Assay

Infliximab

Key Words

Infliximab Serology , IFXS

Specimen Collection

Serum (Brown)

Turnaround time

28 days

This test is referred to another centre:

Department of Clinical Biochemistry

City Hospital

Dudley road

Birmingham

B18 7QH

0121 507 3441

Test indications

Infliximab (Remicade®) is a chimeric human-mouse monoclonal antibody directed against tumour necrosis factor alpha (TNF), approved for use in the treatment of various chronic inflammatory diseases including rheumatoid arthritis, severe crohn’s disease and ankylosing spondylitis. The drug is administered as an infusion with a dosing interval ranging from 2-16 weeks.

Infusion of a standard dose of infliximab leads to highly variable inter-individual serum drug concentrations partly due to the development of anti-infliximab antibodies, which bind to infliximab leading to loss of therapeutic effect. Serum trough drug levels have been shown to correlate with clinical response and duration of effect.

A trough serum infliximab concentration of <1 µg/mL, in a patient on maintenance infliximab, indicates sub-therapeutic levels. If anti-infliximab, antibodies are present, further drug dose increases/infusion interval decreases are less likely to be effective and a change in drug therapy should be considered. In patients with low levels of infliximab but absent antibodies, a dose increase/infusion interval decrease may improve response and here it may be useful to remeasure the serum infliximab levels prior to the next infusion.

Antibodies will only be tested if indicated by a trough serum concentration of <1.0 µg/mL

Methodology

ELISA

Interferences

Contact referral

Reference Range

Cut off for a therapeutic trough infliximab level - >1.0 µg/mL

Antibodies

Negative: <10 AU/mL

Borderline positive: 10-20 AU/mL

Positive: >20 AU/mL

Analytical error

Contact referral lab

Reference change value

Contact referral lab