Blood testing is not only the most invasive form of drug testing, it's also the most accurate. If you're a stoner scheduled to give blood for a drug test, you're pretty much screwed - at least in the short term. Happily, drugs disappear from the blood stream in a very short time. Stay away from toxins for twenty-four to forty-eight hours and your blood should be clean as a whistle. Also remember that the blood test is the most expensive, which means blood tests are the least common method of scrutiny. Legal herbs that clean the blood are easily detected in a blood test, so there are not a lot of options other than to wait it out (and, really, if you can't chill out for twenty-four hours you've got a bigger problem than a drug test). But it's all academic. Unless there's a lot of money or a lot of law at stake, the odds say you'll never be compelled to give blood.