In line with other international bowel screening programmes, the amount of blood needed to trigger a positive result (positivity threshold) will be set at a level where there is a greater likelihood of a cancer being found in those who go on to have a colonoscopy.
While colonoscopy is considered a safe procedure, as with most medical procedures, there is a risk of complications. The positivity threshold chosen will minimise the number of screening participants who undergo this invasive procedure with no serious problems then found.
The eligible age range and the positivity threshold differ from those used in the pilot. This is because the parameters for the pilot were intentionally broad in order to gather as much information as possible about critical factors, including the optimum age range for a national programme, the acceptability of the test and the positivity threshold that would best balance cancer detection with colonoscopy capacity.
Most European countries with an organised screening programme use a non-invasive test that detects the presence of blood in faeces. Those which have started their programmes more recently (including Ireland and the Netherlands) are, like New Zealand, using the newer immunochemical faecal occult blood test known as FIT.
Some countries use flexible sigmoidoscopy as part of their screening programme. This involves a limited direct examination of the lower portion of the large bowel). No countries use it as the sole screening test.
At this stage the Ministry, its clinical and professional multidisciplinary advisory groups and international advisers believe there is no indication to change the screening test to flexible sigmoidoscopy.
This is a view shared by a number of experts who produced a paper published in the New Zealand Medical Journal in June of this year, titled Screening for colorectal cancer: spoiled for choice?
They found that FIT tests perform better than flexible sigmoidoscopy in reducing the incidence and mortality from bowel cancer, and in likely screening coverage.
The Ministry of Health regularly reviews new developments and the experiences of other countries in screening tests and population based screening programmes. Our focus is on delivering a high quality national screening programme which is safe and effective, and results in fewer New Zealanders losing their lives to bowel cancer.
• Dr Susan Parry is an associate professor, gastroenterologist, and clinical director of the Ministry of Health's bowel cancer team. Further information on the national screening programme is available on the Ministry of Health website: www.health.govt.nz
