Unmet need is growing in New Zealand, with more than 170,000 Kiwis in need of surgery but not on a waiting list.

Thousands of people are being left off surgery waiting lists across the country, and Canterbury may have the highest level of unmet need.

About 174,000 New Zealanders are in need of publicy-funded surgery, but have not been placed on a waiting list, new research from global research company TNS shows.

Patients are commonly being turned away as their pain is not considered to be severe enough, or GPs are "waiting to see" how their condition progresses.

The research showed Auckland and Christchurch as having the highest demands for elective surgery, but Canterbury Charity Hospital founder Phil Bagshaw says his data shows unmet need is higher in Canterbury.

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Bagshaw has been trying to measure the level of unmet need in the region since late last year.

Preliminary findings from the study have shown 8 per cent of Aucklanders who require surgery are not "registered by the system", and 10 per cent of Cantabrians.

The Charity Hospital had just purchased a neighbouring property to expand its services as a direct result of increased demand.

It would use the extra space to expand its dental service, among others, and reshuffle its administration office.

Bagshaw's survey relied on people picked at random off the electoral roll, and stratified into groups to accurately present a wide sample of the population.

The Government's method of measuring unmet need by contacting GPs was "misleading", he said.

"Our study has shown it's a complete waste of time. A large proportion of the population now don't go to their GP because they can't afford it. It's no longer just my opinion because we have figures to support it," he said.

Bagshaw's study was several months away from completion as the full set of results needed to be collated and reviewed. He hoped to use the study to support an application to the Health Research Council for funding for a "much bigger study".

Patients in need of surgery were ranked by their pain and assigned a number – they only made it on to the waiting list if their number was high enough to meet five different criteria thresholds.

According to the research – conducted on behalf of the Health Funds Association of New Zealand and the New Zealand Private Surgical Hospitals Association – waiting times for surgery had increased significantly.

The wait for a publicly-funded surgery had leapt by 80 days since 2013, to 304 days.

About 350,000 adult New Zealanders had some form of elective surgery each year. A further 280,000 were told they needed surgery, but only 110,000 were placed on the waiting list.

The average time it took a person to get from their GP to surgery was 177 days in the public health system, and just 76 days in private.

​The data was gathered through an online survey, with 125 participants from each of the country's 10 biggest district health boards (DHBs). A sample of 500 was gathered from across the other DHBs.

Ministry of Health electives and national services manager Clare Perry said New Zealand had an ageing population, and people were living longer.

"As a result, elective surgery is increasing every year in New Zealand and it remains a priority for the health system."

Just over 167,000 elective surgeries were carried out in the 2014-15 financial year, up 41 per cent from five years earlier.

Perry said some aspects of the research by TNS, such as waiting times, did not correlate with data the ministry collected directly from DHBs.

"There's been considerable effort in developing and applying clinical prioritisation tools on the basis that patients with the greatest need and potential to benefit from surgery receive it first. Income is not a factor," she said.

In a statement, Health Minister Jonathan Coleman said the only answer to increased demand was to do more – "and that's what we're doing".

Between July and September last year, only 4 per cent of people referred by their GPs for a first surgical assessment were declined.

"It's expected that as the data builds the number of patients declined and sent back to their GP for care as they didn't meet the threshold will rise to around 10-15 per cent," he said.

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UNMET NEED IN 2016

Average time from GP to surgery: 177 days in public health system, 76 days in private.

Of those on waiting lists, 63 per cent are waiting for publicly-funded surgery, and 13 per cent for ACC. Only 7 per cent are funded by health-insurance.

More than half of privately-funded surgeries are completed within a month.

Waiting times for surgery have increased by 80 days since 2013, to 304 days.

Only 19 per cent of those waiting receive publicly-funded care or assistance

Those living on lower household incomes are more likely to require elective surgery

The most common form of elective surgeries is gynaecology, followed by gastrointestinal, knee and shoulder surgeries.

(Source: TNS)