Abstract Background Perianal fistulizing Crohn’s disease (CD) is more prevalent in males and children, with higher rates in Korean patients compared with Europeans. Research on infliximab (IFX) trough levels (TL) has mostly focused on adults. This study compared point-of-care testing (POCT) with proactive therapeutic drug monitoring (TDM) versus symptom-based dosing in pediatric patients with perianal fistulizing CD, evaluating radiologic fistula healing. Methods In this prospective study, pediatric patients (≤18 years) newly diagnosed with perianal fistulizing CD between January 2023 and July 2025 were randomized 1:1 to a proactive TDM group (n = 45) or a clinical group (n = 43). Outcomes after one year of IFX included magnetic resonance imaging (MRI)-based perianal healing, and further analyses explored the association between IFX TL and radiologic fistula healing. Results At one year, the TDM group showed significantly greater radiologic improvement, with lower MRI-based fistula scores compared with the clinical group. Mean IFX TLs were higher in the TDM group (12.78 µg/mL) versus the clinical group (4.96 µg/mL, p 0.001). Patients with healed fistulas had higher TLs at week 24–30 (9.28 µg/mL) compared with non-healed patients (6.30 µg/mL, p 0.001). Multivariate analysis identified IFX TL at week 24–30 as the independent predictor of radiologic healing (OR 1.14; 95% CI 0.02-0.24; p 0.05). Receiver operating characteristic (ROC) analysis showed an optimal cutoff of 6.95 µg/mL (AUC 0.65). Kaplan–Meier analysis confirmed significantly higher healing rates with TL ≥ 6.95 µg/mL by week 24–30. Conclusion Proactive POCT-guided therapy achieved superior one-year radiologic fistula healing compared with symptom-based care. The key determinant of perianal fistula healing was IFX TL at week 24-30 (6-month), with an optimal threshold of 6.95 µg/mL. Achieving TL ≥ 6.95 µg/mL within six months may enhance perianal fistula healing in pediatric CD. References: 1. Korean children and adolescents with Crohn’s disease are more likely to present with perianal fistulizing disease ant diagnosis compared to their european counterparts. B.Kang et al. Pediatr Gastroenterol Hepatol Nutr. 2020 Jan;23(1):49-62. doi: 10.5223/pghn.2020.23.1.49. Epub 2020 Jan 9 2. Higher infliximab trough levels are associated with perianal fistula healing in patients with Crohn’s disease. A J Yarur et al. Aliment Pharmacol Ther. 2017 Apr;45(7):933-940. doi: 10.1111/apt.13970. Epub 2017 Feb 17. 3. Association of Induction Infliximab Levels With Clinical Response in Perianal Crohn’s Disease. Yana Davidov et al. J Crohns Colitis. 2017 May 1;11(5):549-555. doi: 10.1093/ecco-jcc/jjw182. 4. Higher Anti-tumor Necrosis Factor-α Levels Correlate With Improved Radiologic Outcomes in Crohn’s Perianal Fistulas. Michael De Gregorio et al. Clin Gastroenterol Hepatol. 2022 Jun;20(6):1306-1314. Conflict of interest: Prof. Kim, Yoon Zi: No conflict of interest Kwon, Yiyoung: No conflict of interest Jeong, Tae Jong: No conflict of interest Kim, Seon Young: No conflict of interest Kim, Hansol: No conflict of interest Kim, Eun Sil: No conflict of interest Choe, Yon Ho: No conflict of interest Kim, Mi Jin: No conflict of interest
Kim et al. (Thu,) studied this question.