OBJECTIVES: Infliximab is an antitumour necrosis factor agent used to treat inflammatory bowel disease (IBD). Measurement of infliximab trough concentrations (C-troughs) are used to optimize drug exposure and improve outcomes. Currently, enzyme-linked immunosorbent assays (ELISAs) are used predominantly for this purpose. Novel lateral flow immunoassays provide a rapid result. METHODS: We collected 100 paired serum samples of adolescents and young adults with IBD, who were treated with infliximab maintenance infusions. C-troughs were measured with the Quantum Blue(R) lateral flow test (QB) with ELISA. Results were categorized as low-range (mean C-trough </=5 microg/mL) or high-range (>5 microg/mL). A Bland-Altman plot was created with limits of clinical acceptability set at </=2 microg/mL for low-range and </=40% for high-range C-troughs. A concordance matrix was created to evaluate the C-trough-based clinical scenario (whether or not to escalate infliximab) using a cutoff value of 5 microg/mL. RESULTS: Agreement between QB and ELISA was good (intraclass correlation coefficient: 0.85). In the low-range, 90% (95% confidence interval [CI]: 79-96) of measurements were within the limits of clinical acceptability. In the high-range this was 67% (95% CI: 53-79). QB provided higher results than ELISA. The concordance matrix showed 81% agreement (95% CI: 72-88, kappa: 0.62). CONCLUSIONS: Lateral flow- and ELISA-based infliximab C-trough measurements were in agreement. The swift establishment of infliximab C-troughs matters for patients experiencing increased disease activity. In the event of a low C-trough, prompt dose escalation can be initiated.