Background:
Accurate measurement of factor VIII (FVIII) activity in patients with hemophilia A is important for patient monitoring and treatment decisions. Discrepancies in results using different assays or reagents to measure prolonged–half-life factor products have been recognized. BAY 94-9027 is a prolonged–half-life FVIII product site-specifically conjugated with a 60-kDa polyethylene glycol molecule (2×30 kDa branched).
Objective:
A global field study was conducted to assess the ability of clinical laboratories to measure BAY 94-9027 activity in spiked hemophilic plasma samples using their in-house or specific assays.
Design/Method:
In this 2-part study, laboratories received sample sets (3–4 per laboratory) of 26 blinded samples in randomized order for analysis. Each set consisted of triplicate test samples of BAY 94-9027 or a comparator (antihemophilic factor [recombinant] plasma/albumin-free method [rAHF-PFM (Advate® ); Shire]) spiked at low (<10 IU/dL), medium (10–50 IU/dL), and high (50–100 IU/dL) concentrations in pooled hemophilic plasma. Normal control plasma and unspiked hemophilic plasma in triplicate were positive and negative controls, respectively. Two additional blinded samples matching 2 of the other 24 samples in the set were included in each set to decrease the predictability of each set. Laboratories analyzed test samples using their in-house assays (one-stage, chromogenic, or both), reagents, and standards (part 1). In part 2, all laboratories tested 2 additional sample sets using 2 activated partial thromboplastin time kits (Pathromtin® and HemosIL® SynthASil) previously shown to accurately measure BAY 94-9027 and full-length FVIII. FVIII recovery and FVIII levels were primary and secondary endpoints, respectively.
Results:
Fifty-two laboratories in North America, Europe, and Israel participated in the study. In part 1, 49 laboratories tested samples using the one-stage assay, 16 used the chromogenic assay, and 13 used both assays. The reagents routinely used for measuring FVIII activity varied among participating laboratories. Mean FVIII recovery ranged from 75.1%‒103.2% for BAY 94-9027 and 94.6%‒114.7% for rAHF-PFM across all concentrations and reagents using the one-stage assay. As expected based on previously published data, the PTT-A and HemosIL® APTT-SP kits underestimated BAY 94-9027 at all concentrations. More accurate one-stage results were generated using the Pathromtin® and SynthASil kits, as shown in part 2 of the study. For the chromogenic assay, mean FVIII recovery ranged from 104.4%‒117.1% for BAY 94-9027 and 87.7%‒107.8% for rAHF-PFM across all concentrations.
Conclusion:
BAY 94-9027 can be accurately monitored using the chromogenic assay and select commonly used one-stage assay kits without need of a conversion factor.