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Objective: Faecal immunochemical tests (FITs) are used to screen for colorectal cancer (CRC) and as diagnostic aids in symptomatic patients. However, the number of samples per FIT varies. It is unclear if there is any advantage to analyse multiple-sample FITs in symptomatic patients.

Design and setting: This is a post hoc analysis of a retrospective study that included all cases of CRC and adenomas with high-grade dysplasia (HGD) between 2005 and 2009 in the county of Jamtland, Sweden.

Subjects: All patients with CRC and adenomas with HGD that initially presented with symptoms to primary care and delivered FITs.

Main outcome measure: The likelihood of a positive FIT in cases of CRC and adenomas with HGD; when analysing one, two or three samples.

Results: Of 195 patients, 160 delivered three-sample FITs. Using the 139 cases in which at least one sample was positive, the likelihood of detecting a positive sample upon analysis of only one of the three samples was 0.91 (95% CI: 0.85-0.95), indicating that 13 positive cases may have been missed.

Conclusion: Use of a one-sample FIT instead of a three-sample FIT as a diagnostic aid may result in the missing of one tenth of symptomatic CRCs and adenomas with HGD.