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Test Code INFXP Infliximab Quantitation with Antibodies to Infliximab, Serum


Specimen Required


Patient Preparation:

1. Draw blood immediately before next scheduled dose (trough specimen).

For 12 hours before specimen collection do not take multivitamins or dietary supplements containing biotin (vitamin B7), which is commonly found in hair, skin, and nail supplements and multivitamins.

Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 1.2 mL

Collection Instructions: Centrifuge and aliquot serum into plastic vial within 2 hours of collection.


Secondary ID

620151

Useful For

Trough level quantitation for evaluation of patients undergoing therapy with infliximab for proactive or reactive therapeutic drug monitoring.

Profile Information

Test ID Reporting Name Available Separately Always Performed
INFX Infliximab, S Yes, (INFXR) Yes
INXAB Infliximab Ab, S No Yes

Testing Algorithm

When this test is ordered, Infliximab quantitation and testing for antibodies to Infliximab will always be performed.

 

For more information see Ulcerative Colitis and Crohn Disease Therapeutic Drug Monitoring Algorithm.

Method Name

INFX: Selective Reaction Monitoring Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

INXAB: Electrochemiluminescent Bridging Immunoassay with Acid Dissociation

Specimen Type

Serum Red

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Red Refrigerated (preferred) 28 days
  Frozen  28 days

Reject Due To

Gross hemolysis Reject
Gross lipemia OK
Gross icterus Reject
Heat-Treated Reject

Reference Values

INFLIXIMAB QUANTITATION:

Limit of quantitation is 1.0 mcg/mL. Therapeutic ranges are disease specific.

 

Pediatric reference ranges are not established.

 

INFLIXIMAB ANTIBODIES

Absence of antibodies to infliximab (ATI) is defined as <50 U/mL

Presence of ATI is reported as positive when concentrations are ≥50 U/mL

Interpretation

Results above 35 mcg/mL are suggestive of a blood draw at a time-point in treatment other than trough.

 

Interpretation and patient management will be different according to disease state, clinical presentation (symptomatic versus appropriate response to therapy), several other laboratory tests and a combination of the drug concentration and presence of antibodies to infliximab.

 

IFX quant, mcg/mL

ATI, U/mL

Comment

<5

Negative

Absence of detectable antibody-to-infliximab (ATI). Low concentration of infliximab (IFX) may be attributable to other parameters related to infliximab clearance.

<5

Positive

Presence of ATI detected, which correlates with low concentration of infliximab. ATIs may be associated with increased clearance and lower circulating concentrations of IFX.

5-10

Negative

Absence of detectable ATI.

 

At this concentration of IFX, a low-titer ATI (50-499 U/mL) cannot be completely excluded. However, the presence of a high-titer ATI (≥500 U/mL) is unlikely.

 

If there is clinical suspicion for a low-titer ATI, suggest submission of a new sample obtained at trough.

 

This test has demonstrated drug tolerance of up to 100 mcg/mL IFX for ATI ≥500 U/mL and up to 10 mcg/mL IFX for ATI <500 U/mL

 

Low positive

(50-499 U/mL)

Presence of ATI detected. At this concentration of IFX, the detected titer of the ATI may be modestly underestimated.

 

This test has demonstrated drug tolerance of up to 100 mcg/mL IFX for ATI ≥500 U/mL and up to 10 mcg/mL IFX for ATI <500 U/mL

 

High positive

(≥500 U/mL)

Presence of ATI detected.

 

This test has demonstrated drug tolerance of up to 100 mcg/mL IFX for ATI ≥500 U/mL and up to 10 mcg/mL IFX for ATI <500 U/mL

>10

Negative

Absence of detectable ATI.

 

At this concentration of IFX, a low-titer ATI (50-499 U/mL) cannot be completely excluded. The presence of a high-titer ATI (≥500 U/mL) is unlikely, but also cannot be completely excluded.

