New research examines the best way to use faecal immunochemical test results

The project, funded by our research grants at the University of Dundee, showed that generally, adjusting the threshold used in faecal immunochemical test (FIT) depending on a person’s individual risk wouldn’t improve detection of bowel cancer.

In this research they looked at the impact changing the threshold could have on two groups: those who are taking a FIT test as part of routine bowel cancer screening and those taking one after presenting symptoms.

How is FIT used?

FIT looks for blood in a small sample of poo, which can be a sign of bowel cancer. The result is a number which represents how much blood was in the sample.

It’s the test used for bowel cancer screening across the UK, to identify people who should be sent for further tests like a colonoscopy. GPs can also ask patients who come to them with bowel cancer symptoms to complete a FIT (also known as an ‘at-home test’), to help decide which tests to run next.

In both bowel cancer screening and symptomatic testing there's a number to decide if a person’s FIT is 'positive' or 'negative' this is the ‘threshold’. Making this number lower increases how many cancer cases are detected. But it also increases the number of 'false positives' where someone who doesn’t have cancer is sent for further tests and pressure on colonoscopy services. This means that choosing the right threshold is a delicate balance.

What were the researchers looking at?

This study, led by Professor Robert Steele at the University of Dundee, was to see if the FIT threshold should be changed for different people depending on their other risk factors for bowel cancer. For example, older people have a higher risk of bowel cancer, so should we set a lower threshold for them to be referred for further investigations? 

The researchers considered a range of factors that are known to affect bowel cancer risk, including:

• age
• sex
• socioeconomic status
• bowel cancer screening history
• bowel cancer symptoms and blood test results

These factors were considered, along with their FIT result, to create a way of calculating a person’s ‘risk score’.

This ‘risk score’ was then used in computer models to adjust the threshold for FIT based on a person’s individual risk. They tested to see if this could improve the number of bowel cancer cases diagnosed, and what impact this would have on colonoscopy demand.

They looked at both routine screening (using data from across Scotland) and symptomatic testing (using data from NHS Tayside).

What are their results?

In both bowel cancer screening and symptomatic testing, the team found that the best way to decide who should have further tests is still by using one common threshold on the amount of blood detected by FIT. The computer models using ‘risk score’ to adjust the threshold weren’t any more accurate than the current method.

The results did show one exception to this. They found that there could be some benefit to adjusting the FIT threshold used in bowel cancer screening according to age. Particularly for women, who have a higher rate of bowel cancers diagnosed in between screening tests. However, more work to confirm these findings on a larger scale is required before any changes are made to the screening programme, as well as what effect these changes could have on colonoscopy demand.

• Read their paper about screening here, in the Journal of Medical Screening
• Read their paper about symptomatic testing here, in the journal Colorectal Disease
• Learn more about this research
  
  

Above: A faecal immunochemical test (FIT) as offered in England.
FIT tests appearances vary between nations.