Fasting before bloodwork sounds simple in theory, don’t eat, show up, get your blood drawn. But in practice, the rules are more specific than most people realize, and small mistakes can throw off results enough to require a repeat visit. Can you drink water? What about coffee? Do medications count as breaking a fast? These blood test preparation tips exist for a reason: certain lab values, like glucose and triglycerides, are directly affected by recent food intake, and inaccurate results can lead to unnecessary follow-up testing or a misreading of your actual health status. This guide breaks down exactly what fasting before bloodwork requires, what’s actually allowed, and the most common mistakes that quietly compromise results.