Plasma Citrulline as a Biomarker in Critical Illness: A Structured Narrative Review

Introduction

Gastrointestinal dysfunction is common in critically ill patients and is associated with increased morbidity and mortality. Plasma citrulline, a non-proteinogenic amino acid synthesized by enterocytes, has been proposed as a biomarker of intestinal function and enterocyte mass. However, the available evidence regarding its clinical significance in critically ill patients remains heterogeneous. This structured narrative review aimed to evaluate the current evidence on plasma citrulline in critical illness, focusing on its association with gastrointestinal dysfunction, disease severity, and clinical outcomes.