HOW LONG TO ABSTAIN FROM EATING RED MEAT BEFORE FECAL OCCULT BLOOD-TESTS

Although previous reports have documented that red meat can cause false-positive fecal occult blood tests, the duration of this effect has not been reported. In this study, 46 healthy young men and women (mean age, 25.6 years) ingested 350 to 450 g/d of red meat for 3 days followed by a diet containing no red meat for 7 more days (days 1 to 7). While abstaining from red meat, consecutive stool samples were obtained and assayed for four fecal blood tests: Hemoccult, Hemoccult SENSA, HemoQuant, and HemeSelect. The false-positive rate for Hemoccult was 15.4%, 5.5%, 5.5% for days 1 to 3 and 0% thereafter; for Hemoccult SENSA, 46.2%, 41.6%, 8.3%, and 0% for days 1 to 4; and for HemoQuant, 31.6%, 28.5%, 14.2% 5.6%, and 0% for days 1 to 5. HemeSelect had no false-positive results on any day. The data suggest that the abstention period from red meat before fecal occult blood testing should be at least 3 days for Hemoccult and Hemoccult SENSA and 4 days for HemoQuant. This may reduce the false positivity and increase the positive predictive value of these tests. Further, HemeSelect may have better specificity than the other fecal occult blood tests.