Infliximab Activity & Neutralizing Antibody

This test is used to aid in the evaluation of response failure to infliximab (Remicade). Serum levels of infliximab and anti-infliximab antibodies are reported based on the bioactivity of the drug, i.e. its ability to inhibit tumor necrosis factor alpha (TNF-α). The test uses the principles of iLite™ technology (see details under "How it works"). At this time, this is the only clinical assay available for detecting biologically active infliximab in serum.

Infliximab is used for the treatment of patients with chronic inflammatory diseases such as rheumatoid arthritis, Crohn’s disease, ulcerative colitis, and psoriasis. Unfortunately, many patients receiving the recommended dose have inadequate responses, or experience secondary response failure. This necessitates intensified therapy or change to alternative treatments. Rise of anti-infliximab antibodies is seen in about 40–50% of patients treated with this drug. Recent studies on Crohn’s patients showed that the strategy using test results for infliximab and anti-infliximab antibodies is more cost effective than empiric dose escalation for managing patients who lost responsiveness to infliximab.

Features and Benefits

  • Aids in rational therapeutic decision for patients on TNF-blocking therapy
  • Test measures bioactivity using reporter cells
  • Recommended CPT code 86352 x 2
  • Interfaced reports
How it works
  • TNF-α activity and its inhibition by infliximab are measured by stimulation of cells carrying a TNF-responding luciferase gene, and quantifying luciferase expression by luminometry. The assay uses the principles of iLite™ technology (reference).
  • View the method brochure (download)
  • The following cutoff values are used: 0.65 ug/mL (for infliximab), and 1:20 dilution (for anti-infliximab antibody). Values below these cutoffs will be reported as "Not Detected".
How it compares with other tests

Methods to monitor anti-drug antibody (ADA) levels in serum

The main difference is that ARUP's test measures bioactivity of the drug and of the neutralizing antibody.

  ARUP Infliximab assay
(reporter gene assay)
(solid-phase bridging)
Fluid-phase RIA Homogeneous mobility-shift assay (size exclusion HPLC)
What the test measures
Bioactivity Binding Binding Binding
in vivo relevance to the drug's capacity to inhibit TNF in patient High Low Moderate Moderate
Specifically detects ADAs with drug-neutralizing function  
Detection of IgG4 antibodies (major isotype of ADAs) Yes No Yes Yes
Possibility of false negative ADA due to drug in sample Low High Low Low
Possibility of false positives due to neoepitopes, nonspecific binding, rheumatoid factors, complement components Low High Low Low
ADA = anti-drug antibodies; ELISA= enzyme-linked immunosorbent assay; RIA = radioimmunoassay

Test Report Examples

See description of ARUP's report formats...
Clients will receive the Interfaced Report (or an equivalent report through ARUP S2K or Connect systems). Additionally, this test provides a graphical report with logitudinal data (see Enhanced Report example). Connect Account users can download the Enhanced Report in bulk (access and account set up). Alternatively, each Enhanced Report can be downloaded individually using ARUP's web portal by entering the username/password provided in all of our standard reports. See the Interfaced Report example for the location of the username/password.

Ordering Information

Test Name Infliximab Activity and Neutralizing Antibody
Test Code 2008320
Mnemonic IFX NAB
Method Cell culture / Stimulated cell function assay / Chemiluminescent immunoassay, quantitative and semi-quantitative
Specimen required 1 mL serum, collect before infliximab infusion