 

If there is clinical suspicion for an ATI, suggest submission of a new sample at trough, preferably during maintenance phase. This test has demonstrated drug tolerance of up to 100 mcg/mL IFX for ATI ≥500 U/mL and up to 10 mcg/mL IFX for ATI <500 U/mL

 

Low positive

(50-499 U/mL)

Presence of ATI detected. At this concentration of IFX, the detected titer of the ATI may be underestimated.

 

Suggest submission of a new sample obtained at trough, preferably during maintenance phase.

 

This test has demonstrated drug tolerance of up to 100 mcg/mL IFX for ATI ≥500 U/mL and up to 10 mcg/mL IFX for ATI <500 U/mL

 

High positive

(≥500 U/mL)

Presence of ATI detected. This test has demonstrated drug tolerance of up to 100 mcg/mL IFX for ATI ≥500 U/mL and up to 10 mcg/mL IFX for ATI <500 U/mL

Method Description

Infliximab Quantitation:

This test is performed using liquid-chromatography and tandem mass spectrometry. Preanalytical sample preparation includes a trypsin digestion; unique clonotypic peptides from the light chain of the infliximab chimeric structure (IgG1 kappa) are monitored.(Willrich MAV, Murray DL, Barnidge DR, et al. Quantitation of infliximab using clonotypic peptides and selective reaction monitoring by LC-MS/MS. Int Immunopharmacol. 2015;28(1):513-520. doi: 10.1016/j.intimp.2015.07.007)

 

Infliximab Antibodies:

This lab developed immunoassay is designed to measure antibodies-to-infliximab (ATI) in human serum by means of electrochemiluminescence (ECL) on the MesoScale Discovery (MSD) platform. The assay uses a "bridging" format in which the ATI forms a link between biotin labeled infliximab and SULFO-Tag labeled infliximab. The biotin binds to a streptavidin (SA) coated surface and the SULFO-Tag creates a signal in the presence of a conjugate following application of an electric current via the MSD QuickPlex SA120. During sample preparation, serum is mixed with acetic acid to break the infliximab/ATI complex. Biotinylated and SULFO-Tagged infliximab are then added together with buffer containing Tris-HCL pH 10 to neutralize the pH and bind with ATI that is present in the sample. After the incubation with the labeled drug, the calibrators, controls, and samples are added to a SA plate that has been blocked with a solution of bovine serum albumin. The biotinylated infliximab then binds to the SA plate. After an incubation period, the SA plate is washed, and MSD read buffer is added. Immediately after the addition of read buffer, the plate is analyzed on the MSD QuickPlex SQ120. The read buffer provides an appropriate chemical environment for ECL when a voltage is applied to the electrodes on the plate by the MSD QuickPlex SQ120. This voltage causes bound SULFO-Tagged infliximab to emit measurable light. The MSD QuickPlex SQ120 measures the intensity of emitted light and correlates it to a set of standards with known concentrations of ATI by means of a 4-point logistics curve fitting method.(Willrich MAV, Lazar-Molnar E, Snyder MR, Delgado JC. Comparison of clinical laboratory assays for measuring serum infliximab and antibodies to infliximab. J Appl Lab Med. 2018;2(6):893-903. doi:10.1373/jalm.2017.024869)

Day(s) Performed

INFX: Monday, Wednesday, Thursday

INXAB: Monday, Wednesday, Friday

Report Available

3 to 6 days

Specimen Retention Time

2 weeks

Performing Laboratory

Mayo Clinic Laboratories in Rochester

CPT Code Information

INFX - 80230

INXAB - 82397

LOINC Code Information

Test ID Test Order Name Order LOINC Value
INFXP Infliximab QN with Antibodies, S 103791-0

 

Result ID Test Result Name Result LOINC Value
63417 Infliximab Ab, S 72623-2
63000 Infliximab, S 39803-2
36847 Interpretation 59462-2
36654 INXAB Interpretation 59462-2

Forms

If not ordering electronically, complete, print, and send a Gastroenterology and Hepatology Test Request (T728) with the specimen.