At the Basket Show in Farmington, ME I was fortunate to have had the opportunity to watch how they NPIP test birds. First there is a light box with a grid of glass (I think) over the light, then they put a purpleish solution on the glass, you turn your hen upside down and the man picks the vein under then hens wing. Drop of blood goes on the grid with a drop of solution, stirs it around and times it. If it comes out clear, you are NPIP negative (good thing) if it comes out 'grainy", then you take your bird directly out of the area with where other birds are. (of course dust can alter this test so don't go off the deep end quickly if it does come out positive) This old timer that was doing the tests says in all the years that he has given this test, he only had to send blood to the State of Maine for further testing a few times and only one had been positive. Here is a link http://www.clemson.edu/LPH/npip.htm and of course you can learn more about it by searching NPIP on the world wide web.