Ordering Recommendation

Use to evaluate response failure to infliximab or biosimilar therapy. Use to determine and adjust dosage or identify the need for change to another anti-TNF-α inhibitor.
If infliximab drug level is not detected, infliximab neutralizing antibody will be added. To assess for both infliximab activity and neutralizing antibody titer regardless of infliximab drug level, see Infliximab or Biosimilar Activity and Neutralizing Antibody (2008320).

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Collect specimens before next infliximab or biosimilar treatment.


Serum Separator Tube (SST).

Specimen Preparation

Separate from cells ASAP or within 2 hours of collection. Transfer 1 mL serum to an ARUP Standard Transport Tube. (Min: 0.5 mL)

Storage/Transport Temperature


Unacceptable Conditions

Contaminated, hemolyzed, icteric, or lipemic specimens.


After separation from cells: Ambient: 48 hours; Refrigerated: 4 weeks; Frozen: 1 year (avoid repeated freeze/thaw cycles)


Cell Culture/Quantitative Chemiluminescent Immunoassay (CLIA)




2-3 days

Reference Interval

Components Reference Interval
Infliximab Activity w/Rflx to Ab Not Detected
Infliximab Neutralizing Antibody Titer Not Detected

Interpretive Data

This test measures the capacity of infliximab to neutralize TNF activity. If infliximab is not detected, testing for neutralizing antibodies (NAb) will be performed. Infliximab NAb titer is obtained by identifying the minimal serum dilution at which blocking of infliximab activity is no longer observed.

This test is used to evaluate secondary response failures to infliximab therapy. Secondary response failure is defined as loss of clinical response after initial improvement of clinical signs and symptoms. Therapeutic decision should rest on both the clinical response and the knowledge of the fate of the drug including the emergence of immunogenicity in individual patients.

Circulating infliximab levels have been shown to vary considerably between patients. These differences relate to route and frequency of administration and patient-related features such as age, gender, weight, drug metabolism, and concomitant medications such as methotrexate and other immunosuppressants.

*AGA recommended target trough concentration for reactive monitoring of patients with active IBD on maintenance therapy is 5 ug/mL or greater for infliximab (Feuerstein JD, et al. Gastroenterology. 2017;153:827-834). The AGA makes no recommendation regarding the use of routine, proactive therapeutic drug monitoring in adults with quiescent IBD treated with anti-TNF agents.

This test was developed and its performance characteristics determined by ARUP Laboratories. It has not been cleared or approved by the US Food and Drug Administration. This test was performed in a CLIA-certified laboratory and is intended for clinical purposes.

Clinical Interpretation of Infliximab and Antibody Testing Results in the Context of Treatment Failure
Infliximab Activity
Infliximab Neutralizing Antibody Titer
Not Detected Not Detected Sub-therapeutic dose. A higher dosage of infliximab or shortening the dosing interval may be appropriate.
Not Detected Detected Likely immune-mediated treatment failure. A change to another anti-TNF drug may be appropriate.
Detected - Below Target* N/A Sub-therapeutic dose. A higher dosage of infliximab or shortening the dosing interval may be appropriate.
Detected - Above Target* N/A A change to another type of therapy (not targeting TNF) may be appropriate, if the patient is not responding adequately to infliximab therapy.

Compliance Category

Laboratory Developed Test (LDT)


This test is performed pursuant to an agreement with Svar Life Sciences. If Infliximab drug level is not detected, then Infliximab Neutralizing Antibody Titer will be added. Additional charges apply.

Hotline History


CPT Codes

80230; if reflexed, add 82397


Component Test Code* Component Chart Name LOINC
2013613 Infliximab Activity w/Rflx to Ab 39803-2
2013614 EER Infliximab Activity w/Rflx to Ab 11502-2
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • Anti-TNF-alpha Drug
  • Avsola
  • Human Anti-Chimeric Antibody
  • IFD
  • Inflectra
  • Infliximab-abda
  • Infliximab-dyyb
  • Infliximab/HACA measurement
  • Ixifi
  • Remicade
  • Renflexis
  • TNFa antibody
Infliximab or Biosimilar Activity with Reflex to Antibody