Gary Churak's Answer
The Blood test will probably read that you have THC in your system. Marijuana, which the basic formula for the drug is THC, stays in your system about 30 days. So, the chances are that it would show up in your system. Now, the question is if you smoke three days ago, why were they pulling you over for DWI at that time? There may be an issue as to probable cause for the arrest down the road the fact that you had such a small amount in your system at the time that you were driving.