Complement levels can be increased with inflammation, rising before other markers such as the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP).
I actually just took this off the internet. It really didn't say much else or I would have given you the link. I read this in a couple of places. It sounds like if your Lupus is active it can cause cause the high complement levels.
I hope it helps a little anyway.