For blood work that requires fasting, it is typically necessary to fast for 8 to 12 hours before the test. During this fasting period, you should not eat or drink anything except plain water. It is also recommended to avoid chewing gum, smoking, exercising, and taking certain medications unless instructed otherwise by your doctor. Scheduling the blood test in the morning is advised so that most of the fasting period occurs while you are asleep. However, the exact fasting duration may vary depending on the specific blood test your doctor has ordered, so it is important to follow your healthcare provider's instructions closely.