Effect of dietary restriction on participation in faecal occult blood test screening for colorectal cancer.

OBJECTIVES

To determine if participation in colorectal cancer screening using faecal occult blood testing (FOBT) is affected by a restrictive diet and if it is associated with certain demographic variables.

PARTICIPANTS AND

SETTING

1,203 residents of South Australia aged 50-69 years, with no "currently active bowel disease", randomly selected from a database of people willing to be contacted about unspecified health issues.

DESIGN

Randomised controlled trial: participants were offered screening by immunochemical FOBT by mail in 1998. Half were randomly allocated to a group instructed to follow a low-peroxidase diet, as required for guaiac FOBT, while the other group was not so restricted.

MAIN OUTCOME MEASURES: Effect of diet restriction on participation (return of correctly completed FOBT sample cards within 15 weeks); time taken to return cards; relationships between participation and demographic variables.

RESULTS

Participation rates were 65.9% (no-diet group) and 53.3% (diet group) (difference, 12.6%; 95% CI, 7.1%-18.1%). In the first week, rates of return as a proportion of all tests returned were 13.1% (no-diet) and 1.6% (diet) (difference, 11.5%; 95% CI, 8.6%-14.4%), increasing to 54.3% and 44.5%, respectively, after five weeks (difference, 9.8%; 95% CI, 4.2%-15.4%). Participation was significantly associated with older age (odds ratio, 1.40; 95% CI, 1.10-1.78), but not sex, Index of Social Disadvantage or rural versus urban address.

CONCLUSIONS

Dietary restrictions create a barrier to FOBT-based screening for colorectal cancer. The use of immunochemical rather than guaiac FOBT removes this barrier.