Laboratory Testing for Monoclonal Antibody Therapeutics

Content Review: February 2024 Last Update:

Monoclonal antibody therapeutics are biologic drugs that have transformed the management of numerous conditions, including cancers, autoimmune diseases, and inflammatory disorders such as inflammatory bowel disease (IBD) and rheumatoid arthritis (RA).  These drugs include anti-tumor necrosis factor (anti-TNF) drugs (eg, adalimumab, infliximab), immune checkpoint inhibitors (eg, many programmed death-ligand 1 [PD-L1] inhibitors), and many others.

Laboratory testing is used for therapeutic drug monitoring (TDM), an important strategy for maximizing therapeutic effect and minimizing adverse effects when administering monoclonal antibody therapeutics (particularly anti-TNF therapeutics). Therapeutic drug monitoring allows for individualized dosing regimens based on a patient’s unique pharmacokinetic and pharmacodynamic profile, aids in avoiding unnecessary dose escalations or drug discontinuations, and may reduce treatment costs. , , , 

Quick Answers for Clinicians

When should samples be collected for monoclonal antibody drug concentration testing and antidrug antibody assays?

Drug concentration and antidrug antibody detection tests are most effective when performed on specimens collected at trough drug concentrations (immediately before the next scheduled drug dose). 

Do monoclonal antibody therapeutic monitoring tests work for biosimilar drugs?

Biosimilar drugs are clinically comparable to reference products, although they are not completely identical.  Because biosimilars and assay platforms differ, it is important to ensure that laboratory tests for monoclonal antibody therapeutics have been validated for all products of interest, including reference products and biosimilars. 

Do monoclonal antibody therapeutics interfere with laboratory tests?

In some cases (eg, lymphocyte cross-match testing for histocompatibility, protein electrophoresis, and transfusion medicine), monoclonal antibody drugs may interfere with laboratory tests.  Such interference can have potential adverse effects on clinical care and may lead to unneeded testing.  Refer to the Interference With Laboratory Tests section for more information on potential interferences.

Indications for Testing

Laboratory monitoring for monoclonal antibody therapeutics is appropriate in individuals receiving monoclonal antibody drugs (eg, adalimumab, infliximab). Laboratory monitoring can be used to optimize dosage or investigate treatment failure:

  • Primary treatment failure occurs when a patient does not initially respond to therapy. , , 
  • Secondary treatment failure occurs when there is a loss of previous response. , ,  This failure is often due to the presence of antidrug antibodies. , 

Refer to the Monitoring Strategies section for more detailed information about test timing.

Laboratory Testing

Monoclonal antibody therapeutic drug monitoring primarily involves two types of laboratory testing: drug concentration measurement and antidrug antibody detection.

Drug Concentration Testing

Drug concentration testing is used to assess the exact concentration of a biologic drug in a patient’s serum. Test methods include binding assays such as enzyme-linked immunosorbent assays (ELISAs) and high-mobility shift assays; functional assays such as cell-based reporter genes assays; and liquid chromatography-tandem mass spectrometry (LC-MS/MS). ,  This testing is used to determine whether the drug concentration falls within a specified therapeutic range: a lower concentration might render the drug ineffective, whereas exceeding the range might not offer added therapeutic benefits and may increase the risk of side effects.

Antidrug Antibody Testing

Monoclonal antibodies are (to a varying degree) immunogenic (ie, repeated use of a given monoclonal antibody drug may lead to the development of antidrug antibodies by the patient’s immune system). ,  These antibodies may interfere with drug function by neutralizing the drug or increasing its clearance, potentially resulting in treatment failure. ,  These antibodies may also trigger adverse reactions to the drug.  However, not all antidrug antibodies have direct clinical implications; antidrug antibody test results should be interpreted in the complete clinical context.

Standard methods for antidrug antibody detection include ELISAs, high-mobility shift assays, and cell-based reporter gene assays. ,  LC-MS/MS is not used to assess for antidrug antibodies. 

Monitoring Strategies

Two strategies are commonly used to monitor monoclonal antibody therapeutics:

  • Reactive monitoring is used to assess drug and/or antidrug antibody levels in response to a clinical event or symptom, typically a lack or loss of response (primary or secondary treatment failure), exacerbation of disease, or the development of adverse reactions. , 
  • Proactive monitoring is used to assess drug and/or antidrug antibody levels with the goal of optimizing the dosage for an individual patient. 

