Citrulline is an amino acid produced in the intestine and in the liver, but the liver does not contribute significantly to circulating citrulline concentrations. The intestine is thus the only organ that normally releases significant amounts of citrulline into the blood. The investigators have designed a study looking at the value of measuring plasma citrulline concentration in patients with Crohn’s disease and short bowel or normal intestinal length. Measuring the plasma citrulline concentration in short bowel patients may help to distinguish between patients who need permanent parenteral feeding from patients with just transient intestinal dysfunction. It may also help the investigators in understanding the small bowel intestinal length remaining and the absorptive integrity. In patients with normal intestinal length and Crohn’s disease, it may be a reliable marker of small bowel damage and could be applied to establish therapeutic improvements. It has been demonstrated to strongly correlate (inversely) with severity on intestinal biopsies.