Use the nicotine level that makes you comfortable, mindful of the fact a low level may make you creep back to the analogs. Concerning blood tests, I would think a full panel blood test would detect nic from vaping. Mine do, though the doctor never brings it up. LOL, once when I was smoking analogs, a doctor sat down to review my blood test with me. He was shocked when he came to the nic reading and thought maybe there was a mistake. I told him to calm down because I was a smoker. He had just listened to my chest and told me it sounded very good! Now, the first thing any health provider asks when you walk in the door is if you smoke. Now that I vape, I simply answer no, saving me the obligatory lecture and offer of expensive smoking cessation classes.