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Faecal immunochemical testing (FIT) alone leads to the identification of the same number of patients with colorectal cancer as more complicated approaches that combine the FIT result with the results of commonly used blood tests.

Colorectal cancer comprises >10% of the total UK cancer incidence and disease survival is dramatically improved by early diagnosis. Diagnosis relies on colonoscopy, which has been severely impacted by the COVID-19 pandemic, resulting in a large backlog of patients awaiting investigation for possible colorectal cancer symptoms and consequent delays in cancer diagnoses.

Non-invasive home-based faecal immunochemical tests (FIT) that detect blood in patient stool samples have been recommended by the National Institute for health and Care Excellence since 2017 to guide the referral of patients with unexplained symptoms for colorectal cancer investigation. A previous study by University of Oxford researchers showed that FIT offers an accurate and appropriate triaging method for GPs. However, despite the high reported sensitivity and specificity of FIT for colorectal cancer, nearly 1 in 10 colorectal cancers will be missed using FIT alone to prioritise the highest risk patients for colonoscopy.

With funding from the Oxford Centre for Early Cancer Detection, the team that comprised specialists in primary care, health data science, clinical biochemistry and gastroenterology asked whether additional clinical data could improve the predictive performance of FIT.

 

We are fortunate that the Oxford University Hospitals NHS Foundation Trust was one of the early adopters of FIT and so we had the largest existing cohort of symptomatic patients tested with FIT in primary care in the UK. This rich dataset allowed us to look back at other clinical data such as common blood test results and assess whether combining these results with FIT could reduce the false negative or false positive rates of this test. - Dr Brian Nicholson (Nuffield Department of Primary Care Health Sciences), academic GP and lead researcher of the study.

The team analysed the five most common “core” blood tests (haemoglobin, platelets, white cell count, mean cell haemoglobin and mean cell volume), symptom data, age and sex for 16,604 symptomatic patients in primary care who had undertaken a FIT analysed by the Oxford University Hospitals NHS Foundation Trust between March 2017 and December 2020. Compared to FIT alone, the combination with these additional clinical factors did not improve the performance of FIT for predicting cancer in this population.

 

While using a combination of an abnormal blood test and an abnormal FIT to determine who goes on to colonoscopy would increase specificity and therefore reduce the demand on colonoscopy services, we showed that this approach could increase the rate of cancers missed by 14-fold. This large increase in false negative results would outweigh the benefit of reducing unnecessary referrals. - Dr Diana Withrow (Nuffield Department of Primary Care Health Sciences), lead statistician for the study.

This study suggests that the performance of FIT is not meaningfully improved by the addition of other blood tests in primary care. This gives GPs a clear message to request FIT in patients with symptoms that could be colorectal cancer. Together with other large studies, we are informing national guidance on the use of FIT in GP surgeries. - Dr Brian Nicholson.

As a continuation of this work, the Oxford FIT team will contribute to the COLOFIT programme, funded by the National Institute for Health Research Health Technology Assessment programme led by Professors Colin Rees (University of Newcastle) and Willie Hamilton (University of Exeter). COLOFIT will further assess the optimal use of FIT for patients with symptoms of possible colorectal cancer.

This research is published in BMC Medicine.

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