Measurement of recombinant porcine factor VIII in patients with congenital haemophilia A and inhibitors in the presence of emicizumab

Abstract Introduction Recombinant porcine factor VIII (rpFVIII) is a treatment option for break‐through bleeds in patients with congenital haemophilia A with inhibitors (CHAwI) on emicizumab. However, there are limited data about the measurement of rpFVIII in the presence of emicizumab. Aim To analyse whether rpFVIII can be measured with a chromogenic assay with bovine component (bCSA) in plasma from CHAwI on emicizumab treatment. Methods In the first part of the study, FVIII deficient plasma was spiked with rpFVIII, in the second part, commercial plasma from CHAwI was spiked with emicizumab and rpFVIII, and in the third part, plasma from CHAwI on emicizumab treatment was spiked with rpFVIII. FVIII was then measured with bCSA and a chromogenic assay with human component (hCSA). Thrombin generation (TG) and clot‐waveform analysis (CWA) were also carried out. Results The recovery of rpFVIII measured with bCSA is approximately 80% and is further influenced by the presence of an anti‐porcine inhibitor. rpFVIII assessed with hCSA was influenced by emicizumab. CWA and TG showed a weak correlation with baseline emicizumab concentration, but peak thrombin and CWA correlated well with increasing emicizumab concentrations and rpFVIII activities. Conclusion This study indicates that rpFVIII can be measured in the presence of emicizumab with a bCSA. A calibration curve for the measurement of rpFVIII with bCSA should be established.