It is unknown to what extent at what expense flexible sigmoidoscopy and colonoscopy add to the diagnosis of irritable bowel syndrome (IBS). The aim of the study was to assess the incremental cost-effectiveness of endoscopic procedures in the workup for IBS.
Using the Bayes formula, we calculated the increase in diagnostic certainty for a consecutive number of tests. We also calculated the incremental cost-effectiveness ratio, which corresponds to the test costs divided by the increment in diagnostic certainty.
The diagnosis of IBS can be established with a relatively high probability of more than 80% relying on relatively inexpensive and noninvasive tests only. Flexible sigmoidoscopy or colonoscopy constitute the most costly portion of any workup for IBS, which amounts to 50% to 75% of the overall costs. Because of their high incremental cost-effectiveness ratio, endoscopic procedures should not be used at the beginning of the diagnostic workup. This outcome of the analysis remains largely unaffected within reasonable ranges of the sensitivity and specificity of various tests.
In the diagnosis of IBS, inexpensive, noninvasive tests should be used first to rule out other diagnoses. Despite their high incremental cost-effectiveness ratio, flexible sigmoidoscopy and colonoscopy are indicated when a serious organic disease is reasonably likely and needs to be ruled out.