The Health Ministry is strongly defending a decision to exclude people in their 50s from the rollout of national screening for bowel cancer.
The government announced in May last year that it would spend $39 million over the next four years to roll out - from July this year - national screening for bowel cancer to those aged 60 to 74.
New Zealand has one of the highest bowel cancer rates in the developed world; 3000 people are diagnosed a year and about 1200 die.
National screening has been long awaited by doctors and patients alike.
And the wait reflected the major hurdles of being able to deliver the number of diagnostic colonoscopy procedures needed under national screening, and the acute awareness of officials and others that screening any group of apparently healthy people for a serious disease must be safe, accurate and reliable.
Screening for bowel cancer will be only the third national cancer screening programme offered in this country. The other two are breast and cervical cancer screening. It follows a successful four-year pilot screening programme in Waitemata, where those aged 50 to 74 were screened. From December they will transition into the national programme.
But the restricted age range and a change to a faecal occult test (formerly an iFOBT, now called FIT) used in the pilot have sparked worries for the Bowel Cancer New Zealand group.
Under the pilot, any FIT test result that reached 75 nanograms of blood per milliliter of solution was deemed a "positive result" and would earmark that person for a follow-up colonoscopy.
That FIT threshold will be set at 200 nanograms per milliliter under national screening.
Bowel Cancer New Zealand said the lower threshold used in the Waitemata pilot was cost-effective for New Zealand taxpayers.
"The decision to raise the threshold will mean fewer cancers and adenomas [pre cancers] will be detected, and that people will continue to unnecessarily die."
And the decision to change the age-range means "unnecessary deaths from bowel cancer will continue to be a burden for New Zealanders aged 50 to 59.
"Over 300 New Zealanders are diagnosed with bowel cancer in their 50s each year."
Ministry defends age-range, threshold settings
In documents on its website, the Ministry says the age-range screened in the pilot was broad by international standards.
It says the test threshold was set at an intentionally low level in the pilot as well, compared to international screening practices.
"This approach provided critical insights that were used to develop new parameters for a New Zealand national bowel screening programme."
The Ministry's bowel cancer clinical director, Susan Parry, defended the age change, but left open suggestions in officials' papers that it could be altered later.
"I think what we need to do to be responsible, and what most countries do is that once they have rolled out bowel screening to the initial age group, then they regroup, they look at what has happened to the colonoscopy capacity.
"They look at the performance of the screening test and the screening programme, and then they review to see if they should change the parameters."
Dr Parry said New Zealand was doing nothing differently, and that the UK began by rolling out screening to those aged 60 to 69.
"We wanted to go for as wide a range as we possibly could. Ireland started out with 60 to 69. Australia started out with five-year age bands and is still not fully rolled out."
She said the test change was also appropriate.
"[In the pilot], a lot of the colonoscopies were being performed between the reading of 75 and 200, but a lot of those colonoscopies were not detecting bowel cancer or significant polyps, and that's not good for wise use of [the] colonoscopy resource, and it's not good for those patients."
Dr Parry confirmed screening will begin in Hutt Valley and Wairarapa in July.
She said next up would be the Counties Manukau and Southern district health board areas, in the first half of next year. Waitemata would transition into the national programme this December. DHBs would need to pass an assessment before they get a go-live date.
The screening programme is now part of the Ministry's National Screening Unit, and Dr Parry said it was envisaged that all FIT tests under the national programme would be processed by one lab.