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

Callum G Fraser ^1*, Catriona M Matthew ¹, N Ashley G Mowat ², John A Wilson ³, Francis A Carey ¹ and Robert JC Steele ⁴

¹ NHS Tayside, United Kingdom
² NHS Grampian, United Kingdom
³ NHS Fife, United Kingdom
⁴ University of Dundee, United Kingdom

^* To whom correspondence should be addressed. E-mail: callum.fraser{at}tuht.scot.nhs.uk.

Accepted 15 February 2007

Abstract

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

Methods A new very simple and stable card collection FIT has been evaluated.

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

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.

Keywords: colorectal cancer, faecal immunochemical test, faecal occult blood test, screening, two-tier approach

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