Optimal monitoring of bypass therapy in hemophilia A patients with inhibitors by the use of clot waveform analysis

Abstract

Background: Assays to determine the optimal hemostatic effects of bypass therapy in hemophilia A (HA) patients with inhibitors are difficult to compare. Clot waveform analysis (CWA), based on the continuous monitoring of routine coagulation parameters (prothrombin time/activated partial thromboplastin time), offers a useful method for assessing global clotting function.

Objectives: To investigate the technique of CWA for the hemostatic monitoring of bypass therapy in HA patients with inhibitors.

Methods and results: Ellagic acid (Elg), tissue factor (TF) or both (Elg/TF) were used as trigger reagents in CWA. The standard parameters - clot time (CT), maximum coagulation velocity (|min1|), and acceleration (|min2|) - were recorded. Optimal monitoring was defined as: (i) a significant difference in these parameters between plasma from HA patients with inhibitors and normal plasmas; and (ii) a significant improvement in these indices in HA patients with inhibitors after bypass therapy. Experiments in vitro demonstrated that there were significant differences between plasma from HA patients with inhibitors and normal plasma with various triggers, in the order Elg > Elg/TF >> TF. Addition of therapeutically achievable concentrations of bypassing agents, however, showed significant improvements in the different parameters only with Elg/TF, suggesting that this reagent provided the most appropriate assay. A total of 20 plasmas from HA patients with inhibitors in which bypassing agents were infused were evaluated ex vivo by Elg/TF CWA. The postinfusion parameters CT and |min2| reflected clinical effects, and were close to normal levels. Furthermore, Elg/TF CWA facilitated quantitative evaluation of perioperative hemostatic management of bypass therapy in HA patients with inhibitors.

Conclusions: CWA is a promising method for the quantitative monitoring of bypass therapy during routine automated clotting assays with a modified trigger reagent comprising a well-balanced mixture of Elg and TF.

Keywords: blood coagulation factor inhibitors; clinical laboratory techniques; factor VIII; hemophilia A; hemostatic techniques.