Background:Mucosal healing is presently considered one of the primary goals in treatment of Crohn's disease (CD), but this can only be confirmed by endoscopy. We aimed to design and validate a new disease activity index based on a combination of clinical characteristics and readily available laboratory parameters, which reliably predicts the presence and severity of endoscopic disease activity in patients with CD.Methods:Thirteen clinical characteristics and laboratory variables were selected for analysis. Endoscopic disease activity was assessed by the Crohn's disease Endoscopic Index of Severity. A linear regression model was based on 93 ileocolonoscopies performed in 82 patients with CD and internally validated by bootstrap resampling. Subsequently, the newly developed model was validated in a cohort of 99 patients.Results:The number of liquid stools during 1 day x 0.25 + C-reactive protein (in milligrams per liter) x 0.1 + platelet count (x10(9)/L) x 0.01 + fecal calprotectin (in milligrams per liter) x 0.001 - mean platelet volume (in femtoliters) x 0.2 optimally predicted the severity of endoscopic disease activity (bootstrap adjusted R-2 = 0.50). The model demonstrated good agreement in the external validation (r = 0.7), especially for (ileo)colonic CD (r = 0.8). Using receiver operator characteristic statistics, a cutoff point of 3 on the new index indicated endoscopic disease activity with a sensitivity of 80% and a specificity of 92%.Conclusions:This newly developed, noninvasive, index was found to reliably predict endoscopic disease activity in patients with CD. This tool can facilitate clinical decision making and might prove valuable in clinical trials.