Can I drink black coffee before blood work that requires a 12 hour fast?

No. Fasting requires no food and no beverages (water may be allowable). Coffee contains caffeine ; other chemicals that can enter your blood stream. Drinking black coffee can skew some laboratory tests. It is not a true 12 hour fast if you drink coffee.
Fasting. Yes. Of course. Every primary care specialist will advise you to avoid calories when you are fasting. So water and black coffee are the two things that are allowed. Every office I have worked at tells their patients this when they are told to fast prior to coming in for these lab tests.