Introduction The purpose the aim to examine the evidence of citrulline plasma of citrulline as a marker of intestinal functions and absorption in clinical conditions.
Method The inclusion criteria for this systematic review were: any empirical study (abstract and full paper) describing investigation of citrulline in relation to the term intestinal function. PRISMA guidelines and MOOSE checklist for systematic reviews and meta-analyses were used. Electronic database searches were conducted up until 1 July 2015. Studies were examined for p-values, means and standard deviations, correlation coefficients or other metrics depicting the association of citrulline with intestinal function. Metrics were converted to the standardised mean difference (SMD) 1, 2 or weighted mean difference (WMD), where means and standard deviations for groups under comparison were identified 3; and/or correlation coefficients (CCs). A random effects model was used to produce a pooled estimate of the SMDs/WMDs/CCs. Regarding diagnostic accuracy data, following the robust construction of the diagnostic 2×2 tables, specificity, sensitivity, and 95% CI for each of the included studies was calculated. A hierarchical summary receiver operating curve (HSROC) model was fitted to provide a summary receiver operating curve and to allow derivation of pooled sensitivity and specificity estimates.
Results Citrulline levels are correlated strongly with small bowel length in short bowel syndrome patients (correlation coefficient over 0.500). Citrulline is strongly negatively correlated (correlation coefficient over 0.500) with intestinal disease severity with regards to enteropathies (coeliac disease, tropical enteropathy, Crohn’s disease, mucositis, and acute rejection in intestinal transplantation). Citrulline cut off levels have an overall sensitivity and specificity of 80%. There was however variability in the cut-off levels, but the majority of studies used cut-off level of 20 μmol/L. 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. The existing literature indicates that it could possibly be attributed to use of nitric oxide and arginine in sepsis/inflammation leading to a transient decrease in citrulline; similar to the behaviour of albumin as a negative inflammatory marker. Secondly, it could also indicate enteropathy of acute illness.
Conclusion These findings allow us to advocate quite reasonably that citrulline is a marker of possible acute intestinal injury.
Disclosure of Interest None Declared
- Intestinal failure
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