COLORECTAL CANCER

Evaluation of a card collection-based faecal immunochemical test in screening for colorectal cancer using a two-tier reflex approach

Callum G Fraser¹, Catriona M Mathew¹, N Ashley G Mowat², John A Wilson³, Francis A Carey⁴, Robert J C Steele⁵

¹ Scottish Bowel Screening Centre Laboratory, Kings Cross, Dundee, UK
² Department of Gastroenterology, Aberdeen Royal Infirmary, Foresterhill, Aberdeen, UK
³ Department of Gastroenterology, Victoria Hospital, Kirkcaldy, Fife, UK
⁴ Department of Pathology, Ninewells Hospital and Medical School, Dundee, UK
⁵ University Department of Surgery and Molecular Oncology, Ninewells Hospital and Medical School, Dundee, UK

Correspondence to:
Professor C G Fraser
Scottish Bowel Screening Centre Laboratory, Kings Cross, Dundee DD3 8EA, UK; callum.fraser{at}nhs.net

Background: The guaiac faecal occult blood test (gFOBT) has been proved as a screening investigation for colorectal cancer, but has disadvantages. Newer faecal immunochemical tests (FITs) have many advantages, but yield higher positivity rates and are expensive. A two-tier reflex follow-up of gFOBT-positive individuals with a FIT before colonoscopy has been advocated as an efficient and effective approach.

Methods: A new simple and stable card collection FIT was evaluated.

Results: 1124 individuals who were gFOBT positive were asked to provide samples. 558 individuals participated, 320 refused and 246 did not return samples. No evidence of sampling bias was found. 302 individuals tested FIT negative and 256 tested positive. In the 302 FIT-negative individuals, 2 (0.7%) had cancer and 12 (4.0%) had large or multiple (high-risk) adenomatous polyps. In contrast, of 254 positive individuals, 47 (18.5%) had cancer and 54 (21.3%) had high-risk polyps. 93 (30.8%) of the FIT-negative individuals had a normal colonoscopy, but only 34 (13.4%) of the FIT-positive individuals had no pathology. Sensitivity, specificity, and positive and negative likelihood ratios (and 95% CIs) for cancer were 95.9% (84.8 to 99.3), 59.2% (54.7 to 63.5), 2.35 (2.08 to 2.65) and 0.07 (0.02 to 0.27), and for cancer and high-risk polyps were 87.8% (80.1 to 92.9), 65.3% (60.6 to 69.7), 2.53 (2.19 to 2.93) and 0.19 (0.11 to 0.31), respectively.

Conclusions: A two-tier reflex screening algorithm, in which gFOBT-positive participants are tested with a FIT, is effective in identifying individuals at high risk of significant colorectal neoplasia. This strategy is transferable across different FIT formats. This approach has been adopted for the Scottish Bowel Screening Programme.

Abbreviations: FIT, faecal immunochemical test; gFOBT, guaiac faecal occult blood test; Hb, haemoglobin

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