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OC-083 Faecal Occult Blood test Analysis in the United Kingdom Bowel Cancer Screening Programme
  1. J Geraghty1,
  2. J Snowball2,
  3. P Butler2,
  4. S Sarkar1,
  5. R Blanks3,
  6. S Halloran2,
  7. C Rees4
  1. 1Royal Liverpool University Hospital, Liverpool
  2. 2Southern Bowel Screening Hub, Guilford
  3. 3Cancer Epidemiology Unit, University of Oxford, Oxford
  4. 4South Tyneside NHS Foundation Trust, South Shields, UK

Abstract

Introduction Increased vascularity of colorectal neoplasia creates bleeding detected by Faecal Occult Blood tests (FOBt). As bleeding is sporadic & unevenly distributed within stools, multiple testing may be required. UK bowel cancer screening programme (BCSP) kits contain 6 windows & subjects returning 5 or 6 positive results are termed “Abnormal” & referred to colonoscopy. If 1–4 windows are positive, the result is initially “Unclear” & 2 further kits are submitted, further positivity leads to colonoscopy (“Weak positive”). If no further blood is detected, subjects are deemed ”Normal” & retested in 2 years.

Aim to study FOBt positivity in detail & whether particular patterns are associated with neoplasia rates that indicate the screening algorithm should be changed.

Methods We selected all subjects from one hub completing 2 screening episodes between 2007–9. Each episode included up to 3 kits and 18 windows. 95 possible combinations were identified. The number of positive windows compared to the total in a given episode was expressed as a “positivity ratio”, ranging from 0–100%. Each combination leading to colonoscopy was analysed. Abnormal (83–100% positivity) & Unclear (11–83% positivity) groups were matched to neoplasia detection rates. Subjects with cancer detected in episode 2 following an Unclear result in episode 1, had their episode 1 pattern analysed.

Results FOBt from 284,387 subjects resulted in 4,000 colonoscopies, diagnosing 286 cancers. The overall cancer rate was 7.1% & adenoma rate 39.9%. The cancer rate was 21.3% in the Abnormal group and 5.8% in the Weak positive group. Cancer detection increased from 1.9–24.5% in linear correlation with increasing positivity of windows, ranging from 11–83% of windows positive. Equivalent percentage positivity rates may or may not lead to colonoscopy depending on the particular pattern. A combination of 4 positive windows in kit 1 followed by 2 normal kits (4NN) equates to a positivity rate of 22% & is currently categorised in the Normal group & doesn’t lead to colonoscopy. Other combinations with 22% window positivity do lead to colonoscopy & a cancer detection rate of 3%. There were 260 subjects with a 4NN combination in episode 1 not leading to colonoscopy & 5 of these subsequently had cancers detected following different combinations in episode 2.

Conclusion This study demonstrates higher ratios of positive windows; detect higher rates of cancer. At present, in the UK some subjects with 11% positive windows proceed to colonoscopy, while others with a rate of 22% (all at kit 1) do not. Based on these findings, further work examining the entire BCSP population, including the costs & benefits of changing the algorithm is in progress.

Disclosure of Interest None Declared

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