was essen vor blutabnahme — which blood markers matter?

What to eat before a blood draw depends on which markers are being measured. For many routine tests (complete blood count, liver/kidney function, thyroid hormones), fasting is not required. However, certain markers demand an 8–12 hour fast, most notably fasting glucose and the lipid panel (total cholesterol, LDL, HDL, triglycerides). A fatty meal can dramatically elevate triglycerides and skew LDL calculations. The oral glucose tolerance test (OGTT) also requires strict fasting. Recent guidelines (e.g., from the American Heart Association) have relaxed fasting requirements for lipid panels in non-high-risk individuals, but many labs still recommend 8–12 hours. Water is generally allowed and even encouraged to prevent dehydration. Coffee, tea, or juice can interfere (caffeine, sugar). For hormone tests (cortisol, estradiol, progesterone), timing and cycle phase matter more than food intake. Consumer tests like MyBody-X's Fertility Check provide specific instructions. Bottom line: always check lab instructions; when in doubt, fast but drink water. Evidence is based on clinical practice and guidelines, not a single study.