Combining faecal immunochemical testing with blood test results to identify patients with symptoms at risk of colorectal cancer: a consecutive cohort of 16,604 patients tested in primary care

Structured abstractO_ST_ABSObjectiveC_ST_ABSFaecal immunochemical tests (FITs) are used to triage primary care patients with low risk colorectal cancer symptoms for referral to colonoscopy. The aim of this study was to determine whether combining FIT with routine blood test results could improve the performance of FIT in the primary care setting. DesignResults of all consecutive FITs requested by primary care providers between March 2017 and December 2020 were retrieved from the Oxford University Hospitals NHS Foundation Trust. Demographic factors (age, sex), reason for referral, and results of blood tests within 90 days were also retrieved. Patients were followed up for incident colorectal cancer in linked hospital records. The sensitivity, specificity, positive and negative predictive values of FIT alone, FIT paired with blood test results, and several multivariable FIT models, were compared. ResultsAmong 16,604 eligible patients, 139 colorectal cancers were diagnosed (0.8%). Sensitivity and specificity of FIT alone at a threshold of 10 {micro}g Hb/g were 92.1% and 91.5% respectively. Compared to FIT alone, blood test results did not improve the performance of FIT. Pairing blood test abnormalities with FIT reduced the number of abnormal results needed to detect one cancer but increased the number of cancers missed. Multivariable models retaining FIT, sex, and mean cell volume performed similarly to FIT alone. ConclusionFIT is a highly sensitive tool for identifying higher risk individuals presenting to primary care with lower risk symptoms. Combining blood test results with FIT does not appear to lead to better discrimination for colorectal cancer than using FIT alone.