Objective To ascertain how anti-tumour necrosis factor (TNF) drug and anti-drug antibody levels testing is used in a ‘real-world’ setting to optimise inflammatory bowel disease (IBD) treatment.

Design Retrospective cohort study of prospectively collected patient data.

Setting Tertiary IBD centre in London, UK.

Patients All patients at Guy's and St Thomas' Hospitals on anti-TNF who had levels measured between the start of testing in 2012 and October 2014.

Interventions Anti-TNF drug and anti-drug antibody levels as part of routine monitoring.

Main outcome measures Indication for measuring levels and changes in management made as a result of the levels.

Results 330 infliximab levels were carried out in 199 patients and 143 adalimumab levels were carried out in 103 patients. Levels were primarily done in those with evidence of loss of response; 37% of infliximab levels and 52% of adalimumab levels. Levels resulted in a change in management in 26% of patients in infliximab group and 25% of patients in adalimumab group; however, this was greater in those with loss of response, 62% and 61% respectively. Anti-drug antibodies were detected in 7% of patients.

Conclusions Our early experience has demonstrated that measuring anti-TNF drug and anti-drug antibody levels can be useful in the optimisation of IBD management. In an increasing number of patients, particularly those with evidence of loss of response, it allows early decisions to be made regarding changing therapy. It also offers the potential for significant cost-saving by preventing pointless dose escalation in the context of therapeutic levels or when high-level anti-drug antibodies are present.