Answer
They are antibodies that neutralise factor VIII and can make replacement treatment less effective. They are detected using clinical assessment and blood tests.
Sources for this answer
- Esperoct 500 IU powder and solvent for solution for injection — Current selected SmPCemc · Summary of Product Characteristics
- NHSNHS · NHS medicine guidance
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.