Point-of-Care Test Nearly Identical to ELISA at Detecting ADAs to Biosimilar Infliximab, SB2

A recent study of a rapid point-of-care (POC) test shows that it is virtually identical at detecting antidrug antibodies (ADAs) to a biosimilar infliximab, SB2 (Renflexis, Flixabi), as a standard enzyme-linked immunosorbent assay (ELISA) and is suitable for therapeutic drug monitoring of any infliximab product.

The test is the only rapid test available for POC testing of ADAs to infliximab. It is based on lateral flow (LF) technology to detect free antibodies to infliximab in whole blood (capillary or venous), serum, or plasma.

Called the Promonitor Quick ANTI-IFX POC LF, the assay was previously shown to detect antibodies to both reference infliximab (Remicade) and to biosimilar CT-P13 (Inflectra, Remsima), and antibodies were shown to be equivalent in capillary blood taken from a finger prick as well as regular serum collected by venipuncture for therapeutic drug monitoring (TDM).

But detection of antibodies to Flixabi had previously only been proved by ELISA; data using LF technology were lacking.

Researchers compared the performance of the POC LF test with the standard ELISA technique for TDM in patients with inflammatory bowel disease who were treated with SB2.

In total, 202 trough sera were collected at a German hospital for analysis, and these sera corresponded to 76 patients with IBD (46 had Crohn disease, 26 had ulcerative colitis, and 4 had indeterminate colitis) treated with SB2 only. Samples were frozen for subsequent testing with ELISA and with the POC test.

The LF test uses the same format as the bridging ELISA. The POC test (limit of detection [LoD] = 23 AU/ml) results were read visually at 30 minutes after adding 15 µl of serum. ELISA (LoD=5 AU/ml) quantitative results were categorized as positive or negative to allow comparisons with the POC test.

The rapid test correctly detected anti-infliximab antibodies to SB2 and showed an almost perfect agreement with the reference ELISA method: 124 out of 202 samples tested positive for anti-SB2 antibodies with the POC test, while 144 samples tested positive with the ELISA.

Positive and negative agreements between ELISA and the POC test were 86.1% and 100%, respectively. Fourteen (70%) out of the 20 discrepancies found were due to anti-SB2 antibody concentration below the LoD of the POC test. Positive and negative agreements were 95.4% and 100%, respectively (124 LF-positive and 130 ELISA-positive sera) within common measurement ranges.

The remaining 6 discrepancies (positive with ELISA and negative with LF) corresponded to samples of 2 patients who were confirmed as true positives by radioimmunoassay.

Reference

Atreya R, Schmitt H, Fischer S, et al. Point of Care detection of anti-infliximab antibodies in inflammatory bowel disease patients treated with the biosimilar SB2: Performance comparison with ELISA. Presented at: 14th Congress of the European Crohn’s and Colitis Organisation; March 6-9, 2019; Copenhagen, Denmark. Abstract P554.