If they drug test all newborns, what does the epidural show up as?

I asked a question earlier, asking if they drug test all newborns, and I got about 90% "yes" answers. Anyway, if they do, then what does the epidural and narcotics (my "what to expect when your expecting" book says they may give you a shot of narcotics, like demarol, before the epidural) show up as? Or do they just test for street drugs (like Cocaine, pot, ect). But even heroin shows up as morphine in a drug test. What does the epidural show up as? an opiod??