Validation of factor VIII activity for monitoring standard and extended half-life products and correlation to thrombin generation assays.

Introduction: Monitoring replacement therapy with standard and extended half-life (EHL) products is challenging, since one-stage assay (OSA) and chromogenic substrate assay (CSA) results may differ significantly. Recent recommendations include local validation of each new product with recovery within 20-30%, depending on activity level.

Aim: To validate factor VIII (FVIII) activity for monitoring products in clinical use on Atellica Coag and to correlate it with thrombin generation.

Methods: Plasma samples spiked with Advate , Elocta , Adynovi , Nuwiq , NovoEight and Afstyla (0.05, 0.20, 0.50 and 0.80 IU/ml) were analysed using Atellica Coag 360 with CSA-1 (Coatest SP) and CSA-2 (FVIII chromogenic), and OSA (Actin FS). Thrombin generation was performed using two thrombin generation assays (TGA-1 (Thrombinoscope) and TGA-2 (Technothrombin).

Results: All products at levels above 0.05 IU/ml, except Adynovi, showed acceptable recovery using CSA-1, whereas measurements using CSA-2 gave more results outside the target level. All products, except Afstyla, showed acceptable recovery using OSA. Correlation between CSA-1 and OSA was excellent (r =1.0) with biases of 6-3​2%, depending on FVIII product. A clear dose-response was seen for all thrombin generation parameters and products using both methods, except at low levels for lag time using TGA-1. With CSA-1 as an independent variable, the correlations to thrombin peak (measured with TGA-2) were good (r  = .8-.9).

Conclusion: Our data revealed good correlation and acceptable bias between CSA and OSA using our sets of reagents, methods and analyser in spiked samples. Thrombin generation gave good correlation to CSA-1 factor activity and is a possible complement to factor activity assays.