The relationship between fasting plasma citrulline concentration and small intestinal function in the critically ill

Alexis Poole, Adam Deane, Matthew Summers, Janice Fletcher, Marianne Chapman

IntroductionThis study aimed to evaluate whether fasting plasma citrulline concentration predicts subsequent glucose absorption in critically ill patients.MethodsIn a prospective observational study involving 15 healthy and 20 critically ill subjects, fasting plasma citrulline concentrations were assayed in blood samples immediately prior to the administration of a liquid test meal (1 kcal/ml; containing 3 g of 3-O-methyl glucose [3-OMG]) which was infused directly into the small intestine. Serum 3-OMG concentrations were measured over the subsequent four hours, with the area under the 3-OMG concentration curve (AUC) calculated as an index of glucose absorption.ResultsThe groups were well matched in terms of age, sex and BMI (Healthy vs Patients; mean [range] 47 [18¿88] vs 49 [21¿77] years; 60% vs 80% Male; BMI 25.2 [18.8-30.0] vs 25.5 [19.4-32.2] kg/m2). Compared to the healthy subjects, critically ill patients had reduced fasting citrulline concentrations (26.5 [13.9 - 43.0] vs. 15.2 [5.7 - 28.6] ¿mol/L; P¿<¿0.01) and glucose absorption (3-OMG AUC: 79.7 [28.6 - 117.8] vs 61.0 [4.5 - 97.1] mmol/L.240 min; P¿=¿0.05). There was no relationship between fasting citrulline concentrations and subsequent glucose absorption (r¿=¿0.28; P¿=¿0.12).ConclusionsWhile both plasma citrulline concentrations and glucose absorption were reduced in critical illness, fasting plasma citrulline concentrations were not predictive of subsequent glucose absorption. These data suggest that fasting citrulline concentrations do not appear to be a marker of small intestinal absorptive function in the critically ill.