wie viel wasser vor blutabnahme — what are common causes?

Before a blood draw, it is generally recommended to drink 1–2 glasses (200–500 ml) of plain water, unless instructed otherwise by your doctor. Water helps make veins more visible, facilitates the puncture, and prevents dizziness or fainting. For fasting blood tests (e.g., glucose, lipids), water is allowed because it does not affect metabolic parameters. Common causes for this advice include: dehydration after overnight fasting, difficult vein access in elderly or athletic individuals, and prevention of vasovagal reactions. However, avoid coffee, tea, juice, or milk – they can interfere with results. For certain tests (e.g., sodium, osmolality), excessive water intake may alter values, so always follow specific lab instructions. The evidence is based on clinical practice guidelines, not high-quality trials.