Defining Normal Plasma Citrulline in Intestinal Transplant Recipients

Biopsy is the only means to identify intestinal graft rejection. Plasma citrulline (P-Cit) has been proposed as a marker for rejection after intestinal transplant (IT), but normative data is lacking. We analyzed P-Cit in IT recipients without rejection or other histological abnormalities. In 40 patients, P-Cit was measured with a Beckman amino acid analyzer within 24 h of protocol or clinically indicated endoscopic biopsy procured > 6 and < 360 days post-IT. Measurements included for analysis corresponded to normal (or minimally abnormal) biopsies that remained so for 7 days. These criteria were met by 145 samples from 10 adults and 14 children. Overall mean P-Cit (nmol/mL) was 34.0 ± 19.9. Mean P-Cit was 22.2 ± 13.2 between 6 and 30 days post-IT, 34.9 ± 17.2 (p = 0.001) between 30 and 60 days, 43.6 ± 15.8 between 60 and 90 days (p = 0.001), then stable until the end of the first year. Plasma citrulline was lower in 13 patients with body surface area (BSA) ≤ 1 m² vs. 11 patients with BSA ≥ 1.1 m² (p = 0.0001). Plasma citrulline increased linearly during the first 120 days in both BSA groups (r = 0.573 and r = 0.512; p = 0.0001). Within 3 months after IT, variations in P-Cit based on body size and postop interval should be considered when evaluating the need for histological confirmation of graft dysfunction.