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Infliximab Level and Antibodies


Infliximab Level and Antibodies
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Reference Range:

Level - None
A detectable anti-TNF trough level (immediately pre-dose) is associated with a higher rate of clinical and endoscopic remission

Antibodies - Positive = >10 AU/mL

Turnaround Time:

14 Working Days


Internal Test Code:- IFXL


Indication: IBD patients treated with Infliximab (anti-TNF)

Background: Patients may respond well to treatment initially, only to encounter loss or response further ahead in their treatment pathway. Others may not respond to treatment at all. Outcomes may be improved for patients on Infliximab by measuring trough drug levels and to determine if patients have developed antibodies to the drug.
There is further data to come from the Personalised Anti-TNF Therapy in Crohn's disease (PANTS) study. However, there is a consensus to test both drug and antibody in the settings listed below:
Week 14 testing for all patients, including confirmation of primary non-response.
Following loss of response. At a 12 month review to guide treatment decisions such as drug withdrawal, dose or interval change

Method: Enzyme Linked Immunosorbent Assay (ELISA)

Repeat Frequency: As Clinically Indicated



Vessels and Containers:

Serum gold-top

Sample Requirements:

500ul serum


Biotin Interference

Biotin is widely available as an over the counter (OTC) supplement and is commonly included in multivitamins as well as supplements marketed for hair and nails. Biotin is occasionally prescribed in pregnancy and renal failure, as well as being used at high doses in the treatment of multiple sclerosis, mitochondrial energy disorders and various inborn errors of metabolism. In patients taking supra-physiological doses of biotin, serum biotin levels may be as high as 1160ug/L one hour after taking a single oral dose of 300mg biotin. Biotin has been shown to significantly interfere with certain assays resulting in incorrect test results which may go undetected. Biotin in patient samples can cause falsely low results which could lead to inappropriate patient management or misdiagnosis. In order to investigate interference from Biotin several samples were spiked with up to 1200 ng/ml biotin and analysed.

Results for Infliximab antibodies showed the possibility of lowered results when biotin concentration is >100 ng/ml

We suggest that you ask patients whether they are taking biotin and bear it in mind when interpreting their test results. The advice from the manufacturer for patients taking biotin is that samples should be collected just before a dose (i.e. at trough level).

How result is reported:

Negative or numeric in AU/L

Important Information:

Entry Last Modified 21/01/2020

Transportation and Handling:

At room temperature

Special Precautions:


Time limits for requesting additional examinations:

Sample available in this laboratory for approximately 2 weeks. Test can only be added to samples already received by the immunology laboratory and within this time period.