was trinken vor blutabnahme — what are common causes?

The question of what to drink before a blood draw is medically well-established: plain, unsweetened water is generally allowed and even encouraged to prevent dehydration, which can make veins harder to access. Coffee, tea, fruit juices, soft drinks, or milk can interfere with many lab values – especially fasting glucose, triglycerides, electrolytes, and liver enzymes. Even 'sugar-free' drinks with artificial sweeteners or flavors may affect insulin secretion or metabolism. Common causes of skewed results include: 1) caloric or sugary beverages breaking the fast; 2) caffeine raising cortisol and heart rate; 3) alcohol altering liver markers and blood lipids. The evidence is based on decades of laboratory medicine and clinical practice, not on single randomized trials. For specific tests (e.g., oral glucose tolerance test), strict protocols apply. Patients should always follow their physician's or lab's instructions. Safety note: during prolonged fasting (≥12 h), water can help prevent dizziness or fainting.