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Test Code FIAIA Infliximab Quantitation with Reflex to Antibodies to Infliximab, Serum

Reporting Name

Infliximab QN with Reflex to Ab, S

Useful For

Trough level quantitation for evaluation of patients undergoing therapy with infliximab, infliximab-dyyb, infliximab-abda or infliximab-axxq

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Serum Red

Specimen Required

Patient Preparation:

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

2. 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.

Container/Tube: Red top (serum gel/SST are not acceptable)

Specimen Volume: 1 mL

Collection Instructions: Centrifuge within 2 hours of collection.

Specimen Minimum Volume

0.5 mL

Testing Algorithm

Infliximab will be performed by liquid chromatography-tandem mass spectrometry on all specimens. When infliximab results are below 5.1 mcg/mL, testing for antibodies to infliximab will be performed at an additional charge.

Specimen Stability Information

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

Reference Values


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


Pediatric reference ranges are not established.



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

Day(s) Performed

INFX: Monday, Wednesday, Thursday

INXAB: Monday, Wednesday, Friday

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


82397-(if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
INFXR Infliximab QN with Reflex to Ab, S 39803-2


Result ID Test Result Name Result LOINC Value
63000 Infliximab, S 39803-2
36847 Interpretation 59462-2

Clinical Reference

1. Colombel JF, Sandborn WJ, Reinisch W, et al: Infliximab, azathioprine, or combination therapy for Crohn's disease. N Engl J Med. 2010 Apr;362(15):1383-1395. doi: 10.1056/NEJMoa0904492

2. Jurgens M, Mahachie John JM, Cleynen I, et al: Levels of C-reactive protein are associated with response to infliximab therapy in patients with Crohn's disease. Clin Gastroenterol Hepatol. 2011 May;9(5):421-427.e1. doi: 10.1016/j.cgh.2011.02.008

3. Ordas I, Mould DR, Feagan BG, Sandborn WJ: Anti-TNF monoclonal antibodies in inflammatory bowel disease: pharmacokinetics-based dosing paradigms. Clin Pharmacol Ther. 2012 Apr;91(4):635-646. doi: 10.1038/clpt.2011.328

4. Afif W, Loftus EV Jr, Faubion WA, et al: Clinical utility of measuring infliximab and human anti-chimeric antibody concentrations in patients with inflammatory bowel disease. Am J Gastroenterol. 2010 May;105(5):1133-1139. doi: 10.1038/ajg.2010.9

5. Imaeda H, Bamba S, Takahashi K, et al: Relationship between serum infliximab trough levels and endoscopic activities in patients with Crohn's disease under scheduled maintenance treatment. J Gastroenterol. 2014 Apr;49(4):674-682. doi: 10.1007/s00535-013-0829-7

6. Steenholdt C, Bendtzen K, Brynskov J, et al: Cut-off levels and diagnostic accuracy of infliximab trough levels and anti-infliximab antibodies in Crohn's disease. Scand J Gastroenterol. 2011 Mar;46(3):310-318. doi: 10.3109/00365521.2010.536254

7. Feuerstein JD, Nguyen GC, Kupfer SS, et al: American Gastroenterological Association Institute guideline on therapeutic drug monitoring in inflammatory bowel disease. Gastroenterology. 2017 Sep;153(3):827-834. doi: 10.1053/j.gastro.2017.07.032

8. Silva-Ferreira F, Afonso J, Pinto-Lopes P, Magro F: A systematic review on infliximab and adalimumab drug monitoring: Levels, clinical outcomes and assays. Inflamm Bowel Dis. 2016 Sep;22(9):2289-2301. doi: 10.1097/MIB.0000000000000855

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 Sep;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 May;2(6):893-903. doi: 10.1373/jalm.2017.024869)

Report Available

3 to 6 days

Reject Due To

Gross hemolysis Reject
Gross lipemia OK
Gross icterus Reject

Method Name

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

INXAB: Electrochemiluminescent Bridging Immunoassay with Acid Dissociation


If not ordering electronically, complete, print, and send 1 of the following with specimen:

-Gastroenterology and Hepatology Client Test Request (T728)

-Therapeutics Test Request (T831)

Profile Information

Test ID Reporting Name Available Separately Always Performed
INFX Infliximab, S No Yes

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
INXAB Infliximab Ab, S No No