Replicate and repeat faecal immunochemical tests in symptomatic patients: A systematic review.

BACKGROUND: Faecal Immunochemical tests (FITs) in the assessment of patients presenting with symptoms have generally used a single sample. Little evidence pertains to the use of replicate, where a number of tests are done prior to decision-making or repeat FIT, where additional FIT are performed following clinical decision-making. Overwhelmingly, research has focussed on FIT to help identify colorectal cancer (CRC). The aim of this review is to assess the available literature concerning replicate and repeat FIT in symptomatic patients to help generate consensus and guide future research. METHODS: The terms 'faecal immunochemical test' or 'FIT' were combined with 'multiple' or 'repeat'. EMBASE, Medline and PubMed database and other searches were conducted. All papers published in English were included with no exclusion date limits until November 2021. RESULTS: Of the 161 initial papers screened, seven were included for review. Qualitative and quantitative FIT outcomes were assessed in the studies. The primary aims of most related to whether replicate FIT increased diagnostic yield of CRC, with colonoscopy used as the reference standard. One publication assessed the impact of a new COVID-adapted pathway on CRC detection. No consensus on replicate FIT was apparent. Some concluded that FITs may help minimise missed CRC diagnoses: others showed no increase in diagnostic yield of CRC. CONCLUSIONS: Current evidence on replicate and repeat FIT is both minimal and conflicting. FIT is a superb clinical tool, but significant gaps surrounding application remain. Further studies relating to replicate and repeat FIT are required.

An observational study of replicate faecal immunochemical tests in the urgently referred symptomatic cohort.

INTRODUCTION: Triage of patients with suspected colorectal cancer (CRC) utilises a single faecal immunochemical test (FIT) at a defined threshold. Limited evidence exists regarding whether replicate FIT improves the positive and negative predictive value in symptomatic patients. This study examines urgently referred symptomatic patients undergoing replicate FIT. Primary aim is to assess two FITs and CRC/serious bowel disease. Secondary aims are to determine correlation and utility of replicate FIT. METHODOLOGY: Patients carried out one additional FIT during COVID-19 pandemic. FIT 1 and FIT 2 (the replicate sample) were analysed in relation to symptoms, diagnoses, investigations, future colonoscopy and missed CRC. Study period was 01/03/2020-31/07/2020. Three subgroups were compared; double positive (≥10 µg Hb/g faeces), double negative, and discordant FIT (one positive). RESULTS: 111 patients had replicate FIT (50 male, 61 female). 43 (38.7%) patients had double negative, 32 (28.8%) double positive and 36 (32.4%) had discordant FITs. Median time between FITs was 14 days (IQR = 11-19). 83% of double positive patients underwent colonoscopy/virtual colonoscopy (61% in double negative patients). Six CRC and one high-risk polyp were in double positive patients (none in other groups). One discordant patient was not investigated and a CRC missed. CONCLUSIONS: Replicate FIT as a triage strategy appears most effective where both FITs are negative. CRC risk is low when FIT results are discordant. Double negative FITs are reassuring given benign associated diagnoses, or for patients where endoscopic investigation is high-risk. Larger studies are required to evaluate discordant FITs, enabling refinement of urgent investigation pathways.