Many patients throughout the country are waiting longer than they should for a colonoscopy to detect bowel cancer.
Just over half the country's 20 district health boards are meeting the requirement that 90 percent of patients needing urgent colonoscopy tests receive them within two weeks.
But many are falling behind in delivering timely diagnosis for one of the country's major cancer killers.
Data released to RNZ under the Official Information Act shows how each of the country's 20 DHBs rates for the Health Ministry's requirement that urgent, non-urgent and surveillance colonoscopies be delivered within certain timeframes. It covers April, May and June this year.
The 12 boards meeting the targets on urgent colonoscopies are Auckland, Capital and Coast, Hutt Valley, Lakes, MidCentral, Tairāwhiti, West Coast, Bay of Plenty, Counties Manukau, Hawke's Bay, Taranaki, and Waitemata.
Just 63 percent of patients needing the urgent tests at Nelson-Marlborough DHB and 75.7 percent in Northland get them within two weeks.
Nine DHBs provide 70 percent of non-urgent colonoscopy tests within the required six weeks or less. Those at the bottom of this scale are Northland DHB (21 percent), Hutt Valley (37 percent) and Taranaki (39 percent).
For surveillance colonoscopies, needed for those who lack symptoms but are at higher risk of bowel cancer, half the DHBs meet the requirement to provide 70 percent of these tests within 12 weeks or less. At the bottom in this group are Nelson Marlborough DHB (21 percent) and Hutt Valley (34 percent).
The Ministry of Health says the data shows an increasing awareness of bowel cancer symptoms and was a positive result for the rollout of the National Bowel Screening Programme.
"The increased demand for colonoscopy services indicates people are paying more attention to their bowel health. This is a great outcome for the NBSP but it is posing challenges for DHBs who have not yet built the capacity to meet that demand."
It said almost 43,000 colonoscopies were carried out in New Zealand last year, which is 13,000 more than in 2013, a 45 percent increase. Referrals for all outpatient colonoscopies rose 28 percent over the period.
Susan Parry, clinical head of the screening programme, said the ministry was talking to medical colleges and the ministry's team responsible for leadership on workforce issues about how to further boost staff needed to deliver more colonoscopies.
The Bowel Cancer New Zealand group, however, called the new data evidence of a "postcode lottery" in access to vital health services.
"Bowel Cancer New Zealand has been calling for an increase in colonoscopies and endoscopists for nearly a decade now," spokesperson Sarah Derrett said.
"What is happening, we're seeing it play out in these data with large proportions of people waiting much longer than they should be to have colonoscopies.
"What's being done to address that problem?"