Citrulline as a marker of intestinal function and absorption in clinical settings: A systematic review and meta‐analysis

Background Citrulline has been described as a marker of intestinal function or absorption but evidence varies according to clinical settings. Objective The objective of this article is to examine the evidence of plasma citrulline as a marker of intestinal function and absorption in various clinical settings. Methods Studies were examined for p values, means and standard deviations, correlation coefficients or other metrics depicting the association of citrulline with intestinal function. A random effects model was used to produce a pooled estimate. A hierarchical summary receiver operating curve model was fitted for diagnostic accuracy measures. Results Citrulline levels are correlated strongly with small bowel length in short bowel syndrome patients ( r  = 0.67). Citrulline is strongly negatively correlated ( r  = –0.56) with intestinal disease severity with regards to enteropathies (coeliac disease, tropical enteropathy, Crohn’s disease, mucositis, acute rejection in intestinal transplantation). Citrulline cut‐off levels have an overall sensitivity and specificity of 80% and 84% respectively. Citrulline levels in untreated coeliac patients compared to controls were reduced by 10 µmol/l. Citrulline levels increase with gluten‐free diet and with improvement of enteropathy. Citrulline is decreased in critical illness and sepsis. Conclusion These findings allow us to advocate quite reasonably that citrulline is a marker of acute and chronic intestinal insufficiency.