BACKGROUND Monitoring of trough levels and anti-drug antibodies is important when patients with inflammatory bowel disease (IBD) are treated with anti-TNF biologics due to guided therapeutic decisions. The comparability of 3 ELISA tests for detection of the lowest serum concentration of infliximab (IFX) or antibodies to IFX (ATIs) was evaluated. MATERIAL AND METHODS Two commercial assays for measuring IFX levels were compared with the in-house (UHL) test. ATIs were measured with 1 commercial test and compared to the in-house test. According to the guidelines, IFX levels were within the range of 3 to 7 µg/mL. RESULTS The decision to continue therapy would be the same for 11 out of 16 patients when comparing the apDia Infliximab ELISA and UHL test, and for 12 out of 18 patients when comparing the Lisa-Tracker and in-house UHL test. Linear correlations between the tests were R=0.92 (UHL and apDia), R=0.91 (apDia and Lisa-Tracker), and R=0.89 (UHL and Lisa-Tracker) with P<0.001, respectively. CONCLUSIONS As the IFX levels are important for decisions on further therapy, detectable IFX levels realistically reflect the presence of the drug in the patients' blood and thus control inflammatory activity. The tests were found as comparable and performed well in this aspect and might be used in everyday clinical practice.