Most people think fasting means nothing to eat or drink after going to bed the night before a blood draw. Most patients make the mistake of avoiding anything by mouth, including water and medications. Fasting technically means nothing to eat or drink EXCEPT water and medications for 8-12 hours prior to a blood draw.
The reason for fasting is because of 2 tests – blood glucose (sugar) and the cholesterol panel. The only foods that will affect this are sugar or fat. Black coffee, plain tea, or other non-caloric beverages will not affect the results. Hydration with water actually helps make the veins more pronounced , maybe for an easier blood draw. Medications should NEVER be skipped for a fasting blood draw.