For non-urgent tests that needs to be done in 42 days or less, the completion rate is just 21 per cent while the rate for surveillance colonoscopy is 57 per cent in Northland.
Surveillance endoscopy is a check to see if people with a family history of bowel cancer have got the disease.
Northland DHB general manager surgical, pathology and ambulatory services, Andrew Potts, said his staff were committed to reducing waiting times for colonoscopy investigations in line with national standards.
"Waiting times in Northland have been excessive, principally as a result of difficulties in recruiting medical gastroenterologists, of which there is a specialty shortage nationally.
"The lack of a dedicated endoscopy suite at Whangarei Hospital has also been a constraint."
He said NDHB has recently appointed a second medical gastroenterologist which has greatly increased the number of colonoscopies performed at Whangārei Hospital.
The colonoscopy waiting list was now reducing and 79.2 per cent of urgent patients were investigated within 14 days in July, he said.
Potts said the waiting list for non-urgent colonoscopies stood at 492 at the end of August compared with 632 at the end of June and that further improvements was expected in coming months.
NDHB has applied for government funding for a dedicated endoscopy suite at Whangārei Hospital which will contain a second procedure room to increase the number of colonoscopy procedures to be carried out.
"This will be essential to meet the rising demand arising from the fast growing population in Northland and will also enable bowel screening to be implemented from July 2020" Potts said.
Bowel Cancer New Zealand spokesperson Mary Bradley said the statistics for a low socio economic region like Northland were very concerning and illustrated the inequalities in bowel cancer care that existed in the country.
"Everyone should be able to expect a timely bowel cancer diagnosis no matter where they live in New Zealand, whether that is Auckland or Northland. It should not be a postcode lottery, where the diagnosis you receive depends on where you live in the country.
"DHBs are struggling to meet the colonoscopy screening timeframes due to being under resourced and needing additional support from the Ministry of Health which has let the country down by not investing in workforce capacity years ago," she said.
There were 45,000 colonoscopies done in New Zealand last year - an increase of 45 per cent compared to five years ago.
During the same period, referral from doctors has risen 28 per cent.
