Optimal diagnostic accuracy of quantitative faecal immunochemical test positivity thresholds for colorectal cancer detection in primary health care: A community‐based cohort study

BACKGROUND: Optimizing colonoscopy resources is challenging, and information regarding performing diagnostic quantitative faecal immunochemical test (FIT) in daily clinical practice in primary health care is still limited. This study aimed to assess the sensitivity, specificity, positive predictive value and negative predictive value of varying FIT positivity thresholds on colorectal cancer (CRC) detection in primary health care. METHODS: A retrospective cohort study of 38,675 asymptomatic and symptomatic patients with a FIT (OC‐Sensor™) performed between 2012 and 2016 in a primary health‐care setting, using a clinical laboratory database of two Spanish areas linked with the National Health System's Hospital Discharge Records Database. The primary outcome was 2‐year CRC incidence. RESULTS: The mean age of the participants was 63.2 years; 17,792 (46.0%) were male. CRC prevalence was 1.7% (650/38,675). The percentage of patients with a FIT result above the threshold was 20.7% and 14.6% for 10 μg Hb/g faeces and 20 μg Hb/g faeces thresholds, respectively. Sensitivity was 90.5% (95% confidence interval 88.0%–92.5%) at a 10 μg Hb/g faeces threshold, and this decreased by 3.1% when a 20 μg Hb/g faeces threshold was used. The negative predictive value for CRC was at least 99.2% in any subgroup analysed. At a 20 μg Hb/g faeces threshold, less than one additional CRC would be missed per 1000 patients investigated, while approximately 1.3 times more colonoscopy examinations were needed to identify an incidence of CRC using the lowest threshold for any situation analysed. CONCLUSIONS: In primary health care, a quantitative FIT threshold should be tailored to colonoscopy capacity and CRC prevalence in specific populations.