International comparisons with New Zealand’s bowel screening programme
(A document detailing the evidence from the Pilot programme which informed decision making on the age range and screening test threshold for the NBSP is available on the Ministry of Health website.)
More than 700,000 people will be invited for screening every two years once the programme is fully implemented throughout the country.
Those invited to take part in the National Bowel Screening Programme will be sent a screening test called a faecal immunochemical test (FIT), which they complete at home. They then return it in a pre-paid envelope for laboratory testing.
Faecal immunochemical test (FIT)
The FIT can detect tiny traces of blood in faeces, which can be an early warning sign of bowel problems. The amount of blood present in a test sample must reach a specific threshold in order for the test to be considered positive, or abnormal.
Pilots and ongoing programme evaluations consider FIT positivity thresholds and eligible age ranges against key outcomes such as bowel cancer detection rates, and the number of colonoscopies needed to detect a bowel cancer to best balance the risks and benefits for participants and to determine overall impact of demand on resources, especially colonoscopy capacity.
England, Scotland and Northern Ireland initially limited the eligible age groups to 60–69 years, a pragmatic step that reflected colonoscopy shortage and the screening age group recommended by the United Kingdom National Screening Committee.
FIT thresholds vary between countries. As colonoscopy capacity cannot be increased rapidly, countries such as Canada and Australia have designed their programmes to align with initial colonoscopy capacity. Setting a higher FIT positivity threshold results in higher-risk individuals being referred to colonoscopy and is the most effective way to reduce colonoscopy demand.
When a test is positive, further investigation – in most cases colonoscopy – is offered. The positivity level refers to the percentage of returned tests that fall above the threshold and are considered positive or abnormal. A FIT positivity rate of between 5–8% has been suggested as optimal to minimise missed cancers and advanced adenomas.
New Zealand’s FIT threshold is similar to the Netherlands and is expected to give a similar positivity level of around 7%. The Australian screening programme also reports a positivity level of approximately 7% at their FIT threshold. In other words, about 7 out of 100 people who participate will receive a positive result. Screening programmes in the United Kingdom initially used the older guaiac faecal occult blood tests, but the immunochemical FIT is now being introduced. To maintain similar positivity rates of around 2%, higher thresholds for positivity are initially proposed.
- New Zealand’s bowel screening programme will be offered to those aged 60 to 74 who are eligible for publicly funded healthcare.
- New Zealand’s FIT threshold is 40 ug Hb/g faeces (200 ng Hb/ml buffer).
- The positivity level is expected to be around 7%, based on an anticipated participation rate of 62%.
- The National Bowel Screening Programme will develop a clear plan and timetable to monitor outcomes during the phased introduction of the national programme. This will include reviews of cancer detection rates and colonoscopy capacity to ensure that when possible, programme adjustments – including changes to the FIT threshold for positivity and age range – can be made to allow the detection of more cancers.
- A phased roll out, which started in 2014, will see all 55 to 75 year olds invited to take part in screening every two years from 2018.
- Half way through 2014, the programme raised the FIT cut-off from 15ug up to 47 ug Hb/g faeces.
- The decision to raise the FIT cut-off was because the national programme encountered higher than expected participation rates and higher FIT positive / referral rates than their pilot. This resulted in an overwhelming demand on colonoscopy.
- The Netherlands’ current threshold is similar to New Zealand’s level, and gives a similar positivity level of 6.7%.
- When Australia first rolled-out their programme they limited screening to a very narrow age range to limit costs and to match service capacity, with only those turning 55 and 60 years initially invited to screening.
- Australia will have taken 15 years to extend their programme to biennial screening for those aged 50 to 74, ie by the end of 2020.
- The Australian programme threshold has been reported to be 100 ng Hb/ml buffer or 20 ugHb / g faeces.
- The programme screening positivity rate is around 7%.
- Bowel screening in England is offered to those aged 60 to 74.
- England is changing to using FIT in 2017.*
- They will likely set their FIT threshold around 150 to 180 ug Hb/g faeces to achieve an expected positivity rate of about 1.8%.
- Scotland offers bowel screening to those aged 50 to 74.
- Scotland is also changing to screening using FIT.* They have set their FIT level at 80 ug Hb/g faeces.
- This FIT threshold gives a 2.4% positivity rate.
*Note: England and Scotland currently use a different test for detecting blood in faeces, but are changing to the FIT as it is easier for people to collect the sample and is a more accurate test.
1. Flitcroft KL, St John DJ, Howard K, et al. A comparative case study of bowel cancer screening in the UK and Australia: evidence lost in translation? Journal of Medical Screening 2011; 18(4): 193-203.
2. Wilschut JA, Habbema JD, van Leerdam ME, et al. Fecal occult blood testing when colonoscopy capacity is limited. Journal of the National Cancer Institute 2011; 103(23): 1741-51.
3. van Hees F, Zauber AG, van Veldhuizen H, et al. The value of models in informing resource allocation in colorectal cancer screening: the case of The Netherlands. Gut 2015; 64(12): 1985-97.
4. Moss S, Mathews C, Day T, et al. Increased uptake and improved outcomes of bowel cancer screening with a faecal immunochemical test: results from a pilot study within the national screening programme in England. Gut 2016; Online first June 7, 2016.
5. Steele RJ, McDonald PJ, Digby J, et al. Clinical outcomes using a faecal immunochemical test for haemoglobin as a first-line test in a national programme constrained by colonoscopy capacity. United European Gastroenterology Journal 2013; 1(3): 198-205.