Pilotdown Man
You are right, there will always be some amount of alcohol in your blood. But in India they use breathalyser. A few years ago doctors used Alco Tester III, and it was possible to fool the machine by sucking the air rather than blowing in to it. Now almost all of them use Alco Tester IV, it is not possible to suck the air as there is a diaphragm in the tube that allows only one way flow of air (now it is also possible to remove the diaphragm and use it and that is why doctors give you brand new tube every time so it is not tempered with).
Every time I was tested in India my results were always 0.00 I never saw reading higher than that, of course if they had tested my blood it probably wouldn't have been all zeros.