Citrulline is an amino acid which forms a key intermediate in the urea cycle. It is also produced as a by-product of the enzymatic production of nitric oxide from arginine and in the gastrointestinal tract from glutamine. Citrulline has been proposed as a marker of gastrointestinal dysfunction in critical illness due to the correlation between citrulline levels and enterocyte mass and function in chronic GI diseases. However, three studies conducted in critical care populations were unable to demonstrate a significant association between citrulline and gastrointestinal dysfunction.
References:
Fragkos KC, Forbes A. Citrulline as a marker of intestinal function and absorption in clinical settings: a systematic review and meta-analysis. United European Gastroenterol J 2018;6(2):181e91.
Poole A, Deane A, Summers M, Fletcher J, Chapman M. The relationship between fasting plasma citrulline concentration and small intestinal function in the critically ill. Crit Care 2015;19(1):16
Padar M, Starkopf J, Starkopf L, Forbes A, Hiesmayr M, Jakob SM, et al. Enteral nutrition and dynamics of citrulline and intestinal fatty acid-binding protein in adult ICU patients. Clin Nutr ESPEN 2021;45:322e32.
Reintam Blaser A, Padar M, Mandul M, Elke G, Engel C, Fischer K, et al. Development of the Gastrointestinal Dysfunction Score (GIDS) for critically ill patients – a prospective multicenter observational study (iSOFA study). Clin Nutr 2021 Aug;40(8):4932e40.