was trinken vor blutabnahme — what can you do yourself?

Before a blood draw, the most important self-action is to drink plain water – but only still water. Caffeinated drinks like coffee, black or green tea, and cola can affect lab values (e.g., glucose, cortisol, liver enzymes). Fruit juices, milk, or smoothies break the fasting state and distort blood lipids or sugar. Alcohol should be avoided for at least 24 hours prior, as it alters liver enzymes and triglycerides. This advice is critical for fasting blood tests (glucose, lipid panel). If you are not required to fast, water is still fine, but avoid caloric or caffeinated beverages. Drinking too much water (over 1 liter shortly before) can dilute electrolytes and skew sodium or potassium levels. One glass (200–300 ml) is ideal. The evidence is based on clinical practice and laboratory medicine guidelines, not on a single trial. Caveat: For specialized tests (e.g., cortisol day profile, oral glucose tolerance test), different instructions apply – always follow your doctor’s orders. Self-prescribed 'detox' or 'diuretic' teas before the draw are not recommended and may distort results.