I can't wait to try this ...
Artfully Dodging Blood-Test Fears (Contemporary Pediatrics)
Between 5 and 12 years of age, children often ask, at the beginning of their annual physical exam, whether they need a blood test. I've learned to dodge this question because, if you tell a child that a blood count is in her immediate future, she asks over and over when it's going to happen and whether it will hurt. My dodge is simply to tell the child that I won't know if she needs a blood test until the end of the visit.
Once the moment of truth arrives, I use a simple technique to distract the child. After I tell her that she will need a finger poke, I quickly add that the reason for the test is to find out if she is an alien. I then take out a test tube filled with green or purple "blood" and mention that someone from outer space came in for a physical the previous week. This usually gets the child's mind off the poke and onto whether I'm making up the alien thing and what's really in the test tube (food coloring and water—an off-label use). The technique doesn't always work, but we have a lot of fun when it does.