For what reason serum cu and ceruloplasmin levels are paradoxically low in wilson's disease?

Not paradoxical: The problem is that copper can't get out of certain cells. The reason for ceruloplasmin being low is under study; since it carries copper, this metal also tends to be low. Checking serum copper and serum ceruloplasmin as a screen for wilson's misses up to a quarter of cases, especially if the person is already sick with anything.