ORIGINAL ARTICLE Volatile Organic Compounds in Exhaled Air as Novel Marker for Disease Activity in Crohn’s Disease: A Metabolomic Approach Alexander G. L. Bodelier, MD,* ,† Agnieszka Smolinska, PhD, ‡ ,§ Agnieszka Baranska, MSc, ‡ ,§ Jan W. Dallinga, PhD, ‡ Zlatan Mujagic, MD,* Kimberly Vanhees, PhD, ‡ Tim van den Heuvel, MSc, † Ad A. M. Masclee, PhD, † Daisy Jonkers, PhD, † Marie J. Pierik, PhD, † and Frederik J. van Schooten, PhD ‡ Background: Disappearance of macroscopic mucosal inflammation predicts long-term outcome in Crohn’s disease (CD). It can be assessed by ileocolonoscopy, which is, however, an invasive and expensive procedure. Disease activity indices do not correlate well with endoscopic activity and noninvasive markers have a low sensitivity in subgroups of patients. Volatile organic compounds (VOCs) in breath are of increasing interest as noninvasive markers. The aim of this study was to investigate whether VOCs can accurately differentiate between active CD and remission. Methods: Patients participated in a 1-year follow-up study and Harvey–Bradshaw index, blood, fecal, and breath samples were collected at regular intervals. Patients were stratified into 2 groups: active (fecal calprotectin .250 mg/g) or inactive (Harvey–Bradshaw index ,4, C-reactive protein ,5 mg/L, and fecal calprotectin ,100 mg/g) disease. Breath samples were analyzed by gas chromatography–time-of-flight mass spectrometry. Random forest analyses were used to find the most discriminatory VOCs. Results: Eight hundred thirty-five breath-o-grams were measured, 140 samples were assigned as active, 135 as inactive disease, and 110 samples of healthy controls. A set of 10 discriminatory VOCs correctly predicted active CD in 81.5% and remission in 86.4% (sensitivity 0.81, specificity 0.80, AUC 0.80). These VOCs were combined into a single disease activity score that classified disease activity in more than 60% of the previously undetermined individuals. Conclusions: We showed that VOCs can separate healthy controls and patients with active CD and CD in remission in a real-life cohort. Analysis of exhaled air is an interesting new noninvasive application for monitoring mucosal inflammation in inflammatory bowel disease. (Inflamm Bowel Dis 2015;21:1776–1785) Key Words: noninvasive marker, breath test, IBD C rohn’s disease (CD) is a chronic relapsing inflammatory dis- ease of the gastrointestinal tract and with ulcerative colitis (UC) referred to as inflammatory bowel disease (IBD). 1 Chronic mucosal inflammation in CD will eventually lead to irreversible bowel damage with complications like strictures or fistula. Adequate monitoring of (sub)clinical mucosal inflammation is therefore of major importance in optimizing therapeutic strategies and prevent- ing complications. Ileocolonoscopy remains the gold standard for assessment of macroscopic mucosal inflammation but is an expen- sive and invasive procedure. Disease activity indices (e.g., Crohn’s Disease Activity Index) have been developed for systematic eval- uation of the outcome in clinical trials. 2 However, the indices are cumbersome in clinical practice and potentially overlap with symptoms of irritable bowel syndrome or noninflammatory stric- tures. Furthermore, recent studies show that Crohn’s Disease Activity Index is not a reliable predictor of endoscopic disease activity. 3,4 Several noninvasive biomarkers are used in clinical practice, measuring an increased concentration of proteins in serum and stool. 5 C-reactive protein (CRP) and erythrocyte sedimentation rate reflect systemic inflammation and are not specific for CD. Further- more, CRP and erythrocyte sedimentation rate response are not found in all patients with IBD with active inflammation. 6–9 Fecal calprotectin (FC) shows good diagnostic precision in distinguishing IBD from healthy controls. 10 FC seems a reliable predictor of relapse in IBD and correlates significantly with endo- scopic disease activity. 11–14 Although FC is a sensitive marker for colonic inflammation, it is not a specific marker for IBD because elevated levels are also found in patients with infections, neoplasia, or after use of nonsteroidal anti-inflammatory drugs. 13 FC is prob- ably less sensitive for inflammation of the proximal colon or small Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.ibdjournal.org). Received for publication February 5, 2015; Accepted March 10, 2015. From the *Department of Gastroenterology and Hepatology, Maastricht University Medical Center+, Maastricht, the Netherlands; † Department of Gastroenterology, Amphia Hospital, Breda, the Netherlands; ‡ Department of Toxicology, Research Insti- tute NUTRIM, Maastricht University Medical Center+, Maastricht, the Netherlands; and § Top Institute Food and Nutrition, Wageningen, the Netherlands. A. G. L. Bodelier and A. Smolinska shared first authorship, and M. J. Pierik and F. J. van Schooten shared last authorship. Supported by grants from the Maag Lever Darm Stichting (Dutch Digestive Foundation) and Top Institute Food and Nutrition (TIFN GH001). The authors have no conflicts of interest to disclose. Reprints: Frederik J. van Schooten, PhD, Department of Toxicology, Research Institute NUTRIM, Maastricht University Medical Center+, Maastricht, the Netherlands (e-mail: f.vanschooten@maastrichtuniversity.nl). Copyright © 2015 Crohn’s & Colitis Foundation of America, Inc. DOI 10.1097/MIB.0000000000000436 Published online 8 May 2015. 1776 | www.ibdjournal.org Inflamm Bowel Dis  Volume 21, Number 8, August 2015 Copyright © 2015 Crohn’s & Colitis Foundation of America, Inc. Unauthorized reproduction of this article is prohibited.