Meta-analysis of dietary restriction during fecal occult blood testing

Dietary restriction is often recommended during fecal occult blood testing (FOBT) as a means of increasing test accuracy, but concern surrounds whether such restriction also reduces the chance that patients will complete the test.

We conducted a systematic review and meta-analysis to determine if advice about dietary restrictions affects the rate of completion of FOBT and the rate of positive results.

We searched the MEDLINE database and hand-searched the bibliographies of other systematic reviews and clinical practice guidelines to identify randomized trials of advice to perform dietary restriction during FOBT. We included only trials that reported the proportion of patients who completed the occult blood tests (completion rate). When such information was available, we also recorded the proportion of patients who had positive test results (positivity rate).

Five randomized trials met our inclusion criteria. All used guaiac-based Hemoccult tests; none reported results from rehydrated test slides. In four trials, there was little or no difference in test completion between patients assigned to dietary restriction and those with no restriction. In one small trial that used an especially restrictive diet, completion was 21 percentage points lower in the restricted group. Positivity rates were reported in four trials, none of which found a statistically significant difference between groups. Meta-analysis showed no difference in the summary positivity rate between those assigned to dietary restriction versus those not restricted (difference in positivity rate, 0%; 95% CI, -1% to 1%).

Available data suggest that advice to perform modest dietary restriction during unrehydrated FOBT does not affect the completion rate, but more severe restrictions may. Dietary restriction also does not appear to affect positivity rates. On the basis of these data, physicians do not need to advise patients to restrict their diet for nonrehydrated FOBTs.