PB0073 - FIX Post infusion monitoring surveys: Results and analysis from the updated UK NEQAS BC Haemophilia programmes 2024

Background: Laboratory results for FIX assays have become more complex to understand due to the introduction of new therapeutic FIX drug products for the treatment of patients with haemophilia B. The UK NEQAS BC haemophilia EQA programmes for FIX post infusion treatment have been updated to reflect this change in FIX treatment and help laboratories to understand these challenges

Aims: In this survey we wanted to highlight the use of non-recommended methods/reagents on FIX laboratory results.

Methods: In this UK NEQAS BC FIX post infusion monitoring survey 59 centres participated. FIX deficient plasma from a severe haemophilia B donor ( < 1IU/dL FIX) was spiked with 4 different FIX drug products: Alprolix, Benefix, Idelvion and Refixia at different concentration levels. Participating centres were asked to use recommended (by manufacturer/published data) methods/reagents for laboratory monitoring.

Results: Data was returned from 47 centres. Centres performed either one stage assays (OSA), chromogenic assays (CA) or both.

OSA
Alprolix Median value, 40 IU/dL with CV = 8.7%; Benefix Median value, 14.3 IU/dL with CV = 13.6%; Idelvion Median value, 20.4 IU/dL with CV = 14.5% and Refixia Median value, 15.4 IU/dL with CV = 18.2%

CA
Alprolix Median value, 35.7 IU/dL; Benefix Median value, 11.7 IU/dL; Idelvion Median value, 24.8 IU/dL and Refixia Median value, 13.4 IU/dL.

The expected potency recoveries for the neqas samples differed from the overall median results as 6% of participants testing Alprolix and 38% of participants testing Refixia used a non-recommended reagent.

Conclusion(s): The UK NEQAS BC FIX post infusion monitoring surveys are a valuable tool to highlight the methods and reagents that should be used when monitoring FIX drug products post infusion. The survey results can show over- and under-estimation of FIX results when using a non-recommended method/reagent due to the different sensitivities of the reagent compositions in either the OSA or CA kits.