Reactive Monitoring

The standard strategy for reactive monitoring typically involves measurement of trough serum drug concentrations simultaneously with antidrug antibodies. ,  Results from these tests, in the context of the complete clinical scenario, can inform the management strategy. This approach has been systematically evaluated in the context of anti-TNF treatment for inflammatory bowel disease. , , , , 

Clinical Interpretation of Monoclonal Antibody Drug and Antidrug Antibody Testing Results in the Context of Loss of Responsea
Monoclonal Antibody DrugAntidrug AntibodyInterpretation
Not detectedNot detected

Likely subtherapeutic dose (nonimmune-mediated failure)

Consider higher dosage of drug or shortened dosing interval

Not detectedDetectedb

Possible immunogenicity (immune-mediated failure)

Consider another drug or drug class

Detected (below target)cNot detected

Likely subtherapeutic dose (nonimmune-mediated failure)

Consider higher dosage of drug or shortened dosing interval

Detected (above target)cNot detected

Likely pharmacodynamic (mechanistic) issues

Consider complete clinical scenario and other potential causes of treatment failure

Consider another drug class


Likely immunogenicity (immune-mediated failure)

Repeat testing (consider an alternative test method) to confirm positive results

Consider another drug or drug class

aLoss of response should not be defined by clinical symptoms alone. Ongoing inflammation should be objectively confirmed by laboratory testing for inflammatory markers (eg, C-reactive protein), imaging, and/or endoscopy. 

bLow concentrations of antidrug antibodies may be transient and diminish over time.  In many cases, including in anti-TNF drug testing, a consensus on the definitive cutoffs to differentiate between low and high concentrations of antidrug antibodies has not yet been reached. , 

cAppropriate target monoclonal antibody drug concentrations vary by drug, and cutoffs may differ between assays; results should be interpreted based on the specific assay used. 

Source: Lázár-Molnár, 2016 ; Lázár-Molnár, 2019 ; Cheifetz, 2021 ; Vande Casteele, 2013 

Proactive Drug Monitoring

Proactive drug monitoring entails regular laboratory testing for drug and/or antidrug antibody concentrations, regardless of the patient's clinical status, to individually optimize dosage.  Cheifetz et al  propose the following regarding the role of proactive drug monitoring for anti-TNF monoclonal antibody therapeutics (eg, adalimumab, infliximab):

  • Proactive drug monitoring of anti-TNF drugs should be performed after induction, at least one time during maintenance, and after reactive drug monitoring.
  • Proactive drug monitoring is most consequential for patients with high drug clearance or severely active disease.
  • Proactive drug monitoring to optimize anti-TNF monotherapy leads to better outcomes than unoptimized therapy.
  • Proactive drug monitoring to optimize anti-TNF monotherapy may be a useful alternative to combination anti-TNF therapy in some situations.
  • The same assay should be used for longitudinal proactive drug monitoring unless different assays have been fully standardized and cross-validated.

More studies are needed to support the use of proactive drug monitoring for other monoclonal antibody treatments. 

Interference With Laboratory Tests

Monoclonal antibody therapeutics have the potential to interfere with laboratory testing, including blood bank testing, monoclonal protein testing, and solid organ transplantation testing.  These interferences can have adverse effects on clinical care and may lead to unneeded additional testing.  The specific nature of the interference depends on the monoclonal antibody therapeutic, as do the techniques for addressing interference.  Consultation with the laboratory is advisable if interference is suspected. Careful communication is also advised to ensure that the laboratory is aware of the presence or possible presence of monoclonal antibody therapeutics. 

Examples of Monoclonal Antibody Therapeutic Interference With Laboratory Tests
Laboratory TestExamples of Monoclonal Antibody Therapeutics That May Cause InterferencePotential InterferencesTechniques Used to Address Interference
Blood bank testingDaratumumab


  • Agglutination tests
  • Direct antiglobulin tests
  • Panel reactive antibody screens

Plasma pretreatment with antiidiotype antibody

Plasma pretreatment with CD38

Treatment of RBCs with dithiothreitol

Monoclonal protein testing (serum protein electrophoresis and serum immunofixation by electrophoresis) for multiple myeloma




False-positive results for M protein

Daratumumab-specific immunofixation reflex assay

Electrophoresis protocols that distinguish between M protein and monoclonal antibody therapeutics

Mass spectrometry-based methods (if available)

Lymphocyte cross-match testing for solid organ transplantation





False-positive cross-match

Donor lymphocyte treatment with pronase

Serum pretreatment with antiidiotype antibodies

RBC, red blood cell

Source: Lázár-Molnár, 2019 

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Medical Experts



Julio Delgado, MD, MS
Executive Vice President, ARUP Laboratories
Professor, Vice Chairman, and Chief, Division of Clinical Pathology, University of Utah Department of Pathology