Performance of Factor VIII Extended Half‐Life Product Measurements in External Quality Assessment Programmes

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Abstract
Introduction: Improvements in treatment of patients with haemophilia A have meant that their quality of life has majorly improved. However, a disadvantage to these developments has come at a cost to the laboratory when monitoring patient Factor VIII (FVIII) levels and there is the potential for under‐ or overtreatment leading to clinical risk towards the patient. Methods: A global study performed in 2023 to investigate the differences in FVIII assay results in a large cohort of laboratories has enabled users to understand the challenges that new products can cause. Five FVIII modified/extended half‐life (EHL) products were studied by distributing spiked samples via 3 external quality assessment (EQA) schemes (ECAT, NEQAS and RCPAQAP). Results: Participating laboratories used either one‐stage assays (OSA), chromogenic assays (CA), or both methods when performing the assays. Most centres running the OSA used IL Hemosil Synthasil, Siemens Actin FS, Siemens Pathromtin SL, or Stago Cephalin/Kaolin/C.K. Prest reagents, and for the CA, the Chromogenix Coamatic FVIII kit and the Siemens chromogenic FVIII kit were utilised. Conclusion: The FVIII results submitted by participants showed that currently available OSA and CA do not provide consistent results in some products with both an under‐ and over‐estimation of the expected recovery based on potency at either concentration level. Results for Afstyla Lonoctocog alfa suggest that centres were not clear on whether OSA results were before or after application of the correction factor (multiplication of initial result by 2).

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