^ARG531^HIS,^ALA284^GLU, and^SER289^LEU proteins exhibit unstable activity during the first phase of the 2-st chromogenic assay.

Conditioned medium from COS cells expressing FVIII WT or mutant protein was collected 64 hours after transfection and analyzed in a modified 2-stage activity assay (COAMATIC). The first stage of the assay was modified such that each protein was subjected to increasing duration of the first stage. FVIII, ■; ^ARG531^HIS, ○;^SER289^LEU, ▵;^ALA284^GLU, ⋄.