic performance of flexible sigmoidoscopy combined with fecal immunochemical test in colorectal cancer screening: Meta-analysis and modeling. European Journal of Epidemiology 2017;32 

Bowel Cancer UK; the UK's leading bowel cancer charity.


Funding: NIHR Research Methods Fellowship 2017 and the NIHR Policy Research Programme, conducted through the Policy Research Unit in Cancer Awareness, Screening and Early Diagnosis.

Conflicts of Interest: The study authors declare no conflicts of interest.

Disclaimer: NIHR Alerts are not a substitute for professional medical advice. They provide information about research which is funded or supported by the NIHR. Please note that views expressed in NIHR Alerts are those of the author(s) and reviewer(s) and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.

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Study author

We expected to find evidence that bowel cancer screening in England has room for improvement, but we were surprised by the high proportions of cancers and high-risk adenomas (polyps) likely to be missed. 

The current tactics of screening are to test for faecal blood and follow up with colonoscopy in those whose faecal blood content exceeds a single cut-off point. It’s a “one size fits all”. The multi-threshold management strategy explored in this study challenges this approach. A multi-threshold management strategy could go some way to addressing the limited availability of colonoscopy. In addition, further investigations short of colonoscopy might be more acceptable to many people.  

We did not recommend a particular strategy in our paper because how to best use FIT and what tools to use alongside it are highly dependent on healthcare resources. In bowel screening in England, the FIT referral threshold is set according to the capacity for colonoscopy, and this is limited due to the number of specialists able to perform it. So, while we would aim to maximise detection of cancer, we must also minimise the burden on colonoscopy.

Joy Li, Doctoral Student, Queen Mary University of London

Bowel Cancer UK

The Bowel Cancer Screening Programme is one of the best ways to diagnose bowel cancer early, or in some cases prevent it from developing in the first place. We know that screening saves thousands of lives each year, however more can still be done to make the programme even more effective. 

This research is exciting and adds to the growing body of evidence that the future of screening will be personalised based on an individual’s risk. But further research needs to be done to understand how we can do this in a safe and effective way. 

In the meantime, to improve the effectiveness of the screening programme the Government and NHS must work towards fully implementing the UK National Screening Committee recommendation so everyone aged 50-74 is sent a FIT kit every two years, and is tested at the most sensitive threshold. To make this a reality, they must increase capacity in endoscopy and pathology services by using the Spending Review to provide multi-year long term funding to train more staff in cancer services.

Genevieve Edwards, Chief Executive, Bowel Cancer UK

Lived experience 

I refused a screening test in 2016 because I was preparing for orthopaedic surgery. At the time, I felt unable to take what I had always found to be a distasteful but very necessary test. The following year, following a sudden manifestation of bowel cancer symptoms, I underwent successful surgery to remove part of my bowel. 

The cancer was at an early stage, and I did not need chemotherapy or radiotherapy. But I felt then, and still do, that my bowel cancer might have been detected earlier if I had taken up the offer of a screening test. This was a learning experience for me and serves as a lesson for others. 

This paper argues convincingly in support of rationalising the use of resources while still safeguarding patient outcomes. I hope that this research raises awareness and leads to a greater take-up of the screening test by people in the target age group.

Ann Whitfield, Public Contributor, Carlton, Nottingham


This is an interesting study and highlights the number of bowel cancers and high-risk polyps that are potentially missed by the threshold used in the Bowel Cancer Screening Programme. The research suggests that a more complex, stratified approach would reduce the risk of missing people with cancers or high-risk polyps. 

An assessment of the practicality of this more complex approach is needed, along with a detailed cost analysis. The impact of these proposals would have to be balanced against the need for increased resources. For example, this approach would require greater administrative input and would be very likely to increase the workload of endoscopy and pathology departments, with more polyps and cancer biopsies to be examined.

Adrian Bateman, Pathologist involved in bowel cancer screening, University Hospital Southampton

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