It depends on what is being tested. Pricking your finger is generally just to check a blood-glucose level, which is used to determine whether or not your body is manufacturing the proper hormones to manage the sugars you eat.
If you're being tested for any other number of things, including STD/STIs, then they're more than likely going to draw blood from your arm in addition to the physical observation of your genital area and clutures they take from there.
Tim, as in "Donate"
"Each has his past shut in him like the leaves of a book known only to him by his heart, and his friends can only read the title." -- Virginia Woolf.
[This message has been edited by Dude_who_writes (edited 09-01-2004).]