Role of dietary restriction in Haemoccult screening for colorectal cancer.

The aim of this study was to investigate the effect of dietary restrictions on the positivity rate and yield of neoplasia during a study based on Haemoccult screening for colorectal neoplasia. Of 18,925 participants who completed Haemoccult tests on a normal diet, 647 (3.4 per cent) were positive. All repeated the test with dietary restrictions: 251 remained positive and underwent further investigations which revealed 35 carcinomas and 169 adenomas in 129 subjects. The remaining 396 were sent a further Haemoccult test at 3 months. Of these, 317 (80.1 per cent) completed the test: 31 (9.8 per cent) were positive. Further investigation of the 31 positive subjects revealed four carcinomas and 20 adenomas. Retesting with dietary restriction will reduce the false positive rate of Haemoccult when used for colonic cancer screening. However, if the retest is negative a further test should be performed. To minimize the adverse effect this may have on compliance, we have allowed an interval of 3 months to elapse before this retest is requested.