Purpose of review: Irritable bowel syndrome (IBS) is among the most commonly encountered conditions in primary care and gastroenterology. There is ample evidence that an IBS diagnosis based on symptom-based criteria and exclusion of alarm features that would otherwise support diagnostic testing is accurate and durable. For many clinicians, however, IBS remains a diagnosis of exclusion because of concern surrounding missed diagnoses of inflammatory bowel disease (IBD) or other organic gastrointestinal diseases. Using blood and/or fecal biomarker tests to shift the precolonoscopy probability of IBD in patients with symptoms mimicking IBS is becoming an increasingly reasonable practice with improvement in 'preliminary' tests.
Recent findings: Fecal calprotectin (FCP) testing appears to be the most sensitive preliminary test for discriminating IBD from IBS. Although both fecal lactoferrin and FCP were superior to serum C-reactive peptide (CRP) in their diagnostic accuracy, FCP is superior to fecal lactoferrin based on available literature.
Summary: In patients with IBS with diarrhea who have not undergone previous extensive evaluation, the ability of screening tests to detect colonic inflammation is improving. FCP and fecal lactoferrin are reliable predictors of colonic inflammation and should be considered for standard testing in patients with IBS-D symptoms to help identify those who would benefit most from colonoscopy. Although predictive, there currently are no fecal or serum tests that can definitively identify or subtype IBD.