Approximation of emicizumab plasma levels in emergency situations. A practical approach.

INTRODUCTION A dedicated emicizumab assay based on the modified one-stage factor VIII (FVIII) assay (mOSA) is mainly available in haemophilia treatment centres (HTC). A method to estimate emicizumab plasma levels based on a widely available assay would be desirable, especially for emergency situations. AIM A method for emicizumab plasma level approximation (ELA) using a routine FVIII activity measurement with standard one-stage assay (sOSA) was developed and evaluated. METHOD Within this pilot study, 59 samples from patients with severe haemophilia A with (n = 8) and without (n = 8) inhibitors under emicizumab treatment were analysed using sOSA following a manual 1:8 sample pre-test dilution with saline. The sOSA was determined in two different laboratories, using two different analyser platforms each. RESULTS The results demonstrated an excellent correlation of approximated emicizumab plasma levels (ELA) with the emicizumab plasma concentration determined with mOSA (r > .9; p < .05). The ELA showed a sensitivity of 93.3% and a specificity of 89.6% to predict a pre-defined cut-off-value of ≤30 µg/ml for the discrimination between subtherapeutic and therapeutic emicizumab plasma levels. CONCLUSION Approximation of emicizumab levels by standard one-stage FVIII assay discriminates between subtherapeutic and therapeutic emicizumab levels and might facilitate clinical decision-making in emergency situations, such as bleeding, trauma or urgent surgery in case that dedicated emicizumab assays are not available.