The available clinical measures of Crohn's disease activity can be overly influenced by functional symptoms. Placebo response rates in clinical trials are high. Several non-invasive biomarkers are currently available for assessing inflammatory bowel disease (IBD) disease activity including erythrocyte sedimentation rate, C-reactive protein and fecal calprotectin. Although these markers hold some promise, their performance is less than ideal. What is needed is a simple, non-invasive, biologic measure of Crohn's disease.