Plasma Citrulline Level: A Simple, Sensitive Method to Assess and Monitor Small Bowel Absorptive Function in Patients With Crohn's Disease?

Preliminary studies reported that plasma citrulline concentrations may be a reliable biochemical marker for intestinal dysfunction and absorptive enterocyte mass. The relationship between citrulline concentration and intestinal function has been supported in other studies including those examining rejection in small bowel allografts. Concentrations of citrulline are dramatically reduced in cases of mucosal damage (e.g. moderate graft rejection or viral enteritis) and strongly correlate (inversely) with severity on biopsy. Plasma citrulline concentration is lower also in patients with villous atrophy (24±13 μmol/L) than in healthy subjects (40±10 μmol/L) and patients with anorexia nervosa (39±9).

A citrulline threshold of 20 µmol/L apparently permitted the classification of short bowel syndrome patients into either transient or permanent intestinal failure categories, with 92% sensitivity, 90% specificity, and 95% positive and 86% negative predictive values, respectively. Experimental studies have been carried out also in assessing the value of citrulline as a marker for severity of small bowel epithelial damage from radiation. The plasma citrulline was shown to be a simple, non-invasive and sensitive assay to monitor and quantify radiation-induced small bowel damage in mice and humans. Otherwise, the literature on citrulline as a potential marker of intestinal and nutritional integrity is young and data for specific conditions come only from single centres; there are limited data on normal ranges. More crucially, however, there has been no attempt to clarify the effect of inflammation on citrulline homeostasis. To date there is no information in respect of patients with intestinal failure in whom there has been no resection.

We hypothesise that plasma citrulline concentration reflects small bowel absorptive capacity and correlates to the functional intestinal length independently from inflammation.

Comparisons: To exclude the possibility that citrulline merely reflects inflammation, control groups (six subjects each) with short bowel syndrome without inflammation (mesenteric infarct) (negative control); and those with inflammation but no anatomical loss (active coeliac disease) (positive controls); will be studied as well as healthy volunteers.

The study is designed to utilise patients from the positive and negative control groups to permit a correlation of plasma citrulline with intestinal length and with a "gold standard" assessment of intestinal function as judged from the patients need for nutritional intervention (from normal diet to dependence on home parenteral nutrition).