Comparison of α2AP antigen with activity levels. Levels of total free α2AP antigen, C-terminally intact α2AP antigen, and percentage of C-terminally cleaved α2AP were compared with activity α2AP levels as measured using a chromogenic substrate assay in a subset of 60 plasma samples from the MEGA study.^23,24  There was no clear relationship between total α2AP antigen levels and α2AP activity levels, whereas C-terminally intact α2AP levels and percentage of C-terminally cleaved α2AP showed a positive and negative association, respectively.