This corrigendum corrects the article by Bowyer et al1 The error was published on page e206, where the article reads:

In the presence of emicizumab, FVIII inhibitor titres should, therefore, be measured by a chromogenic Bethesda assay using reagents that are either exclusively bovine or contain bovine FIXa and human FX.

It should read:

In the presence of emicizumab, FVIII inhibitor titres should, therefore, be measured by a chromogenic Bethesda assay using reagents that are either exclusively bovine or contain Bovine FX and human FIXa.