Cancer patient advocate Melissa Vining said data showing more people were being seen within target timeframes was "very positive", but warned it did not show the bigger picture.
Figures obtained by the Otago Daily Times under the Official Information Act show 90% of urgent colonoscopy cases fell within the two week target recently, up from rates as low as 42% in 2021.
Non urgent rates had also improved.
However, Ms Vining said a major unknown factor was how many patients were not being referred due to rationing and strictly applied access guidelines.
There was no doubt the rationing of colonoscopies had caused clinical and psychological harm for Southern patients, she said.
Some had paid for insufficient government resourcing with their lives.
"The data remains an area of concern to me, particularly ... inaccurate decline rate data and the lack of transparency on wait times for those patients swirling around the alternate pathways."
A health and disability commissioner (HDC) decision released yesterday found the former Southern District Health Board breached standards after a man with terminal colon cancer had to wait 12 weeks for a colonoscopy.
He had four admissions to Dunedin Hospital between April 2018 and October 2019, and met the criteria for an urgent colonoscopy.
"It is incredibly sad to read of the HDC case, my heart breaks for them," Ms Vining said.
However the department was under new leadership and she felt confident much-needed improvements had happened and would continue.
Southland Charity Hospital was set to take patients early next year, and that would be the true test of how many were unable to get help in the public system, she said.
Te Whatu Ora Health New Zealand (HNZ) Southern data showed that between January 2020-June 2023, the number of urgent patients within the two-week colonoscopy target timeframe had increased.
Earlier figures within this timeframe fluctuated heavily, rising to 100% in November 2020 and plummeting to 42% in November 2021.
However, figures provided for this year did not fall below 78%, the most recent being 90%.
Non-urgent Southern cases had also improved, with more patients within the six-week target.
While the figures fell to just 21% in May 2020, the lowest figure this year was 80% and the most recent figure was 96%.
That was significantly higher than the national rate, which ranged between 31-56% and was at 52% in June.
A HNZ spokesman said the data was provisional only.
Regularly publishing wait time data would involve a significant workload increase for staff, but the information was available "on a bespoke basis".
Data on declined colonoscopies was not collated and reported nationally.
The figures provided by HNZ did not include colonoscopies as part of the national bowel screening programme.
"As of June 2023, the national bowel screening programme has a 93% adherence rate to its target timeframe of a patient having a colonoscopy within 60 working days following a positive test result," the spokesman said.
A plan was being developed that would lead to a new national approach.
