With certain blood tests, you may be instructed to fast for up to eight hours before your appointment. Fasting before a blood draw means you don't eat or drink. Apr 26, "I drank black coffee before a cholesterol test. Will it affect the results?". Jul 17, Caffeine addicts must pay special attention to their doctors' orders for blood tests needed for routine health checks and diagnostics. Depending. Top 4 Drinks That Make Intermittent Fasting EASIER - Drink This, Not That!