Effects of emicizumab on APTT, one-stage and chromogenic assays of factor VIII in artificially spiked plasma and in samples from haemophilia A patients with inhibitors.

The APTT was significantly shortened in the presence of emicizumab. sOSA FVIII:C levels were erroneously high, and it is not recommended that these be performed. Quantification of emicizumab concentration was possible by mOSA. Human CSA was sensitive to emicizumab and surrogate FVIII:C activity could be determined. Bovine CSA were insensitive to emicizumab and could not be used to quantify emicizumab concentration.