Outcomes from colonoscopy following referral from New Zealand general practice: a retrospective analysis

New Zealand has high rates of colorectal cancer (CRC) but poor outcomes. Most patients with CRC are diagnosed following referral from general practice, where a general practitioner (GP) assesses symptoms according to national guidelines. All referred patients are then re-prioritised by the hospital system. The first objective of this study was to identify what proportion of patients referred by general practice to surgical/gastroenterology at Waikato District Health Board (DHB) had a colonoscopy. The second objective was to determine what proportion of these referrals have an underlying CRC and the factors associated with the likelihood of this diagnosis.

This study is a retrospective analysis of e-referral data for patients aged 30-70+ who were referred from 75 general practices to general surgery, gastroenterology or direct to colonoscopy at Waikato DHB, 01 January 2015-31 December 2017. Primary and secondary outcome measures included the proportion and characteristics of patients who were having colonoscopy, and of those, who were diagnosed with CRC. Data were analysed using chi square and logistic regression.

6718/20648 (32.5%) patients had a colonoscopy and 372 (5.5%) of these were diagnosed with CRC. The probability of having CRC following a colonoscopy increased with age (p value < 0.001). Females (p value < 0.001), non-Māori (p value < 0.001), and patients with a high suspicion of cancer (HSCan) label originating from their GP were more likely to have a colonoscopy, while the odds ratio of Māori having a colonoscopy was 0.66 (95% CI 0.60-0.73). The odds ratio of a CRC diagnosis following colonoscopy was 1.67 (95% CI 1.35-2.07) for men compared to women, and 2.34 (95% CI 1.70-3.22) for those with a GP HSCan label. Of the 585 patients referred with a GP HSCan, 423 (72.3%) were reprioritised by the hospital and 55 patients had their diagnosis unnecessarily delayed.

If a GP refers a patient with an HSCan, and the patient receives a colonoscopy, then the likelihood of having CRC is almost 15.0%. This would suggest that these patients should be routinely prioritised without further triage by the hospital. Further research is needed to understand why Māori are less likely to receive a colonoscopy following referral from general practice.