Faecal occult blood testing for population health screening May 2004

Safety
2000, making it second only to lung cancer as a cause of cancer deaths nationally in 2000
(AIHW and AACR 2003). Approximately five per cent of Australians develop CRC
during their lifetime; half of these people die from the disease within five years of
diagnosis.
FOBTs are used as a screening test for the identification of CRC. This is based on the
use of faecal occult blood as a marker for CRC. However, an inherent problem with the
technology is that many other non-neoplastic disease processes can cause GI bleeding.
Therefore, the sensitivity and specificity of a test for the detection of blood will not
necessarily translate into equivalent accuracy for the detection of CRC in a population
health screening setting. Positive FOBT results due to other GI diseases will give a
reduction in the expected specificity of the technique as a CRC screening measure.
Immunochemical tests are expected to be less susceptible than guaiac tests to this effect,
since only lower GI bleeding is detected.
FOBTs are non-invasive and therefore unlikely to cause adverse events. However, the
use of FOBTs in a screening setting is likely to increase the number of colonoscopies,
sigmoidoscopies and barium enemas performed in the screened population. Therefore,
the increased numbers of adverse events associated with these procedures are important.
A 1997 review of six prospective studies estimated that around 1 in 1000 patients suffer
perforation, 3 in 1000 suffer major haemorrhage and between 1 and 3 in 10,000 die as a
result of colonoscopy (Winawer et al 1997). A 1989 review of nine studies of diagnostic
colonoscopy gives a slightly higher figure of around 1.7 in 1000 patients suffering
perforation and similar figures for haemorrhage and death (Habr-Gama and Waye 1989).
The risk of perforation and haemorrhage increases with the performance of
polypectomy. There are also other occasional serious complications associated with
bowel preparation prior to colonoscopy or the use of sedation in conjunction with this
procedure.
Perforation rates associated with sigmoidoscopy appear low and occur in less than 2
cases per 10,000 examinations (National Health and Medical Research Council
(NHMRC) 1999). Serious complications associated with double contrast barium enema
(DCBE) also appear rare and have been estimated at 3 per 10,000 tests, with a death rate
of 3 in 100,000 tests (Winawer et al 1997).
The Minnesota (US) randomised controlled trial (RCT) of FOBT screening for CRC
reported a perforation rate of 0.03% (4/12,246) and a rate of serious bleeding of 0.09%
(11/12,246) in association with colonoscopy (Mandel et al 1993). The Nottingham (UK)
FOBT trial reported a rate of 0.5% (7/1474) for colonoscopy complications and no
complications of DCBE, from a total of 1778 subjects receiving follow-up (Robinson et
al 1999). There were no colonoscopy related deaths reported in either trial.
Concern has also been expressed about the psychological impact of CRC screening, and
this is an important issue. However, detailed exploration of this would require a
dedicated systematic review and a cost-effectiveness comparison incorporating qualityof-life
measures, which is beyond the scope of this review.
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