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The Ministry of Health does not have an appropriate way to estimate the demand for colonoscopy, University of Otago epidemiologist and screening authority Associate Prof Brian Cox says.
He questioned why there had been no detailed audit of the possibly spurious methods being used which he said was fundamental before they were used in any monitoring capacity.
Prof Cox was commenting on the ministry's answers, released under the Official Information Act, to questions posed about the number of colonoscopies district health boards were expected to deliver in the year to the end of June 2018.
Southern DHB's figures showed that in the same year as the board began bowel screening, it delivered 653 fewer colonoscopies than the 3644 it was expected to deliver.
However, population health and prevention deputy director general Deborah Woodley said it could not be assumed the board had "under-delivered" because the model used to determine the numbers for each board, based on standardised intervention rates, was "a guide rather than a highly accurate predictor of the number of colonoscopies that would be performed in any given population".
With this system, each board population is standardised to take into account age, ethnicity, deprivation and sex.
(The figures are only for colonoscopies performed on symptomatic patients and do not include those from the bowel screening programme. To the end of June this year, SDHB had completed 887 colonoscopies since joining the programme in April last year.)
The total number of interventions/colonoscopies is estimated across the country and then each DHB is given its expected proportion. The figures for the year to June 2018 showed nine of the 20 DHBs had not delivered their expected numbers.
Ms Woodley said this did not indicate whether the total number for the country was the "right" number, nor did the methods boards used for accepting referral for colonoscopy.
There could also be a variation in how boards classified colonoscopies.
"This is just one tool a DHB can use to assess demand and rates of delivery. It is important these figures are not used in isolation to form assumptions about patient access."
Other considerations included a board's knowledge of local needs, demands for specific services and the contribution of the private health market in their population.
There would always be variation across the country, in line with different population mix and pressures.
"With finite resources it is important that DHBs prioritise their resources so they can best support those patients with the greatest level of need and potential to benefit from assessment and/or treatment."
This variability in the DHB data covering all colonoscopies, medical, surgical, inpatient and outpatient had led to the development of colonoscopy wait time indicators (CWTI). These were purely a measure of outpatient colonoscopy services, she said.
This CWTI data, published monthly, was included in the readiness assessment that was undertaken before a DHB could join the bowel screening programme.
It had always been made very clear that the provision of timely colonoscopy services, for both symptomatic patients and bowel screening participants, was a key component for the safe delivery of the National Bowel Screening Programme (NBSP) she said.
CWTI figures released last month show that for April, May and June this year, Southern District Health Board did not meet the standard that 90% of those accepted for an urgent colonoscopy receive the procedure in 14 days or less. In April the percentage was 88.9%, in May 87.5% and June 88.2%. Waiting times set for non-urgent colonoscopies and surveillance colonoscopies were met.
Prof Cox said with the degree of variation between DHBs unknown, regarding how they classified colonoscopies, the CWTI tables provided little capacity to monitor DHB capability to keep up with screening demand.
"As appears to have been the case in the SDHB, greatly restricting access to the point that patients suffer delayed diagnosis of bowel cancer possibly leading to unnecessary death, increases the proportion having their urgent colonoscopy within the target."
Urgent cases which were denied colonoscopy were excluded from the denominator for the CWTI calculation but should be added, he said.
The CWTI tables do not include numbers of people referred for colonoscopy and denied it.
Commenting on a letter to the ODT this week from former ministry chief medical adviser David Geddis suggesting that intervention rates for colonoscopy were better in Southern than in Canterbury, Prof Cox produced spreadsheets compiled from ministry data for five years (each to the end of September). They covered all public colonoscopies, including those undertaken in the NBSP.
They showed that the adjusted colonoscopy rates for Southern were below Canterbury in 2015, 2016 and 2017 and only slightly exceeded Canterbury last year, due to increased referrals from bowel screening, which began earlier that year. Canterbury has not yet joined the programme.
"In addition, the private sector in the SDHB region probably provides fewer colonoscopies than the Canterbury region, so the relative colonoscopy rate is likely to be lower than appears from the comparison of public hospital rates," Prof Cox said.