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P242 Performance of the BÜHLMANN Quantum Blue® Infliximab point-of-care assay dedicated for therapeutic drug monitoring of serum infliximab trough levels

T. Schuster*, E. Keller, S. Kräuchi, F. Bantleon, J. Weber, M. Schneider

BÜHLMANN Laboratories AG, Schönenbuch, Switzerland

Background

A successful and cost effective infliximab (mAb to TNFa) therapy for patients, suffering, eg, from Crohn’s disease and ulcerative colitis is jeopardised, if the drug is not adjusted within an ideal therapeutic window. Rapid point-of-care (POC) testing allows an immediate determination of the trough level, which cannot be done by other currently used analytical methods, such as the ELISA format. Here, we present the analytical performance characteristics as part of the validation of the first infliximab POC, ie, the Quantum Blue® infliximab assay from BÜHLMANN.

Methods

The sandwich lateral flow immunoassay uses a TNFa coated label and a highly specific monoclonal antibody to detect infliximab in a diluted human serum sample. Quantitative read out of the test cassette (TC) is performed by the BÜHLMANN Quantum Blue® Reader after 15 minutes. Relevant testing was performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines. The linearity study included multiple levels (12–14) of a serial sample dilution. The inter-lot precision was performed with 8 samples within the measuring range (5 days, 2 runs per day in 2 replicates). Method comparison to level infliximab ELISA kit (M2920, Sanquin, The Netherlands) is based on 93 serum samples. Cross-reactivity of other TNFa blockers was tested up to 100 µg/mL. Potentially interfering substances were tested i.e. other TNFa blockers (10 µg/mL or 1.7 µg/mL), azathioprine (60 µmol/L) / 6-mercaptopurine (37 µmol/L), methotrexate (1 363 µmol/L), high-level TNFa (2.6 ng/mL), and rheumatoid factors (RF, 497.3 IU/mL).

Results

The BÜHLMANN Quantum Blue® infliximab assay exhibits a limit of blank of 0.10 μg/mL, a limit of detection of 0.15 μg/mL and a limit of quantification of 0.4 to 20 µg/mL. The assay has been tested to be linear in the range from 0.26 to 21.55 µg/mL, while obtaining recovery values between 83.5% and 113.3%. No high-dose hook effect was observed up to 1 000 µg/mL of infliximab. The total precision of the device was 22.7%, with a repeatability of 21.1%. The method comparison revealed a slope of 1.09 and a regression coefficient (r) of 0.94 (Passing–Bablok) suggesting that the new Quantum Blue® infliximab assay showed an excellent correlation compared with the well-established Sanquin ELISA. No other TNFa blocker was recognised, nor did they interfere with the determination of infliximab. In addition, no interference was observed with other immunosuppressive drugs, TNFa, RFs, nor abnormal serum samples.

Conclusion

The BÜHLMANN Quantum Blue® infliximab assay enables the quantitative determination of the infliximab trough level in serum with a time to result of only 15 minutes. Hence, it represents a valuable tool for the clinician to assess the drug level of the patient right before the next infusion.