Wow. When I saw your subject line,
I thought you were asking about how to keep the child from freaking out
during the actual blood draw procedure.
But you have already had the blood drawn.
So . . . your concerns are about why they wanted the sample
and what they are looking for,
if the pediatrician has not explained this to your satisfaction,
is there a nurse advisor associated with his or her office?
Sometimes a nurse advisor can take more time
and explain things in more detail than the pediatrician can.
Meanwhile, however, the pediatrician may have some things
he/she is checking for and didn't want to worry you
before finding out some of the measurements/values in the sample.
After they check the values, they may have some results/suggestions
to discuss with you.
Try not to worry.
If they have anything to discuss with you,
they'll also have suggestions about what's the best thing to do.
If you can, perhaps bring a friend (a sister? a cousin?)
with you to take notes, in case it's hard for you
to focus on what they may tell you.