There are devices called "tenderfoots" that cut a measured slice in the heel. Warming the foot in a warm cloth or bowl of warm water helps, too. The test is usually 3-4 paper circles that need to be filled in with blood, so the person doing the test sometimes needs to "milk" the foot to get enough blood to ensure the lab has enough to do the tests. The milking shouldn't be that uncomfortable.
There have been accounts of the heel being cut too deeply, needing stitches or causing nerve damage, but that has declined considerably since most hospitals stopped using scapels and started using lancets.
Each state mandates differents tests. While the test is often called the PKU test, it usually has more things tested, as pamamidwife
mentioned. There's been some lobbying to include more tests, as the cost goes down when everyone does them.
I will soon be talking to someone who works in the state office. I will definitely ask about what our state does with the tests and about whether a test could be returned to the mother afterwards. My curiosity has been aroused on this question!
I started a new thread to talk about privacy issues with blood testing. Maybe you could come help me learn? http://www.mothering.com/discussions...67#post2416967