Bowel Screening Pilot results

Data from the Bowel Screening Pilot has been collected since the commencement of Round 1 in 2012. This report summarises data from Round 1 (January 2012 to December 2013), Round 2 (January 2014 to December 2015) and the first nine months of Round 3 (January 2016 to September 2016). This, along with other data, is being used to gauge how well the pilot is working. The information collected in the pilot has been compared with international bowel screening standards to make sure that our pilot is progressing in a safe and effective way.


Summary

Results for people invited in Round 1 of the bowel screening pilot (invited from 1 January 2012 to 31 December 2013), Round 2 (invited from 1 January 2014 to 31 December 2015) and Round 3 (January 2016 to September 2016) are summarised in this report. The results for Round 1 and Round 2 are final. Enough time has passed for people invited in Rounds 1 and 2 to complete the bowel screening pathway. It can take several months for people who are invited to take part to return a completed bowel screening test kit.

Some people taking part in Round 2 and Round 3 had also taken part in Round 1, but some were taking part in the pilot for the first time. International experience shows people who took part in a screening round are more likely to take part in the subsequent screening rounds. People who did not participate in a screening round are less likely to participate in the next screening round. Final results for Round 2 and early results for Round 3 suggest this trend will be mirrored in New Zealand.

During Round 1 the participation for Pacific people has been lower than for other ethnic groups. Final results for Round 2 and initial results for Round 3 indicate that this disparity has lessened during subsequent rounds.

In Round 1, for some people the test kit was proving difficult to complete correctly on the first attempt. The problems did not actually relate to completing the test itself but rather to correctly completing the required documentation. The test kit instructions were revised at the end of Round 1 to make them more easily understood by all population groups, and this has coincided with a notable increase in the number of people successfully completing their kit on their first attempt.

The bowel screening test can detect trace amounts of blood in bowel motions which indicate the need for further investigation. Blood in bowel motions may be caused by cancer, polyps (growths) or other non-cancerous bowel conditions.

If enough blood is found in a test sample to trigger a positive result, participants are offered a diagnostic colonoscopy to check for bowel cancer, or bowel polyps that may develop into cancer over time.

About 6 in 10 people who have a colonoscopy will have adenomas detected. Adenomas may be removed at colonoscopy. Some participants identified with adenomas will be advised to have regular colonoscopy in the future. About 4 in 100 people who have a colonoscopy after their first screening test through the programme will be found to have bowel cancer. For those taking part in Round 2, about 3 in 100 colonoscopies will find bowel cancer. They will be referred for treatment.

How many people have taken part in the bowel screening pilot?

In the first screening round (Round 1) a total of 121,798 people were invited to take part and 69,176 people (%) returned a correctly completed kit (and documentation)  that could be tested by the laboratory.

In the second screening round (Round 2), a total of 130,094 people were invited and 71,810 (%) people returned a correctly completed kit.

In the third screening round (first nine months – 1 January 2016 to 30 September 2016), 48,524 people were invited and 26,621 people (54.9%) returned a correctly completed kit.

The New Zealand participation rate for Round 1 of 56.8% was higher than the internationally acceptable minimum participation rate of 45.0% for first screening rounds.

For Round 2 and Round 3, participants can be divided into three groups:

  • those that are taking part in the screening process for the first time because they have become eligible for an invite (through moving into the area or becoming old enough to participate)
  • those that did not complete a kit successfully in previous rounds or chose not to respond to their previous invites
  • those that successfully took part in one or two previous rounds

The chart below shows the New Zealand participation rate (overall) for people invited during the three screening rounds, and for the three sub-groups of people invited in Round 2 and Round 3.

Participation in the Bowel Screening Pilot
Showing those invited from 1 January 2012 to 30 September 2016

  Round 1 Round 2 Round 3
Participation in the Bowel Screening Pilot
Showing those invited from 1 January 2012 to 30 September 2016
Overall Participation 56.8% 55.2% 54.9%
First screen (ageing or moving in)   46.6% 45.7%
First screen (spoilt or did not respond to previous invites)   25.2% 19.5%
Subsequent screen (successful in one or more previous rounds and invited again)   84.6% 82.4%

Source: Bowel Screening Pilot IT system

The data shows that for all those who received an invite in Round 2, the average participation was 55%. The average participation for the initial nine months of Round 3 is similar, at 55%.

For people for whom Round 2 was their first screen, due to aging in or moving into the area, participation is low (47%). This may be because the average age of a person in this group was 53 and participation is known to be much lower in younger age groups. The initial result from Round 3 shows a similar participation for this group (46%).

For people who were invited in Round 1, but either did not complete their kit correctly or did not take part, only 25% participated in Round 2.

The participation was 20% in Round 3, for people who were invited in Round 1 and/or Round 2, but either did not complete their kit correctly or did not take part. A similar pattern is seen in international data; if a person did not take part in an initial screening round, they are less likely to take part when invited a second time.

For people who successfully took part in previous screening rounds (returning a kit that could be tested by the laboratory) it was very likely that they would return a successful kit in Round 2. The participation rate for this group of people was 85% and this is towards the higher range reported internationally. A similarly high percentage participation was seen for those invited in the first nine months of Round 3 (82%).

Which population groups are most likely to take part in the pilot?

Participation by ethnicity

During Round 1 of the pilot, Pacific people were much less likely to participate than other population groups, but this is less evident in Rounds 2 and 3.

The chart below shows the participation rates, broken down by ethnicity, for people invited in Round 1 and for people invited in Rounds 2 and 3. In addition, the chart shows the data broken down into three sub-groups invited in Rounds 2 and 3.

The chart shows that the participation rate for Pacific people in Round 1 was about half that of the ‘European and Other’ group. The final results for Round 2 and initial results for Round 3 show this gap, while having closed somewhat (possibly in response to a number of initiatives) still remains.

Participation in the Bowel Screening Pilot by ethnicity
Showing those invited from 1 January 2012 to 30 September 2016

  Total Population Māori Pacific Asian European or Other
Participation in the Bowel Screening Pilot by ethnicity
Showing those invited from 1 January 2012 to 30 September 2016
Rd 1 56.8% 46.0% 30.4% 53.7% 59.7%
Rd 2 55.2% 50.7% 39.6% 51.6% 57.2%
Rd 3 54.9% 46.4% 40.3% 52.2% 57.1%
Rd 2 was first screen (ageing or moving in) 46.6% 39.7% 33.5% 47.2% 48.0%
Rd 3 was first screen (ageing or moving in) 45.7% 36.4% 34.4% 45.5% 47.8%
Rd 2 was first screen (spoilt or did not respond to Rd 1 invite) 25.2% 30.7% 27.0% 24.3% 24.8%
Rd 3 was first screen (spoilt or did not respond to previous invites) 19.5% 19.1% 17.7% 22.2% 19.2%
Rd 2 was second screen (successful in Rd 1 and invited again) 84.6% 83.5% 80.5% 80.5% 85.4%
Rd 3 was subsequent screen (successful in one or more previous rounds and invited again) 82.4% 75.2% 75.2% 79.4% 83.6%

Source: Bowel Screening Pilot IT system

Participation by age group and sex

People aged between 50 and 74 years are eligible to take part in the pilot. Those in the younger age ranges are less likely to participate than those who are older. Women are more likely to take part than men, except in the 70–74 age range where participation rates for men and women are almost similar. The chart below shows the participation rate by age group and sex, for people invited in Round 2 and Round 3. Data for people invited in Round 1 show similar trends.

Participation in the Bowel Screening Pilot by age group and sex in Round 2 and Round 3

  Male Round 2 Male Round 3 Female Round 2 Female Round 3
Participation in the Bowel Screening Pilot by age group and sex in Round 2 and Round 3
50-54 41.1% 41.3% 49.1% 49.8%
55-59 47.6% 48.8% 54.3% 54.7%
60-64 55.1% 56.6% 61.8% 60.5%
65-69 63.4% 63.6% 67.7% 67.6%
70-74 72.7% 70.1% 73.7% 70.9%

Source: Bowel Screening Pilot IT system

Participation by socio-economic deprivation

Participation rate also correlates to socio-economic deprivation. The chart below shows that those from the most deprived areas (deprivation grouping 9 & 10) are less likely to participate than those in the least deprived areas (deprivation grouping 1 & 2). We are now considering initiatives that could help improve participation for those in the most deprived groups.

Participation in the Bowel Screening Pilot by deprivation
Showing those invited from 1 January 2012 to 30 September 2016

  Total Population Dep 1 & 2 Dep 3 & 4 Dep 5 & 6 Dep 7 & 8 Dep 9 & 10
Participation in the Bowel Screening Pilot by deprivation
Showing those invited from 1 January 2012 to 30 September 2016
Rd 1 56.8% 60.3% 58.7% 58.6% 49.3% 45.7%
Rd 2 55.2% 58.4% 56.5% 56.7% 48.7% 46.3%
Rd 3 54.9% 58.8% 56.1% 56.0% 48.2% 44.4%
Rd 2 was first screen (ageing or moving in) 46.6% 49.2% 48.2% 47.8% 40.9% 37.5%
Rd 3 was first screen (ageing or moving in) 45.7% 49.0% 46.4% 49.5% 39.7% 34.3%
Rd 2 was first screen (spoilt or did not respond to Rd 1 invite) 25.2% 26.8% 25.3% 25.6% 23.1% 23.0%
Rd 3 was first screen (spoilt or did not respond to previous invites) 19.5% 21.0% 21.0% 19.2% 16.1% 17.5%
Rd 2 was second screen (successful in Rd 1 and invited again) 84.6% 85.3% 84.8% 85.2% 82.3% 82.0%
Rd 3 was subsequent screen (successful in one or more previous rounds and invited again) 82.4% 83.6% 82.8% 82.1% 80.4% 78.3%

Source: Bowel Screening Pilot IT system

How many people are returning a positive test kit?

Participants in the pilot are asked to complete a bowel screening test known as the faecal immunochemical test (FIT) for haemoglobin which detects blood in bowel motions. The FIT is also known as the immunochemical faecal occult blood test (iFOBT), and these names are used interchangeably.

The FIT is sent to a designated laboratory for testing. Where enough blood is found in the sample to trigger a positive result, participants are offered a colonoscopy or other appropriate investigation.

Of all participants who correctly completed their test kit, during Round 1, nearly 8% were reported to have a positive test. This is known as the positivity rate. This is within the expected range when compared with other international bowel screening pilots of this type.

The positivity rates for the groups of people who were invited in Round 2 (between 1 January 2014 and 31 December 2015) and Round 3 (between 1 January and 30 September 2016) are shown in the chart below. These results show similar trends seen internationally.

The positivity rate for people for whom Round 2 or Round 3 was their first screen, due to ageing in or moving into the area, was much lower than the overall positivity in Round 1 (5% for Round 2 and 6% for Round 3 compared to nearly 8% overall positivity in Round 1). This may be due to the average age of the people in this group being 53. Younger age groups are less likely to have a positive FIT result than older age groups.

Positivity of kits returned in the Bowel Screening Pilot
January 2012 to September 2016

  Round 1 Round 2 Round 3
Positivity of kits returned in the Bowel Screening Pilot
January 2012 to September 2016
Overall Positivity 7.5% 5.9% 5.5%
First screen (ageing or moving in)   5.2% 6.1%
First screen (spoilt or did not respond to previous invites)   8.5% 7.2%
Subsequent screen (successful in one or more previous rounds and invited again)   5.4% 5.1%

Source: Bowel Screening Pilot IT system

In Round 2, for people who were invited in Round 1, but either did not complete their kit correctly or did not take part, positivity was nearly 9% – higher than the overall positivity in Round 1. The value for the comparable group in Round 3 was 7%.

For people who successfully took part in one or more previous screening rounds (returning a kit that could be tested by the laboratory), positivity was lower than the overall positivity in Round 1 (around 5% for both Rounds 2 and 3).

In conclusion, it is expected that positivity will be high in the first screening rounds as participants have not been screened before. After the first screen, participants who have had a positive test and a subsequent colonoscopy are not invited for the next screening round. Hence a lower positivity is expected in the subsequent screening rounds.

Are there any problems with the returned kits?

Not everyone is completing the bowel screening test kit correctly on their first attempt, meaning some kits cannot be analysed. This is usually because the test has not been labelled correctly – only a small proportion are because the test been performed incorrectly. These are known as ‘spoilt kits’.

Of all the first kits sent out between 1 January 2012 and 31 December 2013 (Round 1), approximately 14 percent were spoilt on the first attempt. This figure dropped to 6 percent early in Round 2 and coincided with the introduction of new test kit instructions and other revised information for participants. Most people went on to complete a kit correctly, once another kit was sent to them. For the first nine months of Round 3, 5.2% of kits were spoilt on the first attempt.

The likelihood of a spoilt kit increases with the participant’s age. Some ethnic groups have higher rates of spoilt kits. This situation is being monitored.

How many colonoscopies have been performed?

About 8,400 people have had a colonoscopy (or a Computerised Tomographic Colonography – CTC if indicated for medical reasons) through the Bowel Screening Pilot. These people had all completed a test kit which was reported as positive.

Participants are generally being offered a colonoscopy within 11 weeks of the laboratory identifying that their test was positive. This timeframe is an important indicator of how well the pilot is working. It is being monitored closely.

CTCs make up less than two percent of all diagnostic tests performed following a positive FIT result.

How many people have had cancer detected?

At the point at which the BSP data was extracted (31 March 2017), 340 people had a cancer detected through a colonoscopy delivered as part of the Bowel Screening Pilot in Round 1, Round 2 and Round 3. A further 35 people had their cancer detected after returning a positive FIT and choosing to have a colonoscopy through a private provider. This is a total of 375 people being identified with cancer. More than one cancer was found in some people. 

Of the 375 people who were diagnosed with cancer, 214 people were found to have cancer following an invitation during Round 1 (192 found publicly and 22 found privately), 120 people were found to have cancer following an invitation in Round 2 (108 found publicly and 12 found privately) and 41 people were found to have a cancer following an invitation in Round 3 (40 found publicly and 1 found privately).

The number of cancers found is at the lower end of the range of what would be expected when compared with international bowel screening programmes. The cancers are being detected at an earlier stage than you would expect in a normal clinical setting where people visit their doctor because they have symptoms.

When a cancer is diagnosed, the participant is referred on for appropriate treatment and care. However, in approximately ten percent of cases, the cancer detected is confined within a polyp that was removed at colonoscopy and therefore surgery is not required.

In addition to finding cancers, the pilot is also detecting many non-cancerous polyps called adenomas, which grow on the wall of the bowel. These adenomas are removed at colonoscopy but despite this, some participants with adenomas will still be at increased risk of developing more adenomas or bowel cancer. These participants will require regular bowel checks by colonoscopy (surveillance) in the future.

Is the complication rate for colonoscopy what should be expected?

Sometimes complications arise following a colonoscopy especially if a participant has had a large polyp, or a large number of polyps, removed from their bowel during the procedure.

Of those people who received a colonoscopy between 1 January 2012 and 31 December 2013 50 participants were admitted to hospital to have further treatment or monitoring within 30 days of undergoing a colonoscopy within the pilot.

Between 1 January 2014 and 31 December 2015, 38 participants were admitted to hospital to have further treatment or monitoring within 30 days of undergoing a colonoscopy within the pilot.

Between 1 January 2016 and 30 September 2016, 15 participants were admitted to hospital to have further treatment or monitoring within 30 days of undergoing a colonoscopy within the pilot.

Most of these admissions were for complications that were not considered to be serious and involved a short stay in hospital for observation.

More serious complications such as perforation of the bowel or bleeding usually result from interventions performed to remove polyps. The number of these intermediate and more serious complications is about what is expected given the number of participants identified as having polyps. Admission to hospital is an important quality measure and is monitored closely.

The Bowel Screening Pilot’s monitoring indicators

A detailed set of monitoring indicators has been drawn up to monitor and evaluate the progress of the pilot. The results for Round 1 and Round 2 are now considered final. Results for Round 3 relate to any person invited between 1 January and 30 September 2016.  Round 3 will be completed in December 2017, but results will not become final until approximately September 2018, this is to allow all invitees enough time to return their kit and complete the bowel screening pathway.

The monitoring indicators are published online at Bowel Screening Pilot Monitoring Indicators.

Additional analyses

Additional analyses looking at the positivity, detection rates and positive predictive values by ethnicity are published online at Positivity, positive predictive values and detection rates by ethnicity.

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