Monitoring the concentration of TNF antagonist drugs and detecting the development of anti-drug antibodies (ADA) enables physicians to optimize patient treatment over time. The test results help physicians understand underlying causes of suboptimal outcomes, make informed therapy choices, and provide more effective treatment to their patients. The use of TNF antagonist has revolutionized the treatment of patients with several non-infectious inflammatory disorders, including Crohn disease and ulcerative colitis.

There are different approaches to manage patients with treatment failure to TNF antagonists; one approach is to monitor drug levels and anti-drug antibodies. A new guideline from the American Gastroenterological Association on therapeutic drug monitoring in inflammatory bowel disease recommends that physicians should perform reactive therapeutic drug monitoring to guide changes in TNF antagonist therapy.

Current methods for ADA detection are complicated by the fact that most TNF antagonist are antibodies and by the complexity of measuring antibodies against antibodies in non-functional binding assays. More importantly, all non-ARUP methods fail to differentiate binding from neutralizing ADA.

ARUP’s TNF antagonist activity and neutralizing antibody assays are cell-based bioassays that measure the ability of a drug to inhibit TNF. The assays also detect the presence of antibodies that neutralize drug activity. Emergence of these neutralizing antibodies in a patient leads to treatment failure. Other methods detect anti-drug antibodies that bind to the drug, but unlike ARUP’s assays, these methods are not able to distinguish whether the antibodies neutralize drug activity or not.

Test Information

How ARUP’s Test Works

  • TNF antagonist activity and its inhibition by TNF antagonists 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 TNF antagonists), and 1:20 dilution (for anti-drug antibodies). Values below these cutoffs will be reported as "Not Detected."

This functional reporter gene assay uses the principles of iLite technology (licensed by Euro Diagnostica).

Reporter cells carry a TNF inducible, NFκB-regulated firefly luciferase reporter-gene construct. When TNF is added to the cells, the reporter gene turns on and generates firefly luciferase, which is measured by a luminometer. Results of firefly luciferase expression are normalized relative to the expression of the renilla luciferase gene, which is carried by the same reporter cell and under the control of a constitutive promoter.

Drug Measurement

Serum of a patient taking a TNF antagonist drug is mixed with TNF and added to the cells. If the drug is present, it will block the activity of TNF, decreasing luminescence. Serum concentration of biologically active TNF drug can be calculated using a calibration curve.

Antibody Development

Some patients develop antibodies to the drug. In the presence of neutralizing antibodies, the reporter gene is turned on despite the presence of exogenous drug in the assay. The antibody titer is obtained by identifying the dilution point of a patient’s serum where blocking of the drug activity is no longer observed.

The functional reporter gene assays were clinically validated for diagnosing and monitoring TNF antagonist treatment failure.

Currently, the ARUP assays are the only clinical assays available for the detection of biologically active TNF drugs and ADA with drug-neutralizing function, as recommended by the FDA.

The ARUP cell-based assay is inherently more reflective of the in vivo situation in tissue and circulation, under which TNF antagonists drugs are believed to function, and can easily be adapted for all known anti-TNF drugs.

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)
ELISA
(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  
Yes
 
No
 
No
 
No
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

FAQ

How does ARUP's Infliximab test compare with other tests?

  • The main difference is that ARUP's test measures bioactivity of the drug and of the neutralizing antibody. See table below for comparison of methods to monitor anti-drug antibody (ADA) levels in serum.
    ARUP Infliximab/Adalimumab Assay
      ARUP assy (reporter gene assay) ELISA (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 Yes No No No
    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

What is the precision of measurements of drug and drug-neutralizing antibody in this test?

  • Based on ARUP's internal validation data, the CVs are less than 20% for both the drug and the drug-neutralizing antibody measurements.

The instruction says to test the patient before infliximab or adalimumab treatment. Why? How soon can the test be done after the last infusion?

  • The most effective timing for the test is just prior to the next treatment when the drug level is lowest in the patient (at trough). This is the time when information about drug metabolism can best be determined. Accurate levels of anti-drug antibody (ADA) cannot be measured if the patient is tested immediately after infliximab treatment. The overwhelming amount of drug will absorb the ADAs and will interfere with its detection. This is true with all tests regardless of the methodology used. The minimum amount of time required after the last infusion for testing will depend on the pharmacokinectics and pharmacodynamics of the drug in each patient. In general, it should be at least 72 hours after treatment and we strongly encourage testing right before the next treatment. The bioactivity measurements of the iLite assay used in ARUP's test has a lower possibility of false negative results for ADA measurements compared to traditional methods using solid phase ELISA.

Additional Resources

Enhanced Reports

References