Faecal occult blood testing for population health screening May 2004

Participation
An important component of any population based screening program is the participation
rate of those targeted for screening. There are many reasons for non-participation in
FOBT screening programs including: intercurrent illness; the lack of appreciation of the
concept of asymptomatic illness; the fear of further tests and surgery; the unpleasantness
of the stool collection procedure and the fear of cancer itself (Hynam et al 1995).
Non-participation in the targeted population negatively impacts on the cost and
effectiveness of the screening program. Since participation may vary between FOBTs
(eg, due to the need to adhere to dietary restrictions), it is important that estimates of the
relative participation rates associated with each FOBT are incorporated into any
assessment of cost-effectiveness. Estimates of the likely participation rates of guaiac
versus immunochemical FOBTs in an Australian population health screening program
were obtained from a study conducted in an Australian average risk population (Cole et
al 2003) and data from the Australian Government Bowel Cancer Screening Pilot
Program (the pilot). The effects of participation rates on the relative cost-effectiveness of
different FOBTs are discussed in the economic section of this report.
Change in clinical management and clinical outcomes
Results
The identification of early stage disease or potential precursors of disease by FOBTs and
subsequent curative procedures such as preventative polypectomy and surgery can
significantly reduce CRC morbidity and mortality. FOBT screening for CRC in the
general population has been shown to reduce CRC mortality in a number of large
randomised and non-randomised controlled trials. A systematic review and meta-analysis
of RCTs performed by the Cochrane Collaboration has shown that screening for CRC in
asymptomatic patients using a FOBT (Hemoccult) can reduce the relative risk of CRC
mortality by around 16 per cent (relative risk 0.84; 95% CI: 0.77, 0.89) (Towler et al
1998).
Diagnostic performance
The accepted methodology for investigating the accuracy of new diagnostic tests is to
compare the diagnosis made with the new test with the true disease status. However, it is
often not feasible to determine the disease status of a patient unequivocally. Therefore, in
many disease states a proxy measure, such as another diagnostic test or clinical
judgement, must be used. The best available measure of disease is called the reference
standard. Both the test result and the comparator result must be independently compared
with the reference standard to assess sensitivity, specificity and accuracy. However, in
studies of screening tests it is often unacceptable and unethical to subject asymptomatic
people with a negative test to what may be a battery of invasive, time-consuming, and
costly clinical investigations.
22 Faecal occult blood testing