No it won't appear on your blood work. They have to be testing you for that certain drug in order for them to know your doing it.
Drugs of any sort affect the balance of other chemicals in the body as your body reacts to the drug (when you take prescription meds, these changes are sometimes listed as side effects). As for whether weed will make anything abnormal enough to cause doctors to notice, I suppose it depends on what they are testing for. I know that my own endocrinologist routinely checks for kidney function, a1c level, thyroid, cholesterol levels, and sometimes a multitude of other things when routine lab work is done. As for whether weed will show up if they are not looking for it, I suppose it really depends on what they are looking for at the time, and how normal your levels are. Nobody on this forum can say for sure since we don't see the paperwork. If I were you, I would truly be more concerned about whether weed will alter any of the other items so that the lab test is not a true indication of your health. That would be the big issue... you want to KNOW if anything is starting to go wrong and you need all of those numbers to be accurate. You might want to consider this as you plan timing for lab tests.