Global Hemostatic Methods to Tailor Treatment With Bypassing Agents in Hemophilia A With Inhibitors- A Single-Center, Pilot Study

For patients with hemophilia A and high-titer inhibitors treated with bypassing agents there are no reliable methods to assess treatment effect. We investigated the utility of global hemostatic methods in assessing treatment with bypassing agents (rFVIIa or activated prothrombin complex [aPCC]). All patients with hemophilia A and inhibitors followed at the Coagulation Unit or the Pediatric Coagulation Unit at Karolinska University Hospital aged 6 years and above were eligible for this noninterventional study. Baseline plasma samples were spiked with bypassing agents in increasing concentrations (aPCC 50 U/kg, 100 U/kg, 150 U/kg, and rFVIIa 90 μg/kg and 270 μg/kg) in vitro. For patients treated with factor concentrates or bypassing agents follow-up samples were collected (in vivo tests). The samples were analyzed using overall hemostatic potential (OHP), and calibrated automated thrombogram, Calibrated Automated Thrombogram (CAT). Nine patients with hemophilia A with inhibitors were included. Spiking with rFVIIa normalized the coagulation potential in 6/8 samples, in 3 only with high dose. Only one sample did not improve adequately after spiking with aPCC. The improvement in hemostasis was reliably shown by both CAT and OHP. The baseline potential was, however, more often measurable by OHP compared to CAT. Factor concentrate had been administered to 5 patients normalizing the hemostatic potential in vivo in 2 (without spiking). The hemostatic improvement induced by spiking with rFVIIa or aPCC is shown by OHP and CAT, but the results have to be evaluated in larger cohorts.