677 Outcomes of Infliximab Treated IBD Patients Undergoing Simultaneous Therapeutic Drug Monitoring With Two Different Assays

Abstract

INTRODUCTION: There are multiple assays for infliximab (IFX) trough level (IFX-TL) and antibody (ATI) measurement. The aims of this study are to examine the correlation and outcomes of IFX-TL and ATI measured with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and electrochemiluminescence (ECLIA) in inflammatory bowel disease (IBD) patients. METHODS: This was a prospective study of IFX-treated IBD patients undergoing drug monitoring with an ECLIA panel (Esoterix Laboratories). Residual serum samples were used to simultaneously quantify IFX-TL via LC-MS/MS and ATI via an in-house ECLIA (iECLIA) (Mayo Clinic). Both LC-MS/MS and iECLIA have been previously validated. Primary outcomes: IFX-TL and ATI comparison between the two assays. Secondary outcomes: association of IFX-TL and ATI with clinical remission, mucosal healing (MH) (absence of ulcers in Crohn's disease and Mayo endoscopic score ≤1 for ulcerative colitis) and normal serum C-reactive protein (CRP ≤8 mg/L). RESULTS: A total of 151 patients were included (median age 32 years (12-84), 45.7% female) (Table 1). Median IFX-TL was 7 mcg/mL (IQR: 1.3, 19.4) and 6 mcg/mL (IQR: 0.9, 20) via LC-MS/MS and ECLIA, respectively (Spearman correlation coefficient r = 0.975). Median IFX-TL via LC-MS/MS was not significantly different between patients in clinical remission, response and no response (5.7 vs. 8.4 vs. 2.3 mcg/mL, respectively; P = 0.46), but significantly higher in patients who had a normal CRP (11.1 vs. 1.4 mcg/mL; P < 0.001) and in those who achieved MH (13.1 mcg/mL vs. 3.9 mcg/mL; P = 0.01). ATI was detected in 13/142 (9.2%) via iECLIA and 39/151 (25.8%) via ECLIA. The frequency of ATI detection via iECLIA was lower in patients in clinical remission or response than no response (7.3% vs. 9.3% vs. 15.4%; P = 0.68). On the contrary, the frequency of ATI detection via ECLIA was higher in patients with clinical remission (35.7%) than response (18.7%) and comparable to patients who had no clinical response (40%) (P = 0.05) (Table 2). The frequency of ATI was not significantly different between patients who did and did not achieve MH or had normal CRP using both assays (Table 2). CONCLUSION: IFX-TL was comparable between LC-MS/MS and ECLIA assays. IFX-TL correlated with MH and normal CRP but not clinical remission. Frequency of ATI detection was not significantly associated with outcomes via both methods. ATI detected via iECLIA showed a trend towards correlation with clinical outcomes compared to ECLIA.