Is dietary restriction always necessary in Haemoccult screening for colorectal neoplasia?

Certain dietary constituents may cause guaiac-based faecal occult blood tests to be positive in the absence of blood loss. In a randomized controlled study of Haemoccult screening for the early detection of colorectal cancer, a policy of retesting with appropriate dietary restriction is used to minimize false-positive results. Delay associated with the retesting protocol may cause considerable anxiety. The aim of the study was to determine the likelihood of an initial positive result remaining positive after retesting. One-hundred-and-thirteen of 137 (35.6%) subjects whose initial test was < 5 squares positive remained positive in contrast to 52/59 (88.1%) with > or = 5 squares positive, a significantly higher proportion (P < 0.001). This suggests that if five or more test squares are positive, then dietary interference is unlikely to be responsible. We conclude that, if dietary restriction retesting is practiced, individuals with strongly positive tests may be offered investigation without retesting, thus reducing their delay to further investigation.