OBJECTIVES: Our aim was to explore the diagnostic value of fasting citrulline concentrations to detect decreased intestinal energy absorption in patients with recently diagnosed celiac disease (CeD), refractory celiac disease (RCeD), and short bowel syndrome (SBS). Decreased intestinal energy absorption is regarded a marker of intestinal failure. METHODS: Fasting plasma citrulline concentrations were determined by high performance liquid chromatography (HPLC) in a prospective study of 30 consecutive adult patients (15 CeD, 9 RCeD, and 16 SBS) and 21 healthy subjects. Intestinal energy absorption capacity using bomb calorimetry was determined in all patients and healthy subjects and was regarded as the gold standard for intestinal energy absorption function. RESULTS: The mean fasting plasma citrulline concentration was lower in RCeD patients than in healthy subjects (28.5 ± 9.9 vs 38.1 ± 8.0 μmol/L, P < 0.05) and CeD patients (28.5 ± 9.9 vs 38.1 ± 6.4 μmol/L, P < 0.05), however, clearly within reference values. The mean intestinal energy absorption capcity was lower in SBS patients than in healthy subjects (64.3 ± 18.2 vs 90.3 ± 3.5%, P < 0.001), CeD patients (64.3 ± 18.2 vs 89.2 ± 3.4%, P < 0.001), and the RCeD group (64.3 ± 18.2 vs 82.3 ± 11.7%, P < 0.01). No relation was observed between fasting plasma citrulline concentration and intestinal energy absorption capacity (Pearson r = 0.09, P = 0.56). The area under the ROC curve for fasting plasma citrulline to detect decreased intestinal energy absorption capcity (i.e., < 85%) was 0.50. CONCLUSION: Fasting plasma citrulline concentrations have poor test characteristics for detection of decreased intestinal energy absorption capacity in patients with enterocyte damage.