Tissue Factor/Factor XIa dual activated thrombin generation is able to reliably measure thrombin generation at all hemophilia A disease severities

Introduction: Predicting bleeding in hemophilia A is difficult due to limitations of existing factor VIII (FVIII) activity assays, which correlate poorly with clinical bleeding tendency. Measurement of thrombin generation (TG) by calibrated automated thrombography (CAT) may be an alternative to predict bleeding as it measures an individual’s complete plasma derived coagulation potential, rather than just focussing on one part of the coagulation cascade. However lack of standardization limit its applicability. Objective: To evaluate the ability of our standardized tissue factor (TF)/factor XI (FXI)a dual-activated thrombin generation assay (TGA) to assess TG across severe, moderate, and mild hemophilia A. Secondarily we evaluate whether varying TG levels at similar FVIII concentrations translate to different clinical bleeding tendencies. Materials and Methods: Plasma samples from 657 adult patients with hemophilia A of all severities included in the Hemophilia in the Netherlands 6 (HiN6) study were used. Samples were collected through standardized protocols from six Dutch hemophilia treatment centres, and stored in a centralized biobank. FVIII activity was centrally measured using one-stage assays. Thrombin generation was measured using our in-house TF/FXIa TG assay protocol using 1 pM TF, 100 pM FXIa, and 30 µM phospholipids. Bleeding tendencies were analysed based on patient questionnaires. Results: The TF/FXIa dual-activated TGA protocol was able to measure thrombin generation across all severities of hemophilia A. Median peak heights (PH) were 119.5 nM, 98.9 nM and 214.7 nM for severe, moderate and mild respectively. Moreover, the assay showed substantial variation in interindividual TG levels among patients with comparable FVIII activity levels (coefficient of variance of 99%, 83% and 47% for severe, moderate and mild HA respectively). However, TG did not differentiate between patients with and without self-reported bleeding in this study. Conclusion: The standardized TF/FXIa dual-activated TGA represents a tool for assessing individual coagulation potential in hemophilia A. More research is needed to further characterise the interindividual differences in thrombin generations at similar FVIII levels and possibly linking these results to bleeding tendency.