The Correction Factor for Monitoring Efanesoctocog Alfa Is Not Always 2.5
Sean Platton, Jude Platton, Katarzyna Kniola, Laura Aiken, Janine Collins, Suthesh Sivapalaratnam, Priyanka RahejaABSTRACT
Introduction
Efanesoctocog alfa (Altuvoct) is a recombinant super‐extended half‐life factor (F)VIII concentrate licensed in the United Kingdom for patients with severe and moderate haemophilia A. Concentrate potency is assigned by one‐stage assays (OSA) using Actin FSL. Chromogenic FVIII:C assays (CA) and some OSA are inaccurate for Altuvoct; the product information sheet suggests results of these be divided by 2.5 to approximate FVIII:C. UK experts recommend against using correction factors (CF), with guidance that only validated OSA should be used for Altuvoct, or, in the presence of FVIII‐mimetics, that CA results are reported with a caveat about assay inaccuracy.
Methods
Over four months, we assessed the impact of a fixed CF on FVIII:C, testing 70 samples collected during pharmacokinetic assessment when patients switched to Altuvoct. All were tested using OSA (Actin FSL and Actin FS) and CA (BIOPHEN and Siemens FVIII:C) on a Sysmex CN‐6500 analyser, calibrated against a plasma standard.
Results
For samples with Altuvoct between 10 and 269 IU/dL, CF increased as FVIII:C increased when using CA and decreased when using OSA (Actin FS), suggesting that a single CF across that range is inappropriate.
Conclusions
A universal CF for Altuvoct assays may lead to clinically significant FVIII:C underestimation across the measurement range, and is inappropriate in most cases. Should product‐specific calibrators (and controls) become available, laboratories should verify their assays for Altuvoct using them so that CF are not required.