Fast track — ArticlesImmunochemical testing of individuals positive for guaiac faecal occult blood test in a screening programme for colorectal cancer: an observational study
Introduction
Randomised trials have shown that regular annual or biennial screening with a guaiac faecal occult blood test (FOBT) significantly reduce deaths from colorectal cancer.1, 2, 3 On the basis of this evidence, a pilot study was established in the UK to assess whether a national screening programme for colorectal cancer was feasible.4 The results of this pilot have shown that screening with guaiac FOBT is feasible within the context of the UK's National Health Service (NHS) and that screening should reduce deaths from colorectal cancer.5
However, this type of screening is imperfect. First, guaiac FOBT has fairly low clinical sensitivity and specificity.6 Second, independent assessment of the pilot study highlighted that most positive guaiac FOBT results arose from repeat testing of initially weak positive tests, which increased the screening period for many participants, and might be overly burdensome in a national screening programme. For these reasons, attention has been given to alternative tests.7 The choice of FOBT for screening is not easy, however, and recommendations from WHO and the World Organisation for Digestive Endoscopy (OMED) suggest that no extensively studied FOBT meets the needs for all target populations worldwide.8 Interest in the use of immunochemical FOBT has increased, and evidence suggests that this test, by use of one or preferably two samples of faeces, has better clinical sensitivity than does guaiac FOBT.8 Moreover, because immunochemical FOBT is specific for human haemoglobin, no dietary restriction is needed.
Immunochemical FOBT is more expensive than is guaiac, and has a lower limit of analytical detection, leading to a substantially higher frequency of positive results than guaiac—factors that might place unacceptable burdens on a publicly funded screening programme. To overcome these issues a two-tier approach has been suggested,9 in which faecal samples for both guaiac FOBT and immunochemical FOBT are obtained simultaneously without dietary restriction. A positive guaiac FOBT is confirmed or refuted by use of the immunochemical FOBT; however, obtaining faeces for both FOBT at the same time might hinder implementation of this procedure. As suggested previously,10 but to our knowledge not studied to date, we aimed to assess a two-tier approach in the second round of the Scottish group in the UK pilot study of screening for colorectal cancer. All participants with a positive guaiac FOBT were offered immunochemical FOBT before colonoscopy. We did an observational study to assess whether testing individuals who were positive on guaiac FOBT with immunochemical FOBT could direct investigation, by use of colonoscopy, to those most likely to have neoplastic pathology.
Section snippets
Methods
All participants in the final 13 months of the second round of the Scottish group in the UK pilot study of screening for colorectal cancer who had a positive guaiac FOBT were offered colonoscopy.4, 5 The UK pilot was coordinated from England (in Coventry and Warwick) and from Scotland (in Tayside, Grampian, and Fife). The population invited for screening in every round were individuals aged 50–69 years; the population invited in the first round (2000–02) was much the same as that for the second
Results
Table 1 shows the number of participants by interview location, sex, age, and guaiac FOBT positivity. 1486 potential participants attended for interview with specialist nurses. 801 sets of samples were returned and, of 800 with consent, 173 (22%) were N/N, 129 (16%) were N/P, and 498 (62%) were P/P.
We found no evidence of sampling bias. The number of men and women who returned samples was much the same, as was median age and range (table 1). For those with availavble data, 368 (46%) of 799
Discussion
We have shown a positive relation between strength of positivity on guaiac FOBT and the results of immunochemical FOBT. Most participants classed as strong positive on first guaiac FOBT were P/P on immunochemical FOBT, compared with about half of those classed as positive on the third guaiac FOBT; those classed as positive on second guaiac FOBT were intermediate between these two groups.
Our findings suggest that the small number of individuals who are strongly positive on first guaiac FOBT
References (15)
- et al.
Randomised controlled trial of faecal-occult-blood screening for colorectal cancer
Lancet
(1996) - et al.
Randomised study of screening for colorectal cancer using faecal occult blood test
Lancet
(1996) - et al.
Choice of fecal occult blood tests for colorectal cancer screening: recommendations based on performance characteristics in population studies: a WHO and OMED report
Am J Gastroenterol
(2002) Colon cancer screening guidelines 2005: the fecal occult blood test option has become a better FIT
Gastroenterology
(2005)- et al.
Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study
N Engl J Med
(1993) - et al.
A demonstration pilot trial for colorectal cancer screening in the United Kingdom: a new concept in the introduction of healthcare strategies
J Med Screen
(2001) Results of the first round of a demonstration pilot of colorectal cancer screening in the United Kingdom
BMJ
(2004)