PB0170 - Evaluation of the Extended-Half Life FVIII products' measurement accuracy and precision with five different types of laboratory assays.

Background: The Extended half-life products (EHL), with modified pharmacokinetic profile, were recently introduced in the clinical practice for person with haemophilia A (PwH). The structural differences, compared to standard half-life products, generate reagent-dependent discrepancies in the measurement of their level when the calibration curve is constructed with equivalent plasma wild-type molecules, as shown by previous studies when one-stage clotting assay (OSA) and chromogenic assay (CSA) were used in FVIII activity measurements on EHL-FVIII products.

Aims: The accuracy and precision of measurements, by five different laboratory assays, were tested for Damoctocog alpha-pegol, Rurioctocog alpha-pegol, Turoctocog alpha-pegol, and Efmoroctocog alpha.

Methods: EHL-FVIIIs were reconstituted according to the manufacturer's instructions and serial dilutions (1.0-0.025 IU/mL and 0.1-0.006125 IU/mL concentration ranges) were obtained by using HemosIL® FVIII Deficient Plasma (Werfen). FVIII:C was tested with three OSAs: aPTT-based reagents with colloidal silica (Synthasil®, Werfen-IL); ellagic acid (Synthafax®, Werfen-IL); OSA-calibrated with each EHL-rFVIII product and colloidal silica. Measurements were also carried out with two different commercially available CSAs (Coamatic® Factor VIII®, Chromogenix-Werfen) and Trinichrom FVIII® (Tcoag-Stago). Bland-Altman analysis was performed to compare all assays at high and low EHL-rFVIII concentrations.

Results: The classical OSA and CSA showed significant discrepancies between the expected and measured EHL-rFVIII concentrations, while the calibrated-OSA was accurate and precise in determining the activity of all EHL-rFVIIIs in the in-vitro settings. Comparable results were found using ex-vivo plasma samples (from PwH A under prophylaxis with EHL-products). Bland Altman analysis showed a significant disagreement in FVIII measured levels by comparing each method with the specific EHL-rFVIII calibrated-OSA, taken as the most accurate method. Moreover, a proportional bias (positive or negative) was observed in most cases both at higher and lower concentration range.

Conclusion(s): A calibration curve constructed with each EHL-rFVIII product could avoid inaccurate laboratory results, which might negatively impact the efficacy and safety of patient management.