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P508. Evaluation of the diagnostic performance of two commercially available tests for infliximab trough levels (IFX-TL) and antibodies to infliximab (ATI) titration in inflammatory bowel disease (IBD)

M. Daperno1, F. Frigerio1, C. Guiotto2, L. Germano2, E. Ercole1, S. Aricò1, M. Fracchia1, C. Rigazio1, A. Lavagna1, R. Pellerito3, M. Migliardi2, R. Rocca1, 1AO Ordine Mauriziano, Gastroenterology Unit, Torino, Italy, 2AO Ordine Mauriziano, Laboratory Unit, Torino, Italy, 3AO Ordine Mauriziano, Rheumatology Unit, Torino, Italy

Background

Infliximab and adalimumab are approved and widely used for the treatment of Crohn's disease (CD) and ulcerative colitis (UC) refractory or intolerant to conventional treatments.

Recently it has been shown that higher drug trough levels are associated to better disease outcomes, and presence of elevated ATI is associated to poor outcomes and probability of adverse events.

Based on such observations, therapeutic algorithms based on drug monitoring (IFX-TL) combined with anti-drug antibodies detection (ATI) were proposed.

Nonetheless the comparative diagnostic performance of different commercially available diagnostic tests is not known.

Methods

A consecutive series of inflammatory bowel disease (IBD) outpatients, undergoing regular infliximab i.v. dosing, was prospectively enrolled. All cases underwent a blood sampling before planned infliximab infusion. Detailed clinical history was collected. Sera were stocked untill analyses were carried out. Two different ELISA-sandwitch tests were used according to manufacturers' suggestions in order to determine IFX-TL and ATI concentrations: Promonitor® IFX Determination of Drug and Anti-drug Antibodies Concentration (Menarini, Italy) and TNF Blocker Monitoring e Antibodies against TNF Blocker kits (ImmunDiagnostik, Bensheim, Germany).

Results

66 IBD patients (39 CD and 27 UC, respectively; and 20 with active disease and 46 with quiescent disease, respectively, 39 males and 27 females), and 12 SpA-CTRLs were recruited.

Correlation of the 2 diagnostic tests was good for IFX TL dosing: Spearman's rho 0.913 (95% CI 0.859–0.946), p < 0.0001; median TL were 2.9 µg/ml (range 0.0–32.0) and 4.4 µg/ml (range 0.0–34.5) for Promonitor and ImmunDiagnostik test, respectively. For ATI detection (6/63 cases, 9.5%), both tests showed identical results.

Coefficient of variation from Promonitor and ImmunoDiagnostik IFX-TL tests was 56.65%, from ATI tests was 979.35%.

IFX-TL tests correlated well with each other, Bland–Altman plots confirms this result (Figure 1).

Figure 1. Bland–Altman plot comparing Promonitor and Immuno­Diagnostik tests confirms good correlation between methods.

Conclusion

Preliminar results of this single-center study seem to support similar performance for the two different tests evaluated. Data on a larger cohort of patients and controls are needed to support these preliminar